FMGE 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 CT findings differentiate an extradural (epidural) from a subdural haematoma?

   Extradural haematoma is biconvex (lens/lentiform shaped), does not cross suture lines, and is often arterial (middle meningeal artery). Subdural haematoma is crescent-shaped (concave), crosses suture lines but not the midline, and is usually venous (bridging veins).

2. What is the difference between high-resolution CT (HRCT) and standard CT of the chest?

   HRCT uses thin (~1 mm) sections with a high-spatial-frequency (sharp) reconstruction algorithm to assess fine lung parenchymal detail (interstitial lung disease). Standard CT uses thicker contiguous slices, often with IV contrast, for masses, mediastinum, and vessels.

3. What is the role of IV contrast timing (phases) in CT of the abdomen?

   Arterial phase (~25-35 s) shows hypervascular lesions and arteries; portal venous phase (~60-70 s) gives best parenchymal (liver) enhancement and most lesion detection; delayed/excretory phase (several minutes) assesses the collecting system and washout (e.g., cholangiocarcinoma).

4. What is the basic physical principle of MRI?

   Hydrogen protons align with a strong static magnetic field; a radiofrequency pulse tips them; as they relax back they emit RF signals. Spatial encoding via gradient coils and Fourier transform reconstruction produces images based on tissue proton density and relaxation times (T1, T2).

5. How do fluid (e.g., CSF) and fat appear on standard T1- versus T2-weighted MRI?

   On T1-weighted images fat is bright and fluid/CSF is dark. On T2-weighted images fluid/CSF is bright and fat is intermediate-to-bright. Mnemonic: 'WW2' — Water is White on T2.

6. What is the FLAIR sequence in MRI and what is its main use?

   FLAIR (Fluid-Attenuated Inversion Recovery) is a T2-weighted sequence that suppresses (nulls) the bright CSF signal, making periventricular and cortical lesions (e.g., MS plaques, oedema, infarcts) more conspicuous against dark CSF.

7. What MRI sequence detects acute cerebral infarction earliest, and how does it appear?

   Diffusion-weighted imaging (DWI) detects acute ischaemia within minutes. Restricted diffusion appears bright on DWI and dark on the corresponding ADC map, due to cytotoxic oedema.

8. What are the absolute contraindications/safety hazards for MRI?

   Ferromagnetic foreign bodies (especially intra-ocular metal), most older pacemakers/ICDs, cochlear implants, certain aneurysm clips, and projectile risk from ferromagnetic objects. Gadolinium contrast is relatively contraindicated in severe renal failure (risk of nephrogenic systemic fibrosis).

9. Why is MRI superior to CT for musculoskeletal soft-tissue and marrow imaging?

   MRI offers superior soft-tissue contrast, directly imaging cartilage, ligaments, tendons, menisci, and bone marrow (e.g., marrow oedema, occult fractures, osteomyelitis) without ionizing radiation, whereas CT excels at cortical bone detail.

10. What is the basic physical principle of ultrasound imaging?

    A transducer's piezoelectric crystals emit high-frequency sound pulses (~2-15 MHz); echoes returning from tissue interfaces of differing acoustic impedance are timed and converted to an image. Stronger reflectors appear brighter (hyperechoic).

11. What is the trade-off between high- and low-frequency ultrasound transducers?

    Higher-frequency probes give better spatial resolution but poorer penetration (used for superficial structures). Lower-frequency probes penetrate deeper but give lower resolution (used for deep abdominal/obstetric imaging).

12. Explain the ultrasound terms anechoic, hyperechoic, hypoechoic, and acoustic shadowing.

    Anechoic = no internal echoes, appears black (e.g., simple cyst, fluid). Hyperechoic = brighter than surrounding tissue. Hypoechoic = darker than surrounding tissue. Acoustic shadowing = dark band behind a strongly reflecting/absorbing structure (e.g., gallstone, calculus).

