Q.1 What is the primary physical principle that allows optical coherence tomography (OCT) to generate cross‑sectional images of tissue?
Diffraction of light in a scattering medium
Fourier transform of time‑delayed interference patterns
Absorption of UV photons by chromophores
Thermal expansion of tissue due to laser heating
Explanation - OCT uses low‑coherence interferometry. Light reflected from different depths interferes; the resulting interference pattern is Fourier‑transformed to reconstruct depth‑resolved reflectivity.
Correct answer is: Fourier transform of time‑delayed interference patterns
Q.2 Which wavelength region is most commonly used for near‑infrared spectroscopy (NIRS) in brain imaging?
UV (200–400 nm)
Visible (400–700 nm)
Near‑IR (700–1300 nm)
Mid‑IR (3–5 µm)
Explanation - Near‑IR wavelengths penetrate biological tissues relatively well and are minimally absorbed by water and hemoglobin, making them ideal for NIRS.
Correct answer is: Near‑IR (700–1300 nm)
Q.3 Which of the following detectors is most suitable for detecting single photons in optical imaging?
Photodiode
Photomultiplier tube (PMT)
Charge‑coupled device (CCD)
CMOS sensor
Explanation - PMTs amplify the signal from a single incident photon via dynodes, achieving high sensitivity and low noise for low‑light imaging.
Correct answer is: Photomultiplier tube (PMT)
Q.4 What does the term 'contrast agent' refer to in optical imaging?
A material that increases the refractive index of the imaging system
A substance that enhances the absorption or fluorescence signal in tissue
A filter that selects specific wavelengths
A software algorithm that improves image resolution
Explanation - Contrast agents bind to specific biomarkers, increasing the optical signal (absorption, scattering, or fluorescence) to improve image contrast.
Correct answer is: A substance that enhances the absorption or fluorescence signal in tissue
Q.5 Which optical phenomenon limits the lateral resolution of a confocal microscope?
Chromatic aberration
Diffraction limit
Light scattering
Photobleaching
Explanation - The smallest focusable spot is limited by diffraction, typically ~λ/(2NA), determining the lateral resolution.
Correct answer is: Diffraction limit
Q.6 In photoacoustic imaging, what is the primary source of acoustic signals?
Thermal expansion caused by absorbed optical energy
Mechanical vibrations of the tissue
Electrical currents in the imaging probe
Magnetic field interactions
Explanation - Absorbed light heats the tissue, causing rapid thermal expansion and generating ultrasonic waves that are detected.
Correct answer is: Thermal expansion caused by absorbed optical energy
Q.7 Which of the following best describes the Beer‑Lambert law?
The intensity of reflected light is proportional to the square of the distance
Light intensity decreases exponentially with the product of absorption coefficient and path length
The refractive index of a material is proportional to its density
The energy of a photon is inversely proportional to its wavelength
Explanation - Beer‑Lambert law models how light is absorbed as it travels through a medium.
Correct answer is: Light intensity decreases exponentially with the product of absorption coefficient and path length
Q.8 What safety class is a laser emitting 10 mW at 650 nm in the visible range?
Class 1
Class 2
Class 3R
Class 4
Explanation - Class 2 lasers are safe for accidental viewing up to ~0.5 s; 10 mW at 650 nm falls within this category.
Correct answer is: Class 2
Q.9 Which optical fiber type is best suited for long‑range medical imaging probes?
Multimode fiber with 50 µm core
Single‑mode fiber with 9 µm core
Photonic crystal fiber with hollow core
Plastic optical fiber with 250 µm core
Explanation - Single‑mode fibers minimize modal dispersion, preserving the coherence needed for imaging over long distances.
Correct answer is: Single‑mode fiber with 9 µm core
Q.10 What is the main advantage of using a pulsed laser over a continuous‑wave laser in optical tomography?
Higher average power
Reduced heating of tissue
Increased temporal resolution for depth discrimination
Simpler system design
Explanation - Pulsed lasers provide short bursts that enable time‑of‑flight measurements to separate signals from different depths.
Correct answer is: Increased temporal resolution for depth discrimination
Q.11 Which imaging technique uses the principle of Brillouin scattering to assess tissue elasticity?
Optical coherence elastography
Raman spectroscopy
Brillouin microscopy
Multiphoton microscopy
Explanation - Brillouin microscopy measures frequency shifts due to acoustic phonons, providing information on viscoelastic properties.
Correct answer is: Brillouin microscopy
Q.12 In fluorescence imaging, what is 'photobleaching'?
Increase in fluorescence intensity over time
Permanent loss of fluorescence due to prolonged excitation
Conversion of fluorescence to heat
Amplification of signal by a photomultiplier
Explanation - Photobleaching occurs when fluorophores irreversibly lose their ability to emit light after repeated excitation.
Correct answer is: Permanent loss of fluorescence due to prolonged excitation
Q.13 Which parameter defines the depth of penetration for light in biological tissue?
Numerical aperture
Mie scattering coefficient
Reduced scattering coefficient
Refractive index mismatch
Explanation - The reduced scattering coefficient (µ_s') determines how far light can travel before being significantly scattered.
Correct answer is: Reduced scattering coefficient
Q.14 Which of the following best describes the term 'optical density' in tissue imaging?
The density of optical fibers used in the system
The measure of light absorption per unit length
The refractive index of the imaging medium
The number of photons detected per pixel
Explanation - Optical density quantifies how much light is attenuated per unit distance, related to absorption coefficient.
Correct answer is: The measure of light absorption per unit length
Q.15 Which component in an OCT system is responsible for generating the reference arm path?
Beam splitter
Photodiode array
Electro‑optic modulator
Laser cavity
Explanation - The beam splitter splits the source beam into sample and reference paths, enabling interferometry.
Correct answer is: Beam splitter
Q.16 Which wavelength range is typically used for thermal imaging in medical diagnostics?
400–700 nm
700–1100 nm
3–5 µm
10–12 µm
Explanation - Long‑wave infrared (10–12 µm) corresponds to the thermal radiation peak of human tissues (~37 °C).
Correct answer is: 10–12 µm
Q.17 What does 'spectral unmixing' aim to achieve in hyperspectral medical imaging?
Combine multiple spectral bands into a single image
Separate overlapping spectral signatures of different chromophores
Convert spectral data into RGB format
Remove noise from the spectral signal
Explanation - Spectral unmixing decomposes measured spectra into contributions from known components, improving tissue characterization.
Correct answer is: Separate overlapping spectral signatures of different chromophores
Q.18 Which optical property is most directly affected by the concentration of hemoglobin in tissue?
Refractive index
Absorption coefficient
Scattering coefficient
Fluorescence lifetime
Explanation - Hemoglobin strongly absorbs light in the visible and near‑IR ranges, influencing the absorption coefficient.
