Answers to spec. Q.
What are the nature and properties of X-rays?
X-rays are high-energy electromagnetic waves with wavelengths ranging from 0.01 to 10 nm. They have high penetration power, are ionising, and can be used for medical imaging and therapy.
How is an X-ray spectrum produced, and what methods are used to control beam intensity and photon energy?
X-ray spectra are produced when high-energy electrons strike a metal target (e.g., tungsten) in an X-ray tube. The intensity and energy are controlled by adjusting the tube voltage (kV), and tube current (mA), and filtering out lower-energy X-rays using metal filters.
How are high-energy X-rays used in therapy and low-energy X-rays in diagnosis?
High-energy X-rays (MV range) are used in radiotherapy to destroy cancerous cells. Low-energy X-rays (kV range) are used in diagnostic imaging, such as X-ray radiographs and CT scans.
What is the equation for X-ray attenuation, and what do the terms in I = I0 e−μx represent?
This equation describes the exponential attenuation of X-rays as they pass through matter. I0 is the initial intensity, I is the transmitted intensity, μ is the linear attenuation coefficient, and x is the thickness of the material.
How are X-rays used to image soft tissue, and what role does fluoroscopy play in producing real-time X-ray images using image intensifiers?
Contrast agents (e.g., barium or iodine) are used to enhance soft tissue visibility in X-rays. Fluoroscopy provides real-time moving images using an image intensifier, converting X-ray photons into visible light for continuous monitoring.
What are the techniques of radiography, and how are digital image receptors used?
Techniques include conventional X-ray imaging, computed radiography (CR), and digital radiography (DR). Digital image receptors replace traditional film, allowing for enhanced image processing and storage.
How does a rotating beam X-ray computed tomography (CT) scanner function?
A CT scanner rotates an X-ray beam around the patient, capturing multiple cross-sectional images. A computer reconstructs these into a detailed 3D representation of internal structures.
How are ultrasound waves generated and detected using piezoelectric transducers?
Piezoelectric transducers convert electrical energy into ultrasound waves and vice versa. They generate high-frequency sound waves, which reflect off tissues and return as echoes for imaging.
How is ultrasound used in diagnosis, and what are A-scans and B-scans? Give examples and applications.
A-scans provide 1D distance measuremQQents (e.g., eye measurements in ophthalmology). B-scans create 2D images by converting echo amplitudes into brightness variations (e.g., fetal ultrasound imaging).
What is the significance of acoustic impedance, defined by Z=cρ, in the reflection and transmission of sound waves at tissue boundaries? Why is a coupling medium needed?
Acoustic impedance (Z) determines how much ultrasound is reflected or transmitted at tissue boundaries. A coupling medium (e.g., gel) eliminates air gaps to ensure efficient transmission of ultrasound waves.
How is the Doppler equation Δf / f0 = 2v / c used to study blood flow with an ultrasound probe?
The Doppler effect measures the frequency shift of reflected ultrasound waves from moving blood cells to determine blood flow velocity and direction.
What are the principles of magnetic resonance, and how do precession nuclei, resonance, and relaxation time relate to MRI? How is the Larmor frequency calculated?
MRI exploits the magnetic properties of hydrogen nuclei, which precess in a magnetic field. Radiofrequency pulses cause resonance, and relaxation time differences generate tissue contrast. The Larmor frequency is given by f= 42.6×106 B, where B is the magnetic field strength in Tesla.
How is MRI used to obtain diagnostic information about internal structures?
MRI provides high-contrast images of soft tissues (e.g., brain, muscles, and ligaments) without ionizing radiation by detecting hydrogen nuclei interactions in a strong magnetic field.
What are the advantages and disadvantages of ultrasound imaging, X-ray imaging, and MRI in examining internal structures?
Ultrasound: Safe, real-time imaging, but limited penetration.
X-ray: Quick and detailed images of bones, but ionizing radiation exposure.
MRI: Excellent soft tissue contrast, but expensive and time-consuming.
What are the effects of alpha (α\alphaα), beta (β\betaβ), and gamma (γ\gammaγ) radiation on living matter?
Alpha radiation is highly ionizing but weakly penetrating. Beta radiation is moderately ionizing and penetrates skin. Gamma radiation is highly penetrating but weakly ionizing, potentially causing DNA damage and cancer.
What is the Gray (Gy) unit of absorbed dose and the Sievert (Sv) unit of equivalent dose and effective dose? How is absorbed dose defined?
Gray (Gy): Energy absorbed per kilogram of tissue.
Sievert (Sv): Accounts for radiation type and biological effects.
Absorbed dose: Energy absorbed per unit mass, measured in Gy.
What are the equations for equivalent dose and effective dose, and what do the terms represent?
Equivalent dose: H = DWg , where D is absorbed dose, and Wg is the radiation weighting factor.
Effective dose: E = HWT, where WT is the tissue weighting factor.
How are radionuclides used as tracers to image body parts, with reference to technetium-99m (Tc-99m)?
Tc-99m is a widely used medical tracer that emits gamma rays, enabling imaging of organs like the heart and bones in nuclear medicine scans.
How does a gamma camera function, and what are the principles behind its collimator, scintillation counter, and photomultiplier/CCD?
A gamma camera detects gamma radiation using a collimator to direct photons, a scintillation counter to convert photons into light, and a photomultiplier or CCD to amplify and process the signal.
What is positron emission tomography (PET) scanning, and how is it used in detecting tumours?
PET scanning detects gamma rays emitted from positron-electron annihilation in radiotracers (e.g., FDG). It provides functional imaging of metabolic activity, making it useful for cancer detection.