A 27-year-old woman had a contrast-enhanced CT of the abdomen and pelvis after a road traffic accident. A week later she finds she is 6 weeks pregnant. The medical physicist estimates the fetal dose at about 25 mGy. She is very anxious and asks whether she should terminate the pregnancy. What is the most appropriate counselling?

Reassure: no added malformation risk at this dose

Advise termination for high malformation risk

Advise serial fetal MRI to look for anomalies

Offer amniocentesis to look for radiation damage to the fetus

A 50-year-old man on maintenance haemodialysis had a gadolinium-enhanced MR angiogram of his legs 3 months ago. He now has painful, hard, woody thickening of the skin of his legs and forearms and early contractures of the knees, with no Raynaud's phenomenon and no facial involvement. What is the most likely diagnosis?

Diffuse cutaneous systemic sclerosis

A 52-year-old man developed generalised urticaria and wheeze after iodinated contrast for a CT 2 years ago, which settled with treatment. He now needs an elective contrast-enhanced CT to stage a colonic carcinoma; non-contrast imaging and MRI are not adequate for the question. What is the most appropriate plan?

Premedicate with steroid and antihistamine

Same contrast agent with no precautions

Skin-prick test with the contrast agent first

Same agent at half the usual dose

Radiation physics, contrast and radiotherapy

14 NEET-PG practice questions on Radiation physics, contrast and radiotherapy, part of Radiology. The first 14 are below; the first 5 with answers and explanations (tap Show answer after you have chosen), the rest in Learn with a free account.