Correct answer is: Absorption coefficient
Q.19 In a confocal microscope, how is out‑of‑focus light rejected?
By using a pinhole placed conjugate to the focal plane
By employing a high‑NA objective lens
By applying a low‑pass filter
By increasing the illumination intensity
Explanation - The pinhole blocks light from points not in focus, enhancing optical sectioning.
Correct answer is: By using a pinhole placed conjugate to the focal plane
Q.20 Which of the following is a key advantage of using a fiber bundle for endoscopic imaging?
Unlimited field of view
High mechanical stiffness
Flexibility and remote light delivery
Intrinsic optical filtering
Explanation - Fiber bundles allow flexible probes, delivering light to and collecting light from the tissue.
Correct answer is: Flexibility and remote light delivery
Q.21 What role does the 'numerical aperture' (NA) of an objective lens play in optical imaging?
Determines the maximum depth of field
Sets the maximum illumination power
Controls the amount of light collected and the resolution
Limits the speed of the scanning system
Explanation - Higher NA allows more light collection and improves lateral resolution due to smaller diffraction limit.
Correct answer is: Controls the amount of light collected and the resolution
Q.22 Which detector technology is best suited for high‑speed, large‑area imaging in optical tomography?
CMOS sensor
Photodiode array
Photomultiplier tube
Electron‑multiplying CCD (EMCCD)
Explanation - CMOS sensors provide rapid readout over large areas, essential for real‑time imaging.
Correct answer is: CMOS sensor
Q.23 In optical imaging, what is the primary source of background noise when using a laser source?
Shot noise from photon detection
Thermal noise in the detector electronics
Backscatter from optical components
Ambient light leakage
Explanation - Shot noise, inherent to photon counting statistics, dominates when using coherent laser illumination.
Correct answer is: Shot noise from photon detection
Q.24 What is the main purpose of a 'reference arm' in a Michelson interferometer used for OCT?
To modulate the laser frequency
To provide a time delay for depth scanning
To generate a known path length for interference
To stabilize the optical alignment
Explanation - The reference arm provides a controllable optical delay that matches sample path lengths for constructive interference.
Correct answer is: To generate a known path length for interference
Q.25 Which of the following is NOT a typical application of infrared imaging in medicine?
Monitoring skin temperature for inflammation
Visualizing bone fractures
Assessing blood oxygenation
Detecting tumor metabolism
Explanation - Infrared imaging lacks the penetration and resolution to detect fractures; modalities like X‑ray are used.
Correct answer is: Visualizing bone fractures
Q.26 Which optical phenomenon causes the speckle pattern seen in coherent imaging systems?
Diffraction
Scattering interference
Chromatic dispersion
Photobleaching
Explanation - Speckle arises from interference between coherent waves scattered from many microscopic features.
Correct answer is: Scattering interference
Q.27 What is the key advantage of using a laser diode over a solid‑state laser for portable medical imaging?
Higher output power
Compact size and low power consumption
Lower coherence length
Higher beam quality
Explanation - Laser diodes are small, efficient, and well suited for handheld imaging systems.
Correct answer is: Compact size and low power consumption
Q.28 In optical imaging, the term 'field of view' refers to:
The depth of focus
The area on the sensor that captures light
The number of pixels in the detector
The range of wavelengths used
Explanation - Field of view (FOV) is the spatial extent of the image captured by the system.
Correct answer is: The area on the sensor that captures light
Q.29 Which of the following best describes the 'diffraction limit' in optical imaging?
The maximum depth that can be imaged
The minimum resolvable distance between two points
The maximum number of photons that can be detected per second
The limit of laser power before tissue burns
Explanation - Diffraction limit defines the smallest detail that can be distinguished due to wave nature of light.
Correct answer is: The minimum resolvable distance between two points
Q.30 What is 'fluorescence lifetime imaging microscopy' (FLIM) used for?
Measuring tissue temperature
Determining the time a fluorophore remains excited before emitting a photon
Mapping blood flow speed
Counting the number of photons per pixel
Explanation - FLIM measures the decay time of fluorescence, which can reveal local biochemical environments.
Correct answer is: Determining the time a fluorophore remains excited before emitting a photon
Q.31 Which material is commonly used as a near‑infrared window for tissue imaging due to its low absorption?
Water
Oxygenated hemoglobin
Deoxygenated hemoglobin
Melanin
Explanation - Water has minimal absorption between ~700–1300 nm, forming the NIR window for deep tissue imaging.
Correct answer is: Water
Q.32 Which of these is a primary advantage of using a 'fiber‑optic probe' in surgical imaging?
High cost
Impossibility of remote sensing
High flexibility and minimal invasiveness
Limited spectral range
Explanation - Fiber‑optic probes can navigate through narrow pathways, reducing surgical trauma.
Correct answer is: High flexibility and minimal invasiveness
Q.33 What is the purpose of a 'lock‑in amplifier' in optical spectroscopy?
To increase laser power
To filter out noise by synchronizing with the excitation signal
To convert optical signals to electrical signals
To cool the detector
Explanation - Lock‑in amplifiers detect signals at a known reference frequency, enhancing signal‑to‑noise ratio.
Correct answer is: To filter out noise by synchronizing with the excitation signal
Q.34 Which of the following is NOT a type of optical contrast mechanism?
Absorption
Scattering
Refractive index modulation
Acoustic impedance mismatch
Explanation - Acoustic impedance mismatch is relevant to ultrasound, not optical contrast.
Correct answer is: Acoustic impedance mismatch
Q.35 In a spectral‑domain OCT system, what is the role of the Fourier transform?
Converts time‑domain signals to frequency domain
Computes the depth profile from spectral interference patterns
Measures the amplitude of the light source
Aligns the optical beam with the detector
Explanation - Spectral‑domain OCT records spectral interference and applies a Fourier transform to obtain axial reflectivity.
Correct answer is: Computes the depth profile from spectral interference patterns
Q.36 What is the primary safety concern when using high‑power lasers in a medical imaging setting?
Eye damage due to accidental exposure
Electrical shock from the laser driver
Thermal burns from the beam hitting tissue
All of the above
Explanation - Laser safety involves protecting eyes, preventing electrical hazards, and avoiding tissue heating.
Correct answer is: All of the above
Q.37 Which of the following is a key factor influencing the axial resolution in OCT?
Beam diameter
Numerical aperture
Central wavelength
Bandwidth of the light source
Explanation - A broader bandwidth shortens the coherence length, improving axial resolution.
Correct answer is: Bandwidth of the light source
Q.38 In photoacoustic imaging, why are longer wavelengths (e.g., 1064 nm) often preferred for deeper tissue penetration?
They have higher absorption by water
They are less scattered and absorbed by hemoglobin
They generate stronger acoustic signals
They are less expensive to generate
Explanation - Near‑IR wavelengths experience lower absorption and scattering, enabling deeper imaging.
