Radiology Basics

All information contained in this section was primarily obtained from Radiology 101: The Basics and Fundamentals of Imaging by William Erkonen .

Plain radiographs

Basics

Lower density structures absorb less of the administered x-ray beam.

So,

--Air and fat are BLACK.

--Bone, metal, and calcium are WHITE.

--All other tissues are varying shades of gray, depending on the density of the structure.

Common views: PA, AP, Lateral, Oblique views. This indicates the direction of the beam, e.g. in a PA view the beam is directed from posterior to anterior. Portable views thus have to usually be AP.

Contrast Media

Contrast Media is used to distinguish between soft tissue or organ densities. High density contrast agents are used (usually injected IV) to enhance the target areas, increasing their density and making them appear more white. IV contrast agents are used for fistulograms, draining sinuses, hysterosalpingograms, and other such studies.

Barium studies are indicated for GI pathology visualization. The high-density contrast medium can be ingested orally, or admisistered via enema or intestinal tube. When air is introduced with barium, it is called a double-contrast study .

These studies are better tolerated and less invasive than endoscopy, and are usually the first-step in evaluating bowel pathology.

Gastrograffin is a water-soluble iodinated compound and can be ingested as a solution. It can be employed in the same manner as barium, but give poorer contrast because it is less dense. Indications include suspected perforation(where barium may be contraindicated) and gallbladder stones/tumors(oral cholecystogram). This compound is hypertonic, and can be toxic if leaked into the tracheobronchial tree.

IV iodinated compounds are used in angiography, CT, and for urinary tract visualization(e.g. excretory urogram or Intravenous Pyelogram, IVP).

Computed Tomography (CT)

Q. Who was ultimately responsible for the advent of CT technology?

A. The Beatles!!

Believe it or not, a fair amount of credit must go to the best band ever for being primary financial support for Electric Musical Instruments, Ltd, the engineers of which developed the basis of CT technology in the 1970s.

Basics:

CT images are produced by a combination of x-rays, computers, and detectors. The x-ray tube in the housing of the CT scanner emits pencil-thin beams of x-rays through each anatomic slice of the patient. The x-rays strike detectors(instead of film) and subsequently is converted through computer software into cross-sectional images.

Indications:

3D correlation of plain films, trauma, intracranial hemorrhage, abdominal injury, foreign body detection, primary and metastatic tumors of the liver, kidney, brain, lung, and bone, lymphomas, as well as staging of neoplasms(nodal spread).

Magnetic Resonance Imaging (MRI)

Basics:

MRI involves the imaging of protons, specifically hydrogen. There are many hydrogen atoms in fat, so fat is very bright. Bone has little H+ in it, so it is black.

T1 —fat is white, gray soft tissue detail quality really high, resolution really great; good for viewing anatomy.

T2 —water is white, soft-tissue has less contrast, fat is more gray. This is good for viewing pathology, in which necrosis, effusion, hemorrhage, or other process which has more water will light up with better contrast to normal tissues.

Indications :

MRI detects small changes in soft tissues, with better contrast than CT, so it is good for rotator cuff tears, meniscal tears, and other soft tissue imaging.

Gadolinum creates improved contrast between tissues (esp. on T1); good for tumors, infections, and acute stroke; safer than iodinated contrast.

MRA shows blood flow to be bright, as opposed to black on normal MR imaging. This is an ideal way to visualize flow in cerebral and carotid vessels, using gradient echo pulse sequence. The advantages of this technique include that it is non-invasive, requires no catheters, needles, or iodinated contrast agents.

Ultrasound (US)

Basics:

Short bursts of high-frequency sound waves (1-10MHz) are intermittently broadcast by a transducer. The analog sound waves reflected back are digitized and converted into and image.

Solid tissues —more homogeneous and WHITE.

Ex: Liver, spleen, kidney (not calyces).

Cystic structures —Hypoechoic, BLACK.

Ex: Cysts (renal, liver, etc.), gallbladder, bladder.

Pros : Safe, fast, inexpensive, very portable, multiple plane imaging possible, including obliques.

Cons : Requires technical skill/operator dependent, not good for lung and bone.

Indications:

Fetal monitoring/imaging, GB/kidney pathology, ovarian, endometrial pathology, testicular pathology, breast imaging for cysts.

Nuclear Medicine (NM)

Basics:

Small amounts of radionuclides are administered, tagged to a variety of compounds that can selectively be taken up by a particular organ to be studied. The radioactive emissions from the administered compounds are then detected and recorded by a special camera with a sodium iodide crystal, and an image is made.

Indications :

Interventional Radiology (IR)

Examples of procedures—angiography, thrombolysis, balloon angioplasty, PICC placement, Percutaneous Biliary drainage/stenting, IVC filter placement, and more.

ACE-active drugs:

Ace-inhibitors —Accupril, Aceon, Altace, Capopril, Mavik, Monopril, Prinivil, Univasc, Vasotec, Zestril.

Combo Ca2+ Channel Blockers —Lexxel, Lotrel, Tarka

Ace +Diuretic —Prinizide, Uniretic, Vasoretic, Zestoretic

ARB's —Atacand, Avapro, Cozaar, Diovan, Micardis

ARB/Diuretic Combo —Avalide, Hyzaar