Radiation in diagnosis and treatment: Practice Questions

Which of the following describes the purpose of using barium meal as a contrast medium in X-ray radiography?

A monochromatic X-ray beam is directed through a tissue sample. If the half-value thickness (HVT) of the tissue is 1.8 cm, what is the linear attenuation coefficient \( \mu \) of this tissue?

A barium meal (contrast medium) is used to image the stomach. If the linear attenuation coefficient of the barium contrast is \( 5.2 \text{ cm}^{-1} \) and the soft tissue is \( 0.25 \text{ cm}^{-1} \), find the ratio of X-ray intensity passing through 0.5 cm of barium compared to 0.5 cm of soft tissue.

Which medical imaging technique produces cross-sectional images by rotating an X-ray source and multiple detectors around the patient?

An X-ray beam of initial intensity \( I_0 \) passes through a material. If the intensity is reduced to 6.25% of its original value, how many half-value thicknesses (HVTs) of the material were used?

State the purpose of using an artificial contrast medium, such as a barium meal, during an X-ray radiographic examination of the soft tissues in a patient's digestive system.

Technetium-99m is frequently used as a diagnostic tracer. Explain why its short physical half-life and emission of only gamma rays are ideal characteristics for minimizing biological risk while ensuring high-quality images.

In Computed Tomography (CT), explain why the scanner must collect multiple projections from many different angles to reconstruct a cross-sectional image of the body.

X-ray Attenuation and Half-Value Thickness

A monochromatic X-ray beam is used to image a section of soft tissue. The linear attenuation coefficient \(\mu\) for this tissue at the specific X-ray energy is \(0.231\text{ cm}^{-1}\).

(a) Calculate the half-value thickness (HVT) of the soft tissue.

(b) If the initial intensity of the X-ray beam is \(I_0\), determine the remaining intensity (as a fraction of \(I_0\)) after it has passed through \(9.0\text{ cm}\) of this tissue.

(c) State one reason why the linear attenuation coefficient of bone is significantly higher than that of soft tissue for the same X-ray energy.

X-ray Attenuation in Composite Tissues
A patient's arm consists of multiple tissue types that attenuate X-rays differently. A narrow monochromatic X-ray beam of initial intensity \( I_0 \) passes through 4.0 cm of muscle followed by 2.0 cm of bone. The linear attenuation coefficients are \( \mu_m = 0.18 \text{ cm}^{-1} \) for muscle and \( \mu_b = 1.20 \text{ cm}^{-1} \) for bone.
(a) Calculate the total attenuation factor (the ratio \( I/I_0 \)) for the X-ray beam after passing through both layers.
(b) If the bone is replaced by an equal thickness of fat (\( \mu_f = 0.14 \text{ cm}^{-1} \)), calculate the new ratio of transmitted intensity.
(c) Explain, in terms of the atomic composition of the tissues, why bone has a much higher linear attenuation coefficient than fat or muscle for diagnostic X-ray energies.