Correct answer is: They are less scattered and absorbed by hemoglobin
Q.39 Which of these optical imaging modalities uses two-photon absorption for excitation?
Confocal microscopy
Multiphoton microscopy
Optical coherence tomography
Near‑IR spectroscopy
Explanation - Multiphoton microscopy excites fluorophores via simultaneous absorption of two photons, enabling deeper tissue imaging.
Correct answer is: Multiphoton microscopy
Q.40 In optical imaging, what does the term 'signal‑to‑noise ratio' (SNR) represent?
The ratio of pixel count to the total number of photons
The ratio of detected signal power to background noise power
The ratio of laser output power to detector sensitivity
The ratio of tissue thickness to light penetration depth
Explanation - SNR quantifies how clear the signal is relative to random noise.
Correct answer is: The ratio of detected signal power to background noise power
Q.41 Which component in a laser driver circuit is responsible for maintaining a stable current to the laser diode?
Voltage regulator
Current mirror
Oscillator
Heat sink
Explanation - A current mirror ensures constant current despite supply variations, stabilizing laser output.
Correct answer is: Current mirror
Q.42 What is the typical depth resolution of a conventional OCT system using a 1‑µm bandwidth light source?
5 µm
50 µm
500 µm
5 mm
Explanation - A 1‑µm bandwidth gives a coherence length of roughly 50 µm, setting axial resolution.
Correct answer is: 50 µm
Q.43 Which imaging modality is most suitable for visualizing blood vessels in the retina?
Optical coherence tomography angiography (OCTA)
Thermal imaging
Ultrasound imaging
MRI
Explanation - OCTA provides depth‑resolved vascular maps by detecting motion contrast in OCT data.
Correct answer is: Optical coherence tomography angiography (OCTA)
Q.44 What does 'photothermal effect' refer to in optical imaging?
Light absorption leading to local temperature rise
Emission of photons from heated tissue
Change in refractive index due to temperature
Conversion of thermal energy to electrical signals
Explanation - When tissue absorbs light, it heats up, producing photothermal signals used in imaging.
Correct answer is: Light absorption leading to local temperature rise
Q.45 Which of the following is an example of a 'structured illumination' technique?
Confocal microscopy
Multiphoton excitation
Optical coherence tomography
Diffuse reflectance spectroscopy
Explanation - Confocal uses a pinhole to block out‑of‑focus light, effectively structuring illumination.
Correct answer is: Confocal microscopy
Q.46 Which property of tissue determines how much light is scattered at a given wavelength?
Absorption coefficient
Reduced scattering coefficient
Molar mass
Refractive index
Explanation - The reduced scattering coefficient quantifies how quickly photons are redirected in tissue.
Correct answer is: Reduced scattering coefficient
Q.47 What is the main advantage of using a swept‑source OCT over a Fourier‑domain OCT?
Higher lateral resolution
Faster acquisition speed
Lower cost
Simpler optical alignment
Explanation - Swept‑source OCT scans the wavelength quickly, enabling rapid imaging of dynamic tissues.
Correct answer is: Faster acquisition speed
Q.48 Which type of detector is most suitable for low‑light, high‑resolution imaging in fluorescence microscopy?
Photodiode
EMCCD
Photomultiplier tube
CMOS
Explanation - Electron‑multiplying CCDs provide high sensitivity and low noise for faint fluorescence signals.
Correct answer is: EMCCD
Q.49 Which parameter determines the penetration depth of a laser beam in tissue?
Wavelength
Pulse duration
Beam diameter
Laser power
Explanation - Longer wavelengths penetrate deeper due to lower scattering and absorption.
Correct answer is: Wavelength
Q.50 Which of the following describes the 'NIR window' in medical imaging?
A spectral region where water absorption is maximum
A wavelength range (700–1300 nm) where light penetration in tissue is optimal
A bandwidth of 10 nm around 800 nm
A window in the spectrum blocked by atmospheric gases
Explanation - The NIR window offers low absorption by tissue chromophores, facilitating deeper imaging.
Correct answer is: A wavelength range (700–1300 nm) where light penetration in tissue is optimal
Q.51 What is the purpose of using a 'beam expander' before a microscope objective?
To increase the numerical aperture
To reduce the beam divergence
To match the beam diameter to the objective’s back aperture
To split the beam into multiple paths
Explanation - Expanding the beam ensures full utilization of the objective’s NA and improves resolution.
Correct answer is: To match the beam diameter to the objective’s back aperture
Q.52 Which type of optical imaging is most suitable for monitoring the thermal signature of a feverish patient?
Near‑IR fluorescence imaging
Thermal infrared imaging
Confocal microscopy
Optical coherence tomography
Explanation - Thermal IR cameras capture emitted radiation corresponding to body temperature.
Correct answer is: Thermal infrared imaging
Q.53 What is the primary reason for using a 'polarizing beam splitter' in a Michelson interferometer?
To reduce laser power
To separate orthogonal polarization components for reference and sample arms
To generate a high‑frequency modulation
To improve beam alignment
Explanation - Polarizing beam splitters direct differently polarized light into distinct paths.
Correct answer is: To separate orthogonal polarization components for reference and sample arms
Q.54 Which parameter is crucial for determining the sensitivity of an optical imaging system?
Numerical aperture
Detector quantum efficiency
Laser pulse repetition rate
Optical bandwidth
Explanation - High quantum efficiency ensures more photons are converted to measurable signals.
Correct answer is: Detector quantum efficiency
Q.55 What is the main difference between 'time‑domain OCT' and 'spectral‑domain OCT'?
Time‑domain uses a moving reference mirror, spectral‑domain uses a stationary reference
Spectral‑domain provides higher resolution
Time‑domain cannot image depth
Spectral‑domain requires a laser source
Explanation - TD‑OCT scans by mechanically moving the reference arm; SD‑OCT records spectra in a static setup.
Correct answer is: Time‑domain uses a moving reference mirror, spectral‑domain uses a stationary reference
Q.56 Which of the following is NOT a typical application of optical imaging in cancer diagnostics?
Detection of tumor margins during surgery
Monitoring tumor oxygenation
Assessing bone density
Identifying malignant lesions via fluorescence
Explanation - Bone density is better evaluated with X‑ray or DEXA; optical imaging excels in soft tissue imaging.
Correct answer is: Assessing bone density
Q.57 Which component of an optical imaging system is responsible for converting optical signals to electrical signals?
Beam splitter
Photodetector
Laser source
Optical fiber
Explanation - Photodetectors (photodiodes, CCDs, PMTs) convert photons to measurable electrical currents.
Correct answer is: Photodetector
Q.58 In an OCT system, why is it important to match the dispersion of the sample arm to that of the reference arm?
To improve lateral resolution
To maintain interference contrast and reduce axial blurring
To increase the field of view
To reduce laser power requirements
Explanation - Dispersion mismatches broaden the coherence function, degrading axial resolution.
