Radiologic Tests

8/10/2019 Radiologic Tests

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RADIOLOGIC TESTS

Radiologic Tests

Introduction to Radiologic Tests

Learning to evaluate radiographic tests is essential for excellent patient care. A thorough knowledge

of anatomy and pathology is essential in this pursuit.

Computed Tomography (CT) Scan

CT is a more sensitive x-ray detection system which creates slice images through the body. The x-

ray tube and detectors rotate around the patient, and a computer system manipulates the data. The

data can be reconstructed to create axial (transverse), sagittal, coronal, and 3 -D views.

When looking at an axial CT, imagine you are standing at the patient's feet looking toward their

head. Different window settings on the computer allow you to view certain structures better (e.g.

bone window lung window) IV and oral contrast can be used to evaluate arteries, veins and

gastrointestinal structures in more detail.

Fluoroscopy

A continuous beam of x-rays passes through the patient and gives a moving, real-time image;

basically a moving x-ray. Used in gastrointestinal barium and other contrast studies, angiography,

and most interventional radiology procedures. Commonly used intra-operatively in orthopedic

surgery and neurosurgery.

Magnetic Resonance Imaging (MRI)

The patient is placed within the bore of a powerful magnet that passes radio waves though

the body in a particular series of very short pulses. Each pulse causes a responding pulse to

be emitted from the patient. A computer manipulates the data which produces an image.

Contrast may be used to evaluate certain conditions. Different sequences include T1 in

which fluid appears dark and T 2 in which fluid appears bright white.

The benefits to the MRI include no radiation exposure and it provides more soft tissue

detail.

The cons to MRI include expense, contraindicated if the patient has metal hardware

implanted or a pacemaker takes longer than a CT, motion interference can distort images,

claustrophobic or severely anxious patient may not be able to tolerate scan, morbidly obese

may not be able to fit in the scanner.


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Radionuclide Imaging (Nuclear Imaging)

Uses radiolabeled isotopes (radionuclide) attached to normal physiologic chemical substances to visualize

particular living organs and tissues. An image is obtained because the isotope emits gamma rays for a brief

period of time which are detected by special cameras.

Technetium-99m (99mTc): Most commonly used nuclide. Used in ionic form to detect a Meckel

diverticulum, or attached to organic phosphate for a bone scan. It can even be attached to patient's own

RBCs or WBCs.

Positron Emission Tomography (PET) Scan: Uses short-lived positron emitting isotopes most commonly

attached to a glucose analogue to detect areas of increased metabolic activity. Most common use is

evaluating for staging solid tumors and evaluating metastasis. PET can be fused with a CT scan to precisely

localize lesions.

Ultrasound (US)

Very high frequency sound is directed into the body from a transducer placed in

contact with the skin. The sound is reflected by tissue to produce echoes picked up

from the same transducer and converted into an electrical signal which produces 2 -D

or 3 -D images.

Ultrasound is a less expensive test that does not expose the patient to radiation. The test

is useful for obstetrical, gynecological, pediatric, and testicular conditions, determining

cystic (black) vs. solid (grey) structures. US can also produce moving images and can

be done at the bedside.

Ultrasound takes longer than a CT scan, results are operator dependent, it is not useful

for bone or lung since these entities almost completely absorb the ultrasound beam.

Doppler US:Sound reflected from a mobile structure shows a variation in frequency that corresponds to

the speed of movement. The shift in frequency can be turned into an audible signal (e.g. fetal heartbeat)

Flow can also be shown as the frequency changes depending on the direction of the flow in relation to the

transducer. This is illustrated by colors on the screen with red signifying flow toward the transducer andblue signifying flow away from the transducer.

Examples of US exams: Echocardiography, obstetrical US , premature infant head US , suspected

abdominal aortic aneurysm (AAA) or deep vein thrombosis (DITT) , gallbladder US , trauma (focused

assessment with sonography for trauma or FAST exam) , pelvic US , breast US , testicular US , carotid US


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X-rays

There are five basic densities on an x-ray

Air- Will appear black

Bone-Will appear white

Fat- Denser than air but less dense than soft tissues

Soft Tissue-Denser than fat but less dense than bone

X-rays are absorbed to a variable extent as they pass

through the body. This difference in absorption

produces an image. The projection is described by the

path of the x-ray beam (e.g. in a PA or posteroanterior

film the x-ray beam went through the patient's back

initially)

An x-ray will only produce 2 -D images, therefore perpendicular views may need to be obtained. Always

consider x-ray before a CT or MRI.

Specific Radiologic Tests

Abdominal CT

Commonly used with oral and IV contrast to evaluate trauma, appendicitis, pancreatitis, diverticulitis,

kidney stones(without contrast), and determine stages of cancer.

