Marilyn Baird; Week 4 MED1022; Anatomy
Attenuated beam is white component, least attenuated is black component. Fluoroscopy is low dose, continuous x-ray output giving a live x-ray image. Good to observe and record dynamic anatomy and pathology eg contrast enema
DSA is digital subtraction angiography. Is the basis for vascular radiology.
Nuclear medicine uses material with a short radioactive half life tagged to a specific compound, injected into patient. Used for bone scans, V/Q scans, cardiac imaging, thyroid and PTH imaging, liver, spleen and gallbladder imaging; uses radiotracer which emits gamma rays, detected by a gamma camera to form the image.
PET scans give images about metabolic activity by using radioisotopes tagged with glucose, increased activity correlates with neoplasia/infection. Can be overlaid on MRI to give complete picture.
CT is slices, a rotating fan-beam of X rays is moved through a patient, data collected opposite to origin of the beam. Density is calculated. Is very rapid
MRI applies magnetic field, radiofrequency increases the energy of protons, relaxation of protons gives off radiofrequency energy which is detected by electromagnetic coils and converted to electrical energy. Energy released by protons differs according to the density of the protons and their environment. T1 is bright signal for fat, blood, calcium- proteinaceous fluid, gadolinium contrast opacification. T2 is a bright signal, fluid based eg CSF, bile, urine, oedema or fat. No radiation, only downsides are cost, availability, acquisition times, prone to motion/breathing.
Ultrasound detects returning sound waves. Disadvantages are it is operator dependant, images are selective, adipose results in poor image quality, cannot penetrate bone.
Contrast has problems with allergic reactions, nephrotoxicity, worse with metformin/dehydration
Choice of imaging should be related to particular test, risk/benefit, cost/benefit.