Correct answer is: To maintain interference contrast and reduce axial blurring
Q.59 Which type of laser is commonly used for high‑resolution dermatological imaging?
CO₂ laser
Nd:YAG laser at 1064 nm
Diode laser at 532 nm
Er:YAG laser at 2940 nm
Explanation - Nd:YAG lasers provide deep penetration with moderate absorption, suitable for imaging skin layers.
Correct answer is: Nd:YAG laser at 1064 nm
Q.60 What is the role of a 'digital signal processor (DSP)' in an optical imaging system?
Generate the light source
Amplify the optical signal
Process raw data for image reconstruction and filtering
Stabilize the detector temperature
Explanation - DSPs perform real‑time algorithms, such as FFTs and noise reduction, for image creation.
Correct answer is: Process raw data for image reconstruction and filtering
Q.61 Which imaging modality uses a 'pump–probe' approach to measure tissue oxygenation?
Near‑IR spectroscopy
Optical coherence tomography
Multiphoton microscopy
Thermal imaging
Explanation - Pump–probe NIR spectroscopy monitors changes in hemoglobin absorption to assess oxygenation.
Correct answer is: Near‑IR spectroscopy
Q.62 What is the primary benefit of using a 'dual‑band' imaging system in medical diagnostics?
Increased depth resolution
Simultaneous acquisition of two spectral regions for better tissue contrast
Reduced laser power consumption
Higher frame rates
Explanation - Dual‑band imaging captures complementary information (e.g., visible + NIR) enhancing diagnostic value.
Correct answer is: Simultaneous acquisition of two spectral regions for better tissue contrast
Q.63 Which of the following is a typical noise source in fiber‑optic endoscopy?
Shot noise
Backscattering from fiber cladding
Ambient light leakage
All of the above
Explanation - All listed phenomena contribute to noise in fiber‑optic imaging systems.
Correct answer is: All of the above
Q.64 What does 'spectral resolution' refer to in optical imaging?
The ability to distinguish between different depths
The ability to resolve small spectral features or wavelengths
The pixel resolution in the image sensor
The speed at which images can be acquired
Explanation - Spectral resolution determines how finely the system can differentiate wavelengths.
Correct answer is: The ability to resolve small spectral features or wavelengths
Q.65 Which optical component is used to adjust the beam diameter before it enters a microscope objective?
Beam expander
Diffuser
Polarizer
Beam splitter
Explanation - A beam expander scales the beam to match the objective’s acceptance cone.
Correct answer is: Beam expander
Q.66 What is the main difference between 'thermal imaging' and 'infrared spectroscopy'?
Thermal imaging captures emitted radiation; spectroscopy measures absorption and emission at specific wavelengths
Thermal imaging is for living tissue; spectroscopy is for non‑living tissue
Spectroscopy uses lasers; thermal imaging uses LEDs
There is no difference
Explanation - Thermal imaging maps temperature, while spectroscopy analyzes material composition.
Correct answer is: Thermal imaging captures emitted radiation; spectroscopy measures absorption and emission at specific wavelengths
Q.67 Which property of light does 'coherence length' describe?
The range of wavelengths emitted
The distance over which the light wave maintains a predictable phase relationship
The intensity of the light source
The speed of light in the medium
Explanation - Coherence length limits the depth resolution in interferometric imaging.
Correct answer is: The distance over which the light wave maintains a predictable phase relationship
Q.68 Which of the following is an advantage of using a 'fiber‑coupled LED' as a light source?
High temporal coherence
Low power consumption and broad beam
High spatial coherence
High spectral purity
Explanation - LEDs are energy‑efficient and provide a wide, diffused illumination suitable for imaging.
Correct answer is: Low power consumption and broad beam
Q.69 In optical imaging, what is a 'point spread function' (PSF)?
The pattern of light spread from a point source after passing through the optical system
The time it takes to spread the light across the detector
The maximum intensity of the light source
The distribution of wavelengths emitted by the source
Explanation - PSF describes how a single point is imaged, impacting resolution and contrast.
Correct answer is: The pattern of light spread from a point source after passing through the optical system
Q.70 Which of the following best describes 'photon shot noise'?
Noise due to fluctuations in laser power
Noise due to statistical variations in photon arrival
Noise due to electronic interference
Noise due to thermal vibrations of the detector
Explanation - Shot noise arises from the random nature of photon arrival times.
Correct answer is: Noise due to statistical variations in photon arrival
Q.71 Which of these is an essential safety feature for a handheld laser imaging device?
Automatic power ramp‑up
Eye‑protective safety goggles
Built‑in thermal sensor
All of the above
Explanation - Eye protection is mandatory to prevent accidental exposure to laser beams.
Correct answer is: Eye‑protective safety goggles
Q.72 What does the term 'optical path length' refer to in medical imaging?
The physical distance light travels within a medium
The total distance including refraction and scattering events
The distance between the light source and the detector
The depth of the imaging sensor
Explanation - Optical path length accounts for changes in speed and direction as light propagates.
Correct answer is: The total distance including refraction and scattering events
Q.73 Which type of imaging is best suited for detecting early retinal changes in diabetic retinopathy?
Optical coherence tomography (OCT)
X‑ray angiography
Thermal imaging
Ultrasound
Explanation - OCT provides high‑resolution cross‑sectional images of the retina, enabling early detection.
Correct answer is: Optical coherence tomography (OCT)
Q.74 What is the primary advantage of using a 'mode‑locked laser' in OCT?
Higher average power
Short pulse duration for better axial resolution
Simpler tuning
Lower cost
Explanation - Mode‑locked lasers produce broad bandwidth pulses, improving axial resolution.
Correct answer is: Short pulse duration for better axial resolution
Q.75 Which of the following parameters is critical for achieving high‑contrast images in fluorescence microscopy?
Laser beam diameter
Excitation wavelength matching the fluorophore’s absorption peak
Detector quantum efficiency at 300 nm
Sample temperature above 80 °C
Explanation - Optimal excitation maximizes fluorescence emission and contrast.
Correct answer is: Excitation wavelength matching the fluorophore’s absorption peak
Q.76 In photoacoustic imaging, which factor primarily determines the acoustic frequency of the generated signal?
Laser wavelength
Laser pulse width
Acoustic impedance of tissue
Detector bandwidth
Explanation - Shorter pulses generate higher frequency acoustic waves, affecting spatial resolution.
Correct answer is: Laser pulse width
Q.77 Which of the following describes the 'Nyquist criterion' in the context of optical imaging?
The sampling rate must be at least twice the highest spatial frequency to avoid aliasing
The detector must have at least twice the number of pixels as the object size
The optical system should use twice the number of lenses
The laser must emit twice the frequency of the detector
Explanation - Nyquist ensures accurate reconstruction by sampling at sufficient rates.
