Medical Imaging Modalities Flashcards
MRI
CT
CT
MRI
CT
What is an angiograph? How is a digitally subtracted angiograph (DSA) different?
An angiograph is a radiograph with a contrasting agent injected into blood vessels to visualise these blood vessels. An iodine-containing compound (‘contrasting agent’) is injected into an artery. Iodine is used because it has a high atomic number and thus absorbs x-rays efficiently. Its atomic number is much higher than the atoms that comprise most of the body, and is thus able to provide contrast with the tissues of the body.
In digitally subtracted angiographs (DSAs), a series of radiographs are taken before and over several seconds after the injection. In the first few seconds the arteries will be visualised, and after several seconds the veins, as the contrast agent is carried with the blood through the arteries, capillaries and then veins. By digitally subtracting the pre- from the post-injection radiographs, only the vessels will appear in the image.
Magnetic resonance angiogram
Positron Emission Tomography
PET is used for the assessing of metabolism of tissues. Radioactive isotopes with short half-life that emit gamma rays coupled to compounds and injected into the vein, and specific tissues take up these compounds. Gamma ray detector then record the gamma rays emitted from the patient’s tissues.
In which region of the body can some blood vessels be soon on a ‘plain’ radiograph? Explain why.
In a plain radiograph most blood vessels cannot be seen as they have similar radiodensity to surrounding tissue. However, in the thorax, the lungs are much less radiodense, so the large blood vessels can be seen in a plain radiograph.