13. What is the classic ultrasound triad of acute cholecystitis?

    Gallstones (echogenic foci with posterior shadowing), gallbladder wall thickening (>3 mm), and a sonographic Murphy's sign (maximal tenderness over the gallbladder under the probe), often with pericholecystic fluid.

14. What does a 'comet-tail' artifact / posterior acoustic enhancement indicate on ultrasound?

    Posterior acoustic enhancement is increased brightness deep to a fluid-filled (low-attenuation) structure like a cyst, helping confirm it is fluid. Comet-tail/ring-down artifacts indicate small highly reflective interfaces (e.g., cholesterol crystals, B-lines in the lung).

15. How is gestational age estimated on first-trimester obstetric ultrasound, and what is the most accurate parameter?

    Crown-rump length (CRL) is the most accurate parameter for dating in the first trimester. Later, measurements include biparietal diameter (BPD), head circumference (HC), abdominal circumference (AC), and femur length (FL).

16. What is a radiopharmaceutical, and which radionuclide and decay are most used in diagnostic nuclear medicine?

    A radiopharmaceutical is a radioactive tracer combining a radionuclide with a targeting carrier molecule. Technetium-99m is most used: it decays by isomeric transition emitting a 140 keV gamma photon, with a ~6-hour half-life, ideal for gamma camera imaging.

17. How does a gamma camera (scintillation/Anger camera) form an image?

    Gamma photons from the patient pass through a collimator (selecting direction), strike a sodium iodide (NaI(Tl)) scintillation crystal producing light flashes, which photomultiplier tubes convert to electrical signals; positional logic maps where each photon originated to build a planar image.

18. What is SPECT and how does it differ from planar gamma imaging?

    SPECT (Single-Photon Emission Computed Tomography) rotates one or more gamma cameras around the patient to acquire multiple projections, then reconstructs 3D tomographic (cross-sectional) images—improving contrast and localization over 2D planar scintigraphy.

19. What is the Seldinger technique used in image-guided procedures?

    A method for safe vascular/cavity access: puncture with a needle, pass a guidewire through the needle, remove the needle leaving the wire, then advance a catheter/sheath over the wire. It underlies angiography, central line and drain placement.

20. Give examples of minimally invasive image-guided therapies and the imaging used to guide them.

    Examples: percutaneous tumour ablation (radiofrequency, microwave, cryoablation), transarterial chemoembolization (TACE) of liver tumours, angioplasty/stenting, uterine fibroid embolization, and image-guided biopsy/drainage—guided by ultrasound, CT, or fluoroscopy/DSA.

21. What are the four 'R's of radiobiology underlying fractionation in radiation therapy?

    Repair (of sublethal damage in normal cells), Reassortment/Redistribution (of cells into radiosensitive phases), Repopulation (of normal tissue), and Reoxygenation (of hypoxic, radioresistant tumour cells). Fractionation exploits these to spare normal tissue while killing tumour.

22. How does ionizing radiation kill cells in radiation therapy, and what is the SI unit of absorbed dose?

    Radiation causes DNA damage (chiefly double-strand breaks), directly and indirectly via free radicals from water radiolysis, leading to cell death (mainly mitotic/apoptotic). The SI unit of absorbed dose is the gray (Gy) = 1 joule per kilogram.

23. What is the difference between teletherapy (external beam) and brachytherapy?

    Teletherapy delivers radiation from an external source at a distance (e.g., linear accelerator/cobalt-60). Brachytherapy places radioactive sources in or adjacent to the tumour (interstitial or intracavitary, e.g., cervical cancer), exploiting the inverse-square fall-off to spare surrounding tissue.

24. What is the purpose of CT simulation and treatment planning in radiotherapy?

    CT simulation acquires the patient in the treatment position to delineate target volumes (GTV/CTV/PTV) and organs at risk. Planning software then computes beam arrangements and dose distributions (e.g., 3D-CRT, IMRT) to maximize tumour dose while respecting normal-tissue tolerance, verified before delivery.

What this deck covers

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