Diagnostic Imaging Techniques Flashcards
X-Rays - how it works
photons are directed at a particular region via lead shunts and the waves pass through structures in the body, attenuating as they pass through to the film
Attenuation, low to high
(appears black) air, fat, water, bone (appears white)
What do you do if you need to see structures that don’t attenuate x-rays very well?
Use a contrast agent
What studies is iodine used for in the context of contrast agents? Why is it used
intra-arterial and intravenous studies to see kidneys, bladder, ureters; used because it has a high molecular weight and is naturally excreted
What studies is barium sulfate used for in the context of contrast agents? Why is it used?
visualization of bowel loops; high density, insoluble salt that is removed from system leaving a thin coating on the bowels that is passed with bowel movements
What is barium commonly used in combination with?
air - via ingesting fizzy particles or enema
What is subtraction angiography?
to visualize structures that may be difficult to see with one image, one x-ray is taken and then a contrast agent is administered before a second image is taken
the first image is inverted to created a negative image, and then a computer combines the images to visualize the contrast only
How are X-rays interpreted?
X-ray tube is placed 1 m from film
anterior is closest to tube, posterior is closest to film
right side of image is on the left (anatomical position)
Chest Radiograph position
patient is upright, posteroanteriorly (PA) positioned (chest to film)
Abdominal Radiograph position
AP supine (laying down, face up)
Chest Radiograph features
should show lungs, cardiomediastinal contour, diaphragm, ribs, and peripheral soft tissues
Ultrasound
high frequency sound waves emitted by piezoelectric material are sent through the body and they bounce back off of internal organs; the waves coming back are received by the piezoelectric material and a computer at generates an image
What position is a patient placed when a small bowel obstruction is expected?
erect AP
Doppler Ultrasound
a variation of regular ultrasound used to determine flow, direction, and velocity within a vessel
Computed Tomography (CT scan)
series of images taken in the axial plane (horizontal slices), and are combined by a computer to produce a final image
CT image interpretation (3)
anatomical position (right side of patient is on the left)
uppermost border of image is anterior
view from bottom to top
Magnetic Resonance Imaging (MRI)
protons of H-atoms (of water molecules) are oriented randomly throughout the body and can be thought of a magnets; a strong magnet orients all of the H-atoms the same way before a radio wave is emitted, sending the H-atoms back to their ground states
when the H-atoms emit energy to return to their ground state, the signal is read by a computer to provide an image
T1 weighted v T2 weighted MRI
difference b/w pulse sequence and scanning parameters
T1: dark fluid/bright fat
T2: bright fluid/intermediate signal for fat
MRI image interpretation (4)
anatomical position
uppermost border of image is anterior
view bottom to top
can use paramagnetic contrast agents (weakly magnetic)
Nuclear Medicine Imaging
visualize structures using a radiopharmaceutical and a gamma camera (that produces the image)
The radioisotopes used for NMI must: (3)
1) have a reasonable half-life
2) have easily measured gamma rays
3) have as low energy deposition as possible in patient tissues
What radiopharmaceutical is used to visualize bone?
Technetium-99m w/ methylene diphosphonate
Positron Emission Tomography (PET scan)
detects positron emitting radionuclides that are proton rich; commonly used to detect cancer
What is a commonly used radionuclide used in PET scans?
Fluorodeoxyglucose (labelled with F-18) - taken up by tissues actively metabolizing glucose (produces hot spots i.e. cancer)
Advantage to CT scan
can compress or extend gray scale to visualize bone, soft tissues, and viscera
