Diagnostic Imaging and Testing

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Diagnostic Imaging and Testing


Sally A. Perkins and Lawrence J. Kusior



Objectives


At the completion of this chapter the reader should be able to do the following:


1. Identify the various diagnostic imaging and laboratory tests for a given medical condition


2. Explain test preparation and procedures to patients undergoing diagnostic evaluation


3. Relate risks and side effects of specific procedures


4. Justify which medical conditions can be diagnosed by specific diagnostic imaging or laboratory testing


5. Apply appropriate pre-MRI testing health questions to patients


6. State normal values for urine and blood


7. Differentiate radiation levels of assorted diagnostic tests



Introduction


Diagnostic imaging refers to special images produced by radiologists and radiology technicians to determine specific medical conditions. The type of imaging, ordered by a physician, is based on the patient’s symptoms and location of those symptoms. The images, which provide an internal view of anatomical structures, ensure that a more accurate diagnosis and treatment plan can be implemented. Radiologists are medical doctors who have completed residency training in radiology (often in a specific area of radiology). Radiologists read and interpret the images and provide the treating physician with a report of any abnormal findings.


Diagnostic testing refers to medical tests that are performed primarily in a laboratory setting, and include blood, urine, and cardiovascular tests. A medical technologist analyzes the blood and/or tissue and then sends a report to the physician. A cardiac technician or sometimes a nurse will administer special cardiac tests, which are read and interpreted by the physician or a cardiologist.



Diagnostic Imaging


Radiography: X-rays


An x-ray is a form of electromagnetic radiation that, when passed through a patient, allows viewing of internal structures. The x-ray beam is absorbed to different extents by the various body tissues. Less dense tissue appears darker because the radiation is not absorbed in these structures. For example, the lungs appear dark because air does not absorb radiation. Fat is gray, and bone and calcium are light or white (Figure 3-1). Sometimes


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FIGURE 3-1 An anterior–posterior (AP) x-ray demonstrating a Jones fracture of the fifth metatarsal and a bipartite medial sesamoid in the left foot.


KEY POINTS


INFORMED CONSENT


Before performing any diagnostic imaging or tests, patients must be made aware of risks associated with the test and agree to submit to testing.


contrast agents such as barium or iodine are introduced intravenously and are used for gastrointestinal imaging. Contrast agents generally show on the radiograph as white or light. Most of the x-ray beam is absorbed by the tissues or is scattered, while a small amount passes through the body part to the receptor, creating the image. The image may be developed to film or, in the case of digital radiographs, may be saved and viewed on a computer.


Because a radiograph is a two-dimensional picture of a three-dimensional body part, x-rays from several different angles may be administered in succession. Views are often named for the direction in which the x-ray beam passes through the body. For example, an image taken with the x-ray beam passing from the anterior to posterior side of the patient is called an AP view, whereas an image taken from back to front is called a posterior–anterior view (PA view). A view shot from the side is called a lateral view. Other views may be named for the person who first produced that particular view or perhaps for the place where it was first used.


During the procedure, the patient is asked to lie still and not move until the image has been taken. Depending on the type of radiograph taken, patients may be asked to hold their breath so that the image is not blurred by movement of the rib cage. The test is painless and lasts only a few seconds, whereas an entire series of x-rays may last 10 minutes. More than one view may be taken of an area.


Radiographs are ordered when there is the possibility of a fracture, dislocation, boney abnormality or deformity, tumor, arthritis, bone cancer, foreign object, infection, or dental caries. For structures that cannot normally be imaged (blood vessels or hollow organs), a contrast medium may be introduced either by mouth or intravenously. These agents will show up as white inside the hollow organ or blood vessel to allow the visualization of these structures on the image. Because metal absorbs x-rays it shows up as white, obscuring anything behind it; for this reason jewelry and even clothing in or near the area to be exposed to x-rays may need to be removed so that the image taken is clear and not distorted. Because the image is two-dimensional, it is important to remember that anything in the path of the x-ray beam, including items not necessarily in the patient, shows up on the image.



Risks or Side Effects


Radiographs should not be taken of women who are pregnant, because the radiation may have an effect on the fetus. It is imperative that pregnancy status be determined by a blood test, or through a comprehensive menstrual history, before radiography is allowed. Any time that radiation is used there is a slight chance of developing certain types of cancer such as leukemia and melanomas. Physicians try to minimize exposure to x-rays by using the least amount of radiation necessary and by screening patients on the basis of criteria such as the Ottawa ankle rules. The Ottawa ankle rules are used to determine whether radiographs should be taken after an ankle injury. There are also criteria for the knee. Criteria for the ankle/foot are based on location of bone pain, tenderness, and weight-bearing ability. Criteria for the knee are slightly different, with consideration of age (over 55 yr), patella and/or fibular head tenderness, ability to flex the knee, and weight-bearing ability. Table 3-1 illustrates the amount of radiation introduced into the body for common diagnostic tests, including x-ray radiographs.




Radionuclide Bone Scan


A radionuclide bone scan is a nuclear imaging test involving the injection of a short-lived radionuclide to assess abnormalities of the bones. Patients scheduled for such a scan will be asked to remove clothing and wear a gown for the procedure. A radionuclide tracer, which emits gamma rays, and is attracted to increased metabolic activity is injected into the brachial vein in the cubital fossa of the elbow. The patient may feel some warmth as the tracer circulates throughout the body. The technician providing the injection typically wears a radiation-protective lead vest and gloves when administering the injection. After a period of time (30 min–2 h) to allow the isotope to circulate in the body, the patient is moved to the examination room and placed supine on a table. The patient lies still as a special camera moves around him/her. The camera identifies gamma rays, high levels of which indicate increased metabolic activity in bone, and are viewed on a computer or radiograph. Images are taken at various time intervals, revealing the rate at which the tracer is absorbed in the bone.


Areas of inflammation or injury to a bone will appear dark on a bone scan; these are called “hot spots.” Lighter areas on the bone scan show normal tissue and bone (Figure 3-2).


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FIGURE 3-2 A bone scan showing uptake in the tarsal cuneiform bones, suggesting a possible stress reaction.

Bone scans are used to identify stress fractures, bone infections, bone cancer, and arthritis. The same nuclear technology may be applied to other structures such as the thyroid and heart, or to identify abscesses or tumors. Nuclear medicine may also be combined with computed tomography to allow visualization of the structure(s) in slices.




Fluoroscopy


Fluoroscopy is a type of radiography that can be performed when the clinician wants to see a “live” image to determine the size, shape, and movement of tissue. It is not as detailed as an x-ray–based radiograