INI CET Radiology Flashcards

24 sample cards from the Radiology deck

Sampled from the end of the deck, so these are different cards from the ones shown on the syllabus page.

1. What is CT pulmonary angiography (CTPA) used for, and what is the key positive finding?

   CTPA is the first-line investigation for pulmonary embolism. The key finding is a filling defect (clot) within a contrast-opacified pulmonary artery; large central clots may straddle the bifurcation ('saddle embolus').

2. What is the basic physical principle of MRI signal generation?

   Hydrogen protons align with a strong static magnetic field; a radiofrequency pulse tips them out of alignment, and as they relax back they emit RF signals. Spatial encoding by gradient coils and Fourier transformation create the image.

3. Define T1 and T2 relaxation in MRI.

   T1 (longitudinal/spin-lattice) relaxation is recovery of longitudinal magnetization along the main field. T2 (transverse/spin-spin) relaxation is decay of transverse magnetization due to loss of phase coherence among protons.

4. How do fat, water, and CSF appear on T1- and T2-weighted MRI?

   On T1: fat is bright, water/CSF is dark. On T2: water/CSF is bright, fat is intermediate-to-bright. A simple rule: 'water is dark on T1 and bright on T2.'

5. What contrast agent is used in MRI, and what is a major safety concern?

   Gadolinium-based contrast agents shorten T1 (causing enhancement on T1-weighted images). A major concern is nephrogenic systemic fibrosis in patients with severe renal impairment; gadolinium also crosses the placenta and is generally avoided in pregnancy.

6. What MRI sequence is most sensitive for acute ischaemic stroke and how does infarct appear?

   Diffusion-weighted imaging (DWI) is most sensitive; acute infarcts show restricted diffusion appearing bright on DWI and dark on the corresponding ADC map within minutes to hours.

7. Why is MRI superior to CT for musculoskeletal soft tissue, and what is a key contraindication?

   MRI provides excellent soft-tissue contrast for cartilage, ligaments, tendons, menisci, marrow, and tumours without ionizing radiation. A key contraindication is certain ferromagnetic implants/devices (e.g., some pacemakers, cochlear implants, intraocular metallic foreign bodies).

8. What is the basic physical principle of diagnostic ultrasound imaging?

   A transducer emits high-frequency sound waves (typically 2-15 MHz) into tissue; reflected echoes at tissue interfaces are detected and timed to construct an image. Echo strength depends on acoustic impedance differences between tissues.

9. What is the trade-off between transducer frequency and ultrasound image quality?

   Higher-frequency probes give better spatial resolution but less tissue penetration (used for superficial structures); lower-frequency probes penetrate deeper with lower resolution (used for deep/abdominal imaging).

10. Define the ultrasound terms 'anechoic', 'hyperechoic', and 'acoustic shadowing'.

    Anechoic = no internal echoes, appears black (e.g., simple fluid/cyst). Hyperechoic = bright echoes (e.g., gallstones, calcification). Acoustic shadowing = a dark band behind a strongly reflecting/absorbing structure such as a gallstone or bone.

11. What is the Doppler effect and how is it used in ultrasound?

    The Doppler effect is the change in frequency of reflected sound from moving objects (red blood cells). It is used to assess blood flow direction and velocity (colour and spectral Doppler), e.g., for vascular stenosis, DVT, and fetal circulation.

12. What are the components of the obstetric biophysical profile and what parameters are measured for fetal dating?

    Biophysical profile: fetal tone, gross body movements, breathing movements, amniotic fluid volume, and a non-stress test (heart rate reactivity). Early dating uses crown-rump length (most accurate in the first trimester); later parameters include biparietal diameter, head/abdominal circumference, and femur length.

13. Define the most commonly used radiopharmaceutical in nuclear medicine and its key physical properties.

    Technetium-99m (Tc-99m). It emits 140 keV gamma photons (ideal for gamma cameras), has a 6-hour physical half-life, is produced from a molybdenum-99/Tc-99m generator, and can be tagged to many compounds for organ-specific imaging.

14. How does a gamma (Anger) camera form an image?

    Gamma photons emitted by an in-vivo radiopharmaceutical pass through a collimator (selecting direction), strike a sodium iodide (NaI(Tl)) scintillation crystal producing light, which photomultiplier tubes convert and localize electronically to build a planar image of tracer distribution.

15. How does SPECT differ from planar gamma imaging, and how does it relate to PET?

    SPECT (single-photon emission CT) rotates gamma camera heads around the patient to reconstruct 3D tomographic images from single gamma-emitting tracers (e.g., Tc-99m). PET uses positron-emitting tracers (e.g., F-18 FDG) detected by coincidence detection of paired 511 keV annihilation photons, giving higher resolution and quantification.

16. List the three cardinal principles of radiation protection (ALARA).

    Time (minimize exposure time), Distance (maximize distance from the source, using the inverse square law), and Shielding (use lead/concrete barriers). ALARA = keep dose 'As Low As Reasonably Achievable.'

17. What is interventional/image-guided drainage, and which modalities guide it?

    Percutaneous placement of a catheter or needle into a fluid collection (e.g., abscess, biliary, urinary) under imaging guidance. Ultrasound, CT, and fluoroscopy are the main guidance modalities; ultrasound is real-time and radiation-free, CT gives precise deep targeting.

18. What are common minimally invasive tumour ablation techniques and their mechanisms?

    Radiofrequency ablation (RFA) and microwave ablation destroy tissue by heat-induced coagulative necrosis; cryoablation destroys tissue by freezing. They are image-guided alternatives to surgery for small tumours (e.g., liver, kidney, lung).

19. What is transarterial chemoembolization (TACE) and its main indication?

    TACE delivers chemotherapy directly into the tumour's feeding artery combined with embolic particles that block blood supply, concentrating the drug and inducing ischaemia. It is a key treatment for unresectable hepatocellular carcinoma.

20. Differentiate the two main delivery methods of radiation therapy.

    External beam radiotherapy (teletherapy) delivers radiation from an external source (e.g., linear accelerator) aimed at the target. Brachytherapy places sealed radioactive sources within or adjacent to the tumour (e.g., cervical, prostate cancer), giving a high local dose with rapid falloff.

21. What machine delivers most external beam radiotherapy and what does it produce?

    The linear accelerator (LINAC) accelerates electrons to high energy; these strike a target to produce high-energy (megavoltage) X-ray photons, or the electron beam itself is used to treat superficial tumours.

22. What are the '4 R's' of radiobiology underlying fractionated radiotherapy?

    Repair (of sublethal damage in normal cells between fractions), Reassortment/Redistribution (cells move into radiosensitive phases), Repopulation (regrowth of normal tissue), and Reoxygenation (hypoxic tumour cells become better oxygenated and more radiosensitive).

23. Define the target volumes used in radiotherapy planning (GTV, CTV, PTV).

    GTV (gross tumour volume): visible/palpable tumour. CTV (clinical target volume): GTV plus a margin for microscopic spread. PTV (planning target volume): CTV plus a margin for setup error and organ/patient motion to ensure the prescribed dose is delivered.

24. What imaging is used for radiotherapy treatment planning, and what is the SI unit of absorbed dose?

    A planning CT (often fused with MRI/PET) defines anatomy and target volumes and provides electron-density data for dose calculation. The SI unit of absorbed radiation dose is the gray (Gy), where 1 Gy = 1 joule per kilogram.

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