Question 1 · Hard
A 52-year-old interventional cardiologist who has worked in a catheterisation lab for 20 years without protective eyewear develops a posterior subcapsular cataract. The radiation safety officer makes four statements: 1. Cataract is a deterministic (tissue) effect with a threshold dose. 2. The severity of a stochastic effect increases with the dose received. 3. Radiation-induced leukaemia is a stochastic effect. 4. ICRP has reduced the occupational dose limit for the lens to 20 mSv per year, averaged over 5 years. Which statements are correct?
1. A2 and 3 only
2. B1, 3 and 4 only
3. C1 and 4 only
4. D1, 2 and 3 only
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Answer: B · 1, 3 and 4 only
Statements 1, 3 and 4 are correct. Deterministic effects such as cataract, skin erythema and sterility appear only above a threshold, and their severity rises with dose. Stochastic effects, cancer and heritable effects, have no assumed threshold: their probability rises with dose but their severity does not, so statement 2 is false. In 2011 ICRP lowered the lens limit for workers from 150 mSv to 20 mSv per year averaged over 5 years, which makes lead glasses and ceiling shields important in cath labs.
- A: Includes the false claim on stochastic severity and leaves out cataract as deterministic.
- C: Leaves out leukaemia as a stochastic effect, which is true.
- D: Includes the false claim on stochastic severity and leaves out the lens limit.
Question 2 · Hard
A 27-year-old woman had a contrast-enhanced CT of the abdomen and pelvis after a road traffic accident. A week later she finds she is 6 weeks pregnant. The medical physicist estimates the fetal dose at about 25 mGy. She is very anxious and asks whether she should terminate the pregnancy. What is the most appropriate counselling?
1. AAdvise termination for high malformation risk
2. BAdvise serial fetal MRI to look for anomalies
3. COffer amniocentesis to look for radiation damage to the fetus
4. DReassure: no added malformation risk at this dose
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Answer: D · Reassure: no added malformation risk at this dose
A fetal dose below 50 mGy has not been associated with an increased risk of malformations, growth restriction or pregnancy loss; such effects need doses of about 100-200 mGy or more. A single diagnostic CT of the abdomen and pelvis usually gives well under this level, so the dose is not a reason to consider termination. The possible rise in childhood cancer risk is very small. She should be counselled honestly and supportively, with the dose estimate documented.
- A: At about 25 mGy there is no increase in malformation risk to justify termination.
- B: Serial MRI is unnecessary; routine anomaly scanning is enough.
- C: Amniocentesis cannot detect radiation effects and carries its own risk.
Question 3 · Medium
A 50-year-old man on maintenance haemodialysis had a gadolinium-enhanced MR angiogram of his legs 3 months ago. He now has painful, hard, woody thickening of the skin of his legs and forearms and early contractures of the knees, with no Raynaud's phenomenon and no facial involvement. What is the most likely diagnosis?
1. ADiffuse cutaneous systemic sclerosis
2. BCalciphylaxis
3. CLipodermatosclerosis
4. DNephrogenic systemic fibrosis
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Answer: D · Nephrogenic systemic fibrosis
Nephrogenic systemic fibrosis is a fibrosing disorder of the skin and deeper tissues that follows gadolinium-based contrast in patients with severe kidney failure (eGFR below 30 or on dialysis). Free gadolinium released from less stable agents is thought to trigger fibrosis. It starts in the limbs and spares the face, which helps to separate it from systemic sclerosis. It is prevented by avoiding gadolinium or using the more stable macrocyclic agents at the lowest dose in such patients.
- A: Systemic sclerosis usually begins with Raynaud's phenomenon and involves the face.
- B: Calciphylaxis causes painful necrotic ulcers with livedo, not diffuse woody thickening.
- C: Lipodermatosclerosis affects the lower legs in venous disease, not the forearms.
Question 4 · Hard
A 52-year-old man developed generalised urticaria and wheeze after iodinated contrast for a CT 2 years ago, which settled with treatment. He now needs an elective contrast-enhanced CT to stage a colonic carcinoma; non-contrast imaging and MRI are not adequate for the question. What is the most appropriate plan?
1. APremedicate with steroid and antihistamine
2. BSame contrast agent with no precautions
3. CSkin-prick test with the contrast agent first
4. DSame agent at half the usual dose
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Answer: A · Premedicate with steroid and antihistamine
A previous moderate allergic-like reaction raises the risk of another, so for an elective study that truly needs contrast the usual plan is premedication with corticosteroids (for example oral prednisolone 50 mg at 13, 7 and 1 hour before) and an antihistamine 1 hour before, with a different low-osmolar agent. Premedication reduces but does not abolish the risk, so the scan is done with resuscitation drugs and trained staff at hand. The reaction and agent are recorded clearly in his notes.
- B: Repeating the same agent without precautions risks a similar or worse reaction.
- C: Skin and test doses do not predict allergic-like reactions to contrast.
- D: These reactions are not dose dependent, so halving the dose does not protect him.
Question 5 · Medium
During a portable chest X-ray in the ICU, a staff nurse is standing 1 metre from the X-ray tube. She steps back to 2 metres before the exposure. By how much does her radiation dose rate change, taking the tube as a point source?
1. AIt falls to one quarter
2. BIt falls to one half
3. CIt is not changed
4. DIt falls to one eighth
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Answer: A · It falls to one quarter
Radiation from a point source follows the inverse square law: intensity is proportional to 1/distance squared. Doubling the distance from 1 m to 2 m gives (1/2)², so the dose rate falls to one quarter. Time, distance and shielding are the three practical ways to reduce dose, and distance is the cheapest. Staff not needed during a portable exposure should stand at least 2 metres away or behind a shield.
- B: One half would mean dose falls in simple proportion to distance, not with its square.
- C: Moving away always reduces exposure from a point source.
- D: One eighth would need a cube law; radiation follows the square.
Question 6 · Easy
In which phase of the cell cycle are cells most sensitive to ionising radiation?
1. AEarly G1 phase
2. BLate S phase
3. CG2 and M phases
4. DG0 (resting) phase
Answer and explanation in LearnFree account
Question 7 · Medium
A 48-year-old woman is having a contrast-enhanced CT of the abdomen. One minute after the iodinated contrast injection she develops diffuse urticaria, wheeze and hoarseness; BP is 78/50 mmHg and pulse 128/min. What is the first drug to give?
1. AIntravenous pheniramine
2. BIntravenous hydrocortisone
3. CNebulised salbutamol
4. DIntramuscular adrenaline
Answer and explanation in LearnFree account
Question 8 · Medium
A 58-year-old woman with type 2 diabetes takes metformin 1 g twice daily. Her eGFR is 25 mL/min/1.73 m², and she needs a contrast-enhanced CT for suspected renal cell carcinoma. What should be done with her metformin?
1. AContinue it at the same dose
2. BWithhold it, recheck renal function at 48 hours
3. CStop it permanently after the scan
4. DStop it one week before and one week after the scan
Answer and explanation in LearnFree account
Question 9 · Medium
A 55-year-old woman treated with chemoradiation for carcinoma of the cervix 14 months ago now has painless bright red rectal bleeding and tenesmus. Colonoscopy shows pale rectal mucosa with many fine telangiectasias and no tumour. What is the main mechanism of this condition?
1. AObliterative endarteritis causing ischaemia
2. BRecurrence of tumour in the rectal wall
3. CImmune-mediated chronic inflammatory colitis
4. DDeath of crypt stem cells during treatment
Answer and explanation in LearnFree account
Question 10 · Medium
A 48-year-old woman at a regional cancer centre has squamous cell carcinoma of the cervix that extends to the pelvic side wall and causes left hydronephrosis. What is the standard treatment?
1. ANeoadjuvant chemotherapy, then surgery
2. BChemoradiation, then intracavitary brachytherapy
3. CRadical hysterectomy with pelvic lymph node dissection
4. DIntracavitary brachytherapy alone
Answer and explanation in LearnFree account
Question 11 · Medium
A 64-year-old diabetic man with chronic kidney disease (eGFR 28 mL/min/1.73 m²) needs a contrast-enhanced CT of the chest and abdomen to stage a suspected lung cancer. What is the most effective measure to reduce his risk of contrast-associated kidney injury?
1. AIV furosemide after the scan
2. BPeri-procedural IV isotonic saline
3. CHigh-osmolar contrast at a lower dose
4. DOral N-acetylcysteine without fluids
Answer and explanation in LearnFree account
Question 12 · Easy
A newly appointed radiographer at a district hospital asks about her occupational dose limit. What is the effective dose limit for radiation workers, averaged over 5 years?
1. A1 mSv per year
2. B20 mSv per year
3. C50 mSv per year
4. D150 mSv per year
Answer and explanation in LearnFree account
Question 13 · Medium
A 30-year-old man with a pure seminoma of the testis is counselled about radiotherapy after orchidectomy. While teaching on the case, the radiation oncologist makes four statements: 1. Hypoxic tumour cells are more radiosensitive than well-oxygenated cells. 2. Lymphocytes are the most radiosensitive cells in the blood. 3. Melanoma is a highly radiosensitive tumour. 4. Seminoma is a highly radiosensitive tumour. Which statements are correct?
1. A2 and 4 only
2. B1 and 3 only
3. C1, 2 and 4 only
4. D3 and 4 only
Answer and explanation in LearnFree account
Question 14 · Easy
A resident starting work in the cardiac catheterisation lab is given a small badge to wear at chest level under his lead apron, which is sent away every quarter for reading. What is this device?
1. AScintillation detector
2. BThermoluminescent dosimeter
3. CIonisation chamber survey meter
4. DGeiger-Müller counter
Answer and explanation in LearnFree account

