X-ray Generation and Radiography Questions and Answers

Answer: B

The contrast agent is barium, given as barium sulphate.

Barium has a high atomic number, so it absorbs X-rays strongly and outlines the lumen of the gut. Barium sulphate is almost insoluble and is not absorbed from the gut, so it can be swallowed (barium swallow and meal) or given as an enema with little toxicity.

Iodinated contrast is mainly used for blood vessels and the urinary tract, and water-soluble iodine agents are used in the gut only when a perforation is suspected. Gadolinium is an MRI contrast agent. Saline has no X-ray contrast.

Answer: A

The early sign is calcification deposits.

Clustered microcalcifications, especially fine, pleomorphic or linear branching ones, are often the first and only mammographic sign of ductal carcinoma in situ and early invasive cancer. Calcium absorbs X-rays strongly, so even tiny deposits show up clearly at the low tube voltages used in mammography.

Mammography is an X-ray projection technique and does not show blood flow, which is assessed with Doppler ultrasound or contrast MRI. Tissue elasticity is measured with elastography. Bone density is measured by DEXA, not mammography.

Answer: C

The modality used is fluoroscopy.

Fluoroscopy gives continuous, real-time X-ray images. With iodinated contrast injected through the catheter, it lets the interventionist watch the guidewire, the balloon and the stent move inside the coronary or peripheral artery during angioplasty.

CT and MRI produce cross-sectional images after acquisition and are not used to guide catheters routinely. MRI is also incompatible with most catheter laboratory equipment. PET shows metabolic activity, takes minutes to acquire and is not a guidance tool.

Answer: C

The maximum photon energy is set by the tube voltage (kVp).

An electron accelerated through a peak potential of V kilovolts arrives at the anode with a kinetic energy of V keV. The most energetic bremsstrahlung photon it can produce carries all of that energy, so the spectrum ends at E max = kVp in keV. A 100 kVp tube produces photons up to 100 keV.

Tube current (mA) and exposure time change the number of photons, not their maximum energy. Filtration removes low-energy photons and raises the average energy, but it does not change the upper limit.

Answer: D

Beam hardening results in an increased average photon energy.

A diagnostic X-ray beam is polyenergetic. As it passes through the patient, low-energy photons are absorbed more readily than high-energy ones, so the beam that remains is weighted towards higher energies. It is said to become 'harder', with a higher mean energy.

A harder beam penetrates more, not less, so 'reduced penetration' is the reverse. Low-energy photons are removed, not increased. Noise depends on the number of photons reaching the detector and is not the defining effect of hardening.