Correct answer is: The sampling rate must be at least twice the highest spatial frequency to avoid aliasing
Q.78 Which of the following is a major challenge when imaging deep tissue with optical methods?
High optical absorption and scattering
Limited field of view
Low detector sensitivity
All of the above
Explanation - Deep tissues scatter and absorb light, reducing signal strength.
Correct answer is: High optical absorption and scattering
Q.79 What is the advantage of using a 'broadband' light source in OCT?
Improved lateral resolution
Shorter coherence length leading to better axial resolution
Higher power output
Simplified alignment
Explanation - Broadband light reduces coherence length, sharpening depth resolution.
Correct answer is: Shorter coherence length leading to better axial resolution
Q.80 Which component in a fiber‑optic probe is responsible for bending the light path to scan the tissue?
Grating coupler
Micro‑mirror array
Acousto‑optic modulator
Beam splitter
Explanation - Micro‑mirrors deflect the beam across the field for scanning.
Correct answer is: Micro‑mirror array
Q.81 In a spectral‑domain OCT system, why is a 'reference spectrum' subtracted from the measured spectrum?
To remove background detector noise
To isolate the sample signal
To calibrate the wavelength axis
All of the above
Explanation - Subtracting the reference removes system‑specific variations and improves data quality.
Correct answer is: All of the above
Q.82 Which of the following is NOT a factor limiting the speed of OCT imaging?
Detector readout rate
Laser pulse repetition rate
Computational reconstruction time
Sample movement speed
Explanation - The speed is limited by electronics and optics, not by how fast the sample moves.
Correct answer is: Sample movement speed
Q.83 What is 'polarization‑sensitive OCT' (PS‑OCT) used to measure?
The phase shift due to tissue birefringence
The absorption coefficient
The temperature distribution
The electrical conductivity
Explanation - PS‑OCT detects changes in polarization caused by birefringent structures.
Correct answer is: The phase shift due to tissue birefringence
Q.84 Which of the following is a typical application of 'optical biopsy'?
Real‑time detection of cancerous tissues during surgery
Measuring bone density
Mapping skin surface temperature
Recording cardiac activity
Explanation - Optical biopsy uses fluorescence or Raman signatures to identify malignant cells.
Correct answer is: Real‑time detection of cancerous tissues during surgery
Q.85 Which type of detector is most suitable for detecting nanosecond pulses in photoacoustic imaging?
Photodiode
Photomultiplier tube (PMT)
CMOS sensor
Infrared detector
Explanation - PMTs provide high temporal resolution and sensitivity for fast acoustic transients.
Correct answer is: Photomultiplier tube (PMT)
Q.86 In an OCT system, which element is primarily responsible for controlling the axial sampling interval?
Spectrometer dispersion
Laser source bandwidth
Detector pixel spacing
Beam splitter ratio
Explanation - A broader bandwidth yields finer axial sampling due to shorter coherence length.
Correct answer is: Laser source bandwidth
Q.87 Which of the following describes the 'Fourier domain mode‑locked' (FDML) laser?
A laser that locks its frequency to an external reference
A broadband laser that sweeps its wavelength rapidly for OCT
A laser that operates in the frequency domain only
A laser that uses mode‑locking to generate ultra‑short pulses
Explanation - FDML lasers enable high‑speed swept‑source OCT by rapidly tuning the wavelength.
Correct answer is: A broadband laser that sweeps its wavelength rapidly for OCT
Q.88 Which of the following best explains the term 'photothermal therapy' in medical optics?
Using light to heat and destroy cancer cells
Using light to stimulate neuronal activity
Using light to image blood flow
Using light to record EEG signals
Explanation - Photothermal therapy employs lasers to raise local tissue temperature, killing tumor cells.
Correct answer is: Using light to heat and destroy cancer cells
Q.89 What is the typical wavelength of light used in 'visual inspection' for skin surface imaging?
400–700 nm (visible)
700–1300 nm (near‑IR)
3–5 µm (mid‑IR)
10–12 µm (thermal IR)
Explanation - Visible light provides high contrast for surface features in dermatology.
Correct answer is: 400–700 nm (visible)
Q.90 Which of these is a key benefit of using a 'polarization‑maintaining fiber' in a medical imaging system?
It reduces signal loss
It preserves the state of polarization for sensitive measurements
It allows higher power transmission
It increases the bandwidth
Explanation - PM fibers maintain polarization, essential for techniques like PS‑OCT.
Correct answer is: It preserves the state of polarization for sensitive measurements
Q.91 What does the term 'photon flux' refer to?
Number of photons per second per unit area
Speed of photon travel
Energy per photon
Wavelength of photons
Explanation - Photon flux measures how many photons hit an area in a given time.
Correct answer is: Number of photons per second per unit area
Q.92 Which of the following is NOT a typical output parameter in a photoacoustic imaging system?
Acoustic amplitude
Depth of source
Signal frequency spectrum
Optical absorption coefficient
Explanation - Photoacoustic output includes amplitude, depth, and spectrum; absorption coefficient is an input property.
Correct answer is: Optical absorption coefficient
Q.93 What is 'time‑of‑flight' (TOF) measurement used for in optical imaging?
To determine the distance of scattering particles
To calculate the speed of light in tissue
To measure the delay between excitation and emission in fluorescence
To adjust laser wavelength
Explanation - TOF provides depth information by timing how long light takes to return.
Correct answer is: To determine the distance of scattering particles
Q.94 Which type of optical sensor is commonly used for detecting infrared radiation from body surfaces?
Photodiode
CMOS sensor
Microbolometer
Photomultiplier tube
Explanation - Microbolometers detect IR by measuring temperature changes in a resistive element.
Correct answer is: Microbolometer
Q.95 Which component of an optical imaging system typically provides the 'reference beam' in interferometric setups?
Beam splitter
Laser source
Optical fiber
Detector
Explanation - A beam splitter divides the light into reference and sample paths.
Correct answer is: Beam splitter
Q.96 What is the primary function of a 'cooling system' in high‑power laser applications?
To maintain laser wavelength stability
To reduce the thermal noise of the detector
To prevent overheating and maintain beam quality
To increase laser pulse repetition rate
Explanation - Cooling prevents thermal drift and damage in laser components.
Correct answer is: To prevent overheating and maintain beam quality
Q.97 Which of the following describes 'diffuse optical tomography' (DOT)?
An imaging technique that maps the distribution of fluorescent probes in deep tissue
A tomographic reconstruction of light intensity measured after multiple scattering events
A high‑resolution imaging method for surface tissues
A technique that uses X‑ray attenuation to reconstruct images
Explanation - DOT reconstructs 3‑D distributions of optical properties from diffuse measurements.