Abdominal Ultrasound

Used to rapidly evaluate the liver , gallbladder (gallstones, cholecystitis) , appendix, pancreas,

and abdominal aortic aneurysms.

Abdominal X-rays (Kidney Ureter Bladder or KUB)

The KUB is an x-ray of the abdomen taken in anteroposterior or AP direction. It is commonlyordered in patients complaining of abdominal pain.

An abdominal x-ray can help identify foreign bodies, ileus, malrotation, small bowel obstruction

with air-fluid levels, and volvulus.

It can also detect perforation with "free-air" under the diaphragm or within structures air should

not normally be (e.g. intestinal wall or biliary tract) but the upright chest x-ray is the better

test.


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Arthrography

Imaging following the injection of contrast (iodinated or air) into a joint to highlight the soft

tissue structures by coating their surfaces. It is used most often to define intra-articular structures or

to confirm intra-articular needle placement when joint aspiration is performed. Typically, contrast

material is injected in a joint using fluoroscopic guidance; the joint is then subjected to further imaging with either

CT or MRI.

Barium Enema

A barium enema is a test in which barium sulfate is placed into the patient's rectum in order to evaluate

the colon. X-rays are taken which will outline the location of the barium in the colon.

Patients undergo a bowel prep the night before with laxatives such as polyethylene glycol in order to "clean

out" the patient thoroughly for the examination, as is also done before procedures such as colonoscopies.

Barium Swallow

The patient is given barium to swallow while the esophagus is imaged via fluoroscopy. Used to

evaluate esophageal pathology , aspiration, and swallowing abnormalities.

In a modified barium swallowdifferent consistencies of barium are swallowed by the patient. X-rays are

taken to monitor for aspiration. This helps determine what types of foods are safe for the patient to eat.

Bone X-ray

X-rays of the bones are ordered primarily to detect fractures. They may also help diagnose osteomyelitis

which may be visualized as an elevation of the periosteum.

Chest CT

Allows for detailed images of the chest cavity. Indications may include pneumonia, lung nodules,

pneumothorax, pulmonary embolismand rib fractures.


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Chest X-ray

A chest x-ray is used to evaluate patients with complaints of shortness of breath, cough,

chest pain, fever, and hemoptysis as well as abnormal physical exam findings of the lungs

or chest wall.

It is typically ordered in patients who have suffered trauma and to verify correct placement

of lines and tubes.

The image will include the lungs, heart, mediastinum and upper portion of the abdomen.

A chest x-ray can reveal numerous pathology including aortic dissection, congestive heart

failure, emphysema, free air under the diaphragm from perforations, lung masses,

pneumonia, and a pneumothorax.

Posteroanterior (PA)

The posteroanterior orPAview is the standard projection for chest x-ray , such that the beam passes from

the patient 's back to their front. A patient will be standing for this x-ray

Anteroposterior (AP)

In an anteroposteriororAPview the beam passes from front to back. This view cannot be used to estimate

heart or mediastinum size. It is most often obtained on patient 's that cannot sit up or stand and is

sometimes called a "portable view" since the x-ray department may need to travel to the patient's room

using a mobile x-ray machine. An AP will typically be of poorer quality

Lateral

A lateral chest x-rayis often obtained to get a 3 -D picture and provide a more precise location

of an abnormality such as a mass or pneumonia. A pleural effusion may be seen with up to as

little as 50 mL of fluid is present.

Decubitus

A lateral decubitus chest filmis one in which the patient is asked to lie on a specific side in

order to assess for a pleural effusion. The pleural fluid, if present, will "layer out" and can be

seen when as little as 175 mL of pleural fluid is present.

Chest CT

A chest CT can be used to more definitively evaluate for cancerous lesions and abnormal lymphadenopathy

interstitial lung disease, and pulmonary emboli.


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Dual-energy X-ray Absorptiometry (DEXA) Scan

A test used to measure bone density and diagnose osteoporosis. Typically performed in women > 65

years. The T -score compares the patient's bone density to the optimal peak bone density

Osteopeniais diagnosed with a T-score < -1. Osteoporosisis diagnosed with a T-score


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Upper Gastrointestinal Series with Small Bowel Follow Through (UGI and SBFT)

Serial x-rays are taken after barium is swallowed by the patient, usually at approximately 30

minute intervals. The barium appears white on the x-ray. Abnormalities will show as filling

defects.

Used to evaluate swallowing, gastroesophageal reflux, the esophagus, stomach, and small

intestines. Sometimes gas is used as a second contrast agent. This is called an air-barium double-

contrast study and allows for more mucosal definition.

Voiding Cystourethrogram (VCUG)

Test that uses x-rays to evaluate the urinary system during voiding. The bladder is filled with

contrast and vesicoureteral reflux is diagnosed if there is retrograde flow to the kidneys.

Radiologic Tests

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