Radiology and Endoscopy of the GI Tract
Radiology
Plain Film x-ray
yields a two dimensional image; quickly and easily obtained and read
four densities can be easily distinguished:
air black
fat dark grey
water/soft tissue light grey
metal/bone white
what are they good for?
abnormal calcifications: stones, calcified gall bladder, etc
abnormal air spaces: air is normal in colon; abnormal most other places
air under diaphragm
Þ
GI perforation
small bowel obstructions are usually obvious as distensions (normal diameter is ~ 2-2.5 cm)
not good for distinguishing borders of soft tissue structures; however, barium can provide contrast
barium contrast can delineate masses, ulcers
air/barium contrast: barium, then fill with air: good way to study the mucosa
barium enema is method of choice to study the colonic mucosa
CT Computed Tomography
can distinguish subtle differences in density
Þ
separate soft tissue (i.e. organ from neoplasm)
separate water from soft tissue
IV and oral contrast can be used to provide additional accuracy
better 3D localization
Þ
can be used for image guided procedures (i.e. biopsy guidance - dont want to hit anything important)
can detect: ulcers, neoplasms; colitis; appendicitis; cysts; abcesses; hemangioma; metastasis in liver, etc
Ultrasound
reletively inexpensive; allows realtime, multiplanar imaging; safe because no radiation used; doppler imaging can provide information on flow
cannot penetrate bone or air; low frequency needed to penetrate deep, but high frequency offers better picture
Nuclear Radiology
a radiologically tagged substance is given to a patient (often IV); scanning for gamma rays elucidates structures
hepatosplenic imaging: technetium sulfur colloid is injected and ingested by Kuppfer cells and splenic macrophages
can detect metastasis to the liver, focal nodular hyperplasia, identification of residual splenic tissue post-op
hepatobiliary studies (cholescintigraphy): substance used is absorbed by the kidney and rapidly excreted in the bile
good for detecting cholecystitis, post-op biliary disruption
esophageal motility studies, gastric emptying studies: barium swallow
PET scanning
: Positron Emission Tomography; very useful, but expensive and difficult to administer
MRI
(Magnetic Resonance Imaging): proton NMR based on water molecules
multiplanar, no x-rays
excellent contrast, but sensitive to motion (i.e. of gut, heart)
newer, faster imaging techniques make MRI more useful
angiography without the use of contrast (needed in CT) is possible