Correct answer is: A tomographic reconstruction of light intensity measured after multiple scattering events
Q.98 Which of the following is a major advantage of using a 'fiber‑optic probe' for intraoperative imaging?
High mechanical stiffness
Ability to reach deep or narrow anatomical sites
Large field of view
Low cost of operation
Explanation - Fiber probes are flexible, allowing access to hard‑to‑reach areas.
Correct answer is: Ability to reach deep or narrow anatomical sites
Q.99 What is the primary benefit of using 'dual‑band' (visible + NIR) imaging for tumor detection?
It allows imaging of both superficial and deeper tissues simultaneously
It increases the laser power
It reduces the need for contrast agents
It eliminates scattering effects
Explanation - Visible light captures surface details; NIR penetrates deeper, providing complementary information.
Correct answer is: It allows imaging of both superficial and deeper tissues simultaneously
Q.100 Which of the following describes the 'depth of field' (DOF) in an optical system?
The range of depths over which the image remains acceptably sharp
The maximum depth that can be imaged
The depth at which the system focuses best
The distance between the light source and the detector
Explanation - DOF is the interval around the focal plane that stays in focus.
Correct answer is: The range of depths over which the image remains acceptably sharp
Q.101 Which parameter most directly influences the 'penetration depth' of near‑infrared light in biological tissue?
Refractive index mismatch
Absorption coefficient of water
Beam diameter
Laser power
Explanation - Water absorption limits NIR penetration; lower absorption allows deeper imaging.
Correct answer is: Absorption coefficient of water
Q.102 What does 'optical absorption spectroscopy' measure?
The amount of light reflected from a surface
The wavelengths absorbed by a sample
The scattering coefficient of a medium
The phase shift of transmitted light
Explanation - It records how much light is absorbed at each wavelength, revealing chromophore concentrations.
Correct answer is: The wavelengths absorbed by a sample
Q.103 Which of the following is NOT a typical application of optical imaging in dentistry?
Detection of dental caries via fluorescence
Evaluation of pulp vitality using OCT
Thermal imaging of tooth enamel
Imaging of bone marrow
Explanation - Bone marrow imaging is not commonly done with optical methods due to depth limitations.
Correct answer is: Imaging of bone marrow
Q.104 Which optical property does a 'photothermal camera' primarily detect?
Absorbance
Temperature changes induced by light absorption
Fluorescence emission
Polarization state
Explanation - Photothermal cameras sense the heat generated when tissue absorbs light.
Correct answer is: Temperature changes induced by light absorption
Q.105 What is the main advantage of using a 'multimodal' imaging system combining OCT and fluorescence?
Higher resolution images
Simultaneous structural and functional information
Reduced cost
Faster acquisition speed
Explanation - OCT gives depth structure while fluorescence adds biochemical contrast.
Correct answer is: Simultaneous structural and functional information
Q.106 Which of the following best describes the term 'biological safety class' for lasers?
A classification of laser power levels only
A system that categorizes lasers based on potential hazard to skin and eye
A label indicating the wavelength range of a laser
An indicator of the laser’s spectral bandwidth
Explanation - Safety classes (I–IV) reflect the risk posed by laser exposure.
Correct answer is: A system that categorizes lasers based on potential hazard to skin and eye
Q.107 In OCT, what is the 'A‑scan'?
A 2‑D cross‑sectional image
A 1‑D depth profile obtained by scanning a single point
The entire 3‑D image stack
The calibration routine
Explanation - An A‑scan represents the intensity versus depth at a single lateral location.
Correct answer is: A 1‑D depth profile obtained by scanning a single point
Q.108 Which of the following is a primary advantage of using a 'laser‑diode array' in optical imaging?
High power output
Spatially resolved illumination for parallel scanning
Broad spectral output
Simplified alignment
Explanation - Arrays provide multiple beams, enabling faster imaging of extended areas.
Correct answer is: Spatially resolved illumination for parallel scanning
Q.109 What does the term 'photonic crystal fiber' refer to?
A fiber with a periodic micro‑structured cross‑section that guides light via photonic bandgap
A fiber that emits light when excited by a laser
A fiber that contains multiple cores
A fiber used exclusively for thermal imaging
Explanation - Photonic crystal fibers can confine light in hollow cores or with unique dispersion properties.
Correct answer is: A fiber with a periodic micro‑structured cross‑section that guides light via photonic bandgap
Q.110 Which type of laser is commonly used for optical biopsy via Raman spectroscopy?
Nd:YAG at 1064 nm
Ar⁺ laser at 514 nm
Diode laser at 780 nm
CO₂ laser at 10.6 µm
Explanation - Visible lasers such as Ar⁺ provide adequate Raman cross‑sections for tissue analysis.
Correct answer is: Ar⁺ laser at 514 nm
Q.111 What is the significance of 'optical coherence length' in OCT?
The length over which light maintains phase coherence, determining axial resolution
The physical length of the OCT probe
The depth of the imaging system
The distance between the light source and detector
Explanation - Coherence length defines the axial range where interference is significant.
Correct answer is: The length over which light maintains phase coherence, determining axial resolution
Q.112 Which of the following is a primary safety concern when operating a 532 nm laser for intraocular imaging?
Eye damage due to photothermal effects
Acoustic shock
Laser-induced bleeding
Excessive heating of the eye capsule
Explanation - Visible lasers can heat retinal tissues, risking damage; strict safety protocols are required.
Correct answer is: Eye damage due to photothermal effects
Q.113 Which of the following is a typical output format for OCT data?
2‑D B‑scan image
1‑D A‑scan profile
3‑D volumetric dataset
All of the above
Explanation - OCT can produce 1‑D, 2‑D, or 3‑D data depending on the scanning strategy.
Correct answer is: All of the above
Q.114 In fluorescence imaging, what is the purpose of a 'long‑pass filter'?
To block all wavelengths below a certain value, transmitting only longer wavelengths (emission)
To reflect the excitation light back to the source
To narrow the excitation bandwidth
To filter out scattered light
Explanation - Long‑pass filters isolate fluorescence emission from the excitation light.
Correct answer is: To block all wavelengths below a certain value, transmitting only longer wavelengths (emission)
Q.115 Which of the following describes a 'multiphoton excitation' process?
Absorption of a single high‑energy photon
Sequential absorption of two or more lower‑energy photons to reach an excited state
Stimulated emission of a photon
Absorption of a photon followed by immediate re‑emission
Explanation - Multiphoton excitation uses multiple photons to achieve excitation at longer wavelengths.
Correct answer is: Sequential absorption of two or more lower‑energy photons to reach an excited state
Q.116 Which of the following optical imaging techniques is most sensitive to tissue oxygenation changes?
Near‑IR spectroscopy
OCT angiography
Fluorescence lifetime imaging
Thermal imaging
Explanation - Near‑IR spectroscopy detects changes in oxy‑ and deoxy‑hemoglobin absorption.