Radiation physics, contrast and radiotherapy

During a portable chest X-ray in the ICU, a staff nurse is standing 1 metre from the X-ray tube. She steps back to 2 metres before the exposure. By how much does her radiation dose rate change, taking the tube as a point source?

In which phase of the cell cycle are cells most sensitive to ionising radiation?

A 48-year-old woman is having a contrast-enhanced CT of the abdomen. One minute after the iodinated contrast injection she develops diffuse urticaria, wheeze and hoarseness; BP is 78/50 mmHg and pulse 128/min. What is the first drug to give?

A 58-year-old woman with type 2 diabetes takes metformin 1 g twice daily. Her eGFR is 25 mL/min/1.73 m², and she needs a contrast-enhanced CT for suspected renal cell carcinoma. What should be done with her metformin?

A 55-year-old woman treated with chemoradiation for carcinoma of the cervix 14 months ago now has painless bright red rectal bleeding and tenesmus. Colonoscopy shows pale rectal mucosa with many fine telangiectasias and no tumour. What is the main mechanism of this condition?

A 48-year-old woman at a regional cancer centre has squamous cell carcinoma of the cervix that extends to the pelvic side wall and causes left hydronephrosis. What is the standard treatment?

A 64-year-old diabetic man with chronic kidney disease (eGFR 28 mL/min/1.73 m²) needs a contrast-enhanced CT of the chest and abdomen to stage a suspected lung cancer. What is the most effective measure to reduce his risk of contrast-associated kidney injury?

A newly appointed radiographer at a district hospital asks about her occupational dose limit. What is the effective dose limit for radiation workers, averaged over 5 years?

A resident starting work in the cardiac catheterisation lab is given a small badge to wear at chest level under his lead apron, which is sent away every quarter for reading. What is this device?