Correct answer is: Near‑IR spectroscopy
Q.117 What is the 'numerical aperture (NA)' of an objective lens primarily dependent on?
The focal length and aperture diameter
The wavelength of the light source
The detector pixel size
The beam intensity
Explanation - NA = n sin(θ) where n is the refractive index and θ is the half‑angle of acceptance.
Correct answer is: The focal length and aperture diameter
Q.118 Which component is responsible for modulating the intensity of the laser beam in a scanning OCT system?
Acousto‑optic modulator
Polarizer
Diffuser
Beam expander
Explanation - Acousto‑optic modulators rapidly change the beam intensity or deflect the beam for scanning.
Correct answer is: Acousto‑optic modulator
Q.119 Which type of optical imaging is best suited for monitoring wound healing in real time?
Near‑IR fluorescence imaging
X‑ray imaging
MRI
CT
Explanation - Near‑IR fluorescence can detect metabolic changes and angiogenesis during wound healing.
Correct answer is: Near‑IR fluorescence imaging
Q.120 What is the function of a 'diffuse light source' in optical imaging?
To produce coherent light for interference
To create a uniform illumination across the sample
To generate high‑contrast images
To reduce scattering in tissue
Explanation - Diffuse illumination ensures homogeneous lighting, minimizing shadows.
Correct answer is: To create a uniform illumination across the sample
Q.121 Which of the following is a common limitation of optical imaging in diagnosing deep tissue pathologies?
Limited photon flux
High tissue absorption and scattering
Inability to resolve surface structures
Excessive cost
Explanation - Tissue properties impede light penetration, limiting depth resolution.
Correct answer is: High tissue absorption and scattering
Q.122 Which of the following best describes 'spectral unmixing' in fluorescence imaging?
Combining multiple emission spectra to increase brightness
Separating overlapping fluorophore signals based on their spectra
Shifting the excitation wavelength to match the fluorophore
Reducing photobleaching by altering the spectral bandwidth
Explanation - Spectral unmixing deconvolves mixed signals into individual fluorophore contributions.
Correct answer is: Separating overlapping fluorophore signals based on their spectra
Q.123 Which of the following is a key requirement for a laser used in OCT?
High temporal coherence
Low temporal coherence and broad bandwidth
Stable single‑mode operation
High pulse energy
Explanation - Broadband, low‑coherence light provides high axial resolution and minimal interference fringes.
Correct answer is: Low temporal coherence and broad bandwidth
Q.124 Which of the following is a typical application of 'optical coherence elastography' (OCE)?
Measuring tissue stiffness in the eye
Detecting bone fractures
Imaging tumor vasculature
Thermal mapping of skin
Explanation - OCE uses OCT to assess mechanical properties, useful in ophthalmology.
Correct answer is: Measuring tissue stiffness in the eye
Q.125 What does the term 'photodiode responsivity' refer to?
The ratio of output current to incident optical power
The speed of response to light changes
The maximum power the photodiode can handle
The wavelength range over which it operates
Explanation - Responsivity quantifies how effectively a photodiode converts light into electrical signal.
Correct answer is: The ratio of output current to incident optical power
Q.126 Which of the following is a key advantage of using a 'high‑numerical‑aperture objective' in multiphoton microscopy?
Increased imaging depth
Higher laser power delivery
Higher lateral resolution
Lower photobleaching
Explanation - High NA focuses light to a smaller spot, improving resolution and excitation efficiency.
Correct answer is: Higher lateral resolution
Q.127 Which of the following is NOT a component of a standard OCT system?
Broadband light source
Beam splitter
Photodetector array
Electronically tunable filter
Explanation - Standard OCT uses broadband light; tunable filters are not required.
Correct answer is: Electronically tunable filter
Q.128 What is the main difference between 'visible' and 'infrared' light in medical imaging?
Visible light penetrates deeper into tissue
Infrared light is absorbed more strongly by water
Visible light can be used for fluorescence, infrared is mainly for thermal imaging
Infrared light is always safe for skin
Explanation - Visible light excites fluorophores; infrared is used for thermal emission and deeper penetration.
Correct answer is: Visible light can be used for fluorescence, infrared is mainly for thermal imaging
Q.129 Which parameter determines the 'field‑of‑view' of a microscope objective?
Numerical aperture
Lens focal length
Objective diameter
Magnification
Explanation - The objective’s diameter sets the maximum angle of light collection, affecting FOV.
Correct answer is: Objective diameter
Q.130 Which of the following is a major challenge in developing high‑speed OCT systems?
Increasing detector noise
Reducing laser power
Managing data throughput from high‑frame‑rate acquisition
Improving lens quality
Explanation - Fast OCT generates large data volumes requiring real‑time processing and storage.
Correct answer is: Managing data throughput from high‑frame‑rate acquisition
Q.131 What is the function of a 'phase‑shifting interferometer' in OCT?
To increase the coherence length
To measure the phase difference between reference and sample beams
To amplify the optical signal
To stabilize the laser frequency
Explanation - Phase shifting allows precise extraction of interference information for image reconstruction.
Correct answer is: To measure the phase difference between reference and sample beams
Q.132 Which of the following is a common method to reduce speckle noise in OCT images?
Increasing the laser power
Using multiple reference beams
Applying a lateral averaging filter
Shortening the exposure time
Explanation - Speckle is reduced by averaging neighboring pixels, smoothing the image.
Correct answer is: Applying a lateral averaging filter
Q.133 Which of the following is a typical application of 'photoacoustic tomography' (PAT) in clinical settings?
Mapping brain vascular structures
Imaging the gastrointestinal tract
Measuring blood oxygen saturation in the retina
Assessing bone density
Explanation - PAT can non‑invasively assess retinal blood oxygenation by detecting acoustic signals.
Correct answer is: Measuring blood oxygen saturation in the retina
Q.134 Which component is responsible for converting the detected optical signal into an electrical signal in a photodiode?
Photovoltaic effect
Photoelectric effect
Compton scattering
Cherenkov radiation
Explanation - Photovoltaic effect generates current when photons create electron‑hole pairs.
Correct answer is: Photovoltaic effect
Q.135 Which of the following describes the 'bandwidth' of a detector?
The range of wavelengths it can detect
The speed at which it can respond to changes in light intensity
The maximum number of photons it can process per second
The electrical noise level
Explanation - Bandwidth determines how quickly a detector can respond, important for high‑speed imaging.
Correct answer is: The speed at which it can respond to changes in light intensity
Q.136 What is 'optical polarization' primarily used to measure in medical imaging?
The chemical composition of tissue
The orientation and anisotropy of fibrous structures
The temperature of tissues
The electrical conductivity of tissues
Explanation - Polarization changes reveal structural organization, useful for detecting fibrosis.
Correct answer is: The orientation and anisotropy of fibrous structures
Q.137 Which of the following best describes the 'NIR window' (700–1300 nm) for medical imaging?
A range where water strongly absorbs light
A range where hemoglobin absorption is maximum
A range where tissue absorption is minimal, allowing deeper penetration
A range that only allows thermal radiation detection
Explanation - The NIR window has low absorption and scattering, ideal for deep tissue imaging.
Correct answer is: A range where tissue absorption is minimal, allowing deeper penetration
Q.138 Which type of imaging modality uses 'laser speckle contrast' to measure blood flow?
Optical coherence tomography
Laser speckle contrast imaging (LSCI)
Near‑IR spectroscopy
Thermal imaging
Explanation - LSCI analyzes speckle pattern fluctuations to infer blood flow velocity.
Correct answer is: Laser speckle contrast imaging (LSCI)
Q.139 What is the main advantage of using a 'low‑pass filter' in an optical detection system?
To block high‑frequency electronic noise
To allow only long wavelengths through
To reduce the intensity of the laser beam
To narrow the bandwidth of the source
Explanation - Low‑pass filters remove high‑frequency noise components from the detected signal.
Correct answer is: To block high‑frequency electronic noise
Q.140 Which of the following is a typical output metric for photoacoustic imaging?
Optical absorption coefficient
Acoustic pressure amplitude
Spectral reflectance
Fluorescence lifetime
Explanation - Photoacoustic output is measured as acoustic pressure signals generated by light absorption.
Correct answer is: Acoustic pressure amplitude
Q.141 What is 'birefringence' in optical terms?
The difference in absorption of left‑ vs. right‑hand circularly polarized light
The phenomenon where a material has two different refractive indices depending on polarization direction
The ability of a material to reflect light in two directions
The property of a material to scatter light randomly
Explanation - Birefringence arises from anisotropic crystal structures, affecting light propagation.
Correct answer is: The phenomenon where a material has two different refractive indices depending on polarization direction
Q.142 Which of the following is a typical application of 'optical coherence tomography angiography (OCTA)'?
Imaging retinal blood vessels without dye injection
Measuring bone mineral density
Assessing skin surface temperature
Detecting bone fractures
Explanation - OCTA uses motion contrast to visualize vasculature in the retina.
Correct answer is: Imaging retinal blood vessels without dye injection
Q.143 Which of the following is NOT a characteristic of a 'diode laser'?
Compact size
Broad spectral width
High efficiency
Low beam quality compared to solid‑state lasers
Explanation - Diode lasers typically have a narrow spectral width, suitable for coherent applications.
Correct answer is: Broad spectral width
Q.144 What is the purpose of a 'polarizer' in an optical imaging system?
To filter out unwanted wavelengths
To control the polarization state of the light beam
To increase the laser power
To focus the beam onto the sample
Explanation - Polarizers allow selection of a specific polarization, useful in interferometry and imaging.
Correct answer is: To control the polarization state of the light beam
Q.145 Which of the following describes the 'laser safety class I'?
Laser that can be safely operated without any protective equipment
Laser that requires protective eyewear under normal operating conditions
Laser that poses a serious risk even with brief exposure
Laser that can only be used in a controlled laboratory environment
Explanation - Class I lasers are safe under normal operating conditions and pose no eye or skin hazard.
Correct answer is: Laser that can be safely operated without any protective equipment
Q.146 In optical imaging, what is the 'laser spot size' primarily dependent on?
Beam divergence and focal length
Detector pixel size
Wavelength only
Laser power
Explanation - Spot size = beam divergence × focal length; smaller spot yields higher resolution.
Correct answer is: Beam divergence and focal length
Q.147 Which of the following is a key advantage of 'ultra‑short pulse lasers' in optical imaging?
Increased average power
Reduced scattering in tissue
Higher spectral bandwidth leading to improved axial resolution
Lower cost
Explanation - Ultra‑short pulses have broad bandwidth, improving axial resolution in OCT and other techniques.
Correct answer is: Higher spectral bandwidth leading to improved axial resolution
Q.148 What is the role of 'acoustic coupling gel' in photoacoustic imaging?
To focus the laser beam
To improve acoustic transmission between the tissue and the detector
To block external light
To enhance optical absorption
Explanation - Coupling gel eliminates air gaps, facilitating efficient acoustic signal transmission.
Correct answer is: To improve acoustic transmission between the tissue and the detector
Q.149 Which of the following best describes the 'modulation transfer function' (MTF) in imaging systems?
The ratio of the output power to the input power
A measure of how well the system preserves contrast at different spatial frequencies
The amount of light reflected by the system
The spectral response of the detector
Explanation - MTF characterizes the ability of an imaging system to reproduce detail.
Correct answer is: A measure of how well the system preserves contrast at different spatial frequencies
Q.150 Which of the following is NOT a typical component of a photoacoustic imaging system?
Laser source
Acoustic transducer array
Photodiode
Signal amplifier
Explanation - Photoacoustic systems rely on acoustic detection; photodiodes are not used for signal detection.
Correct answer is: Photodiode
Q.151 Which of the following is a common method for reducing photobleaching in fluorescence imaging?
Increasing laser intensity
Reducing exposure time
Using longer excitation wavelengths
Both b and c
Explanation - Shorter exposure times and longer wavelengths reduce photobleaching.
Correct answer is: Both b and c
Q.152 What does 'optical path length mismatch' lead to in an interferometer?
Increased resolution
Reduced interference fringe visibility
Improved signal strength
Enhanced depth penetration
Explanation - Mismatch reduces coherence, causing weaker fringes.
Correct answer is: Reduced interference fringe visibility
Q.153 Which of the following is a major benefit of 'photoacoustic computed tomography' (PACT) over traditional ultrasound imaging?
Higher acoustic resolution
Direct measurement of optical absorption contrast
Lower cost
Simpler equipment
Explanation - PACT detects light absorption indirectly via acoustic signals, providing functional imaging.
Correct answer is: Direct measurement of optical absorption contrast
Q.154 Which optical imaging modality is most suitable for monitoring neuronal activity via hemodynamic changes?
Near‑IR spectroscopy
OCT angiography
Multiphoton microscopy
Thermal imaging
Explanation - Near‑IR spectroscopy can track blood oxygenation changes related to neuronal activity.
Correct answer is: Near‑IR spectroscopy
Q.155 Which component of a laser system typically ensures a stable output power over time?
Beam expander
Temperature controller
Pulse picker
Polarizer
Explanation - Temperature fluctuations affect laser gain; controllers stabilize the output.
Correct answer is: Temperature controller
Q.156 Which of the following is a key challenge in implementing optical imaging for deep brain structures?
High optical scattering in brain tissue
Limited availability of lasers
High detector noise
Low photon flux
Explanation - Brain tissue scatters light strongly, limiting penetration depth.
Correct answer is: High optical scattering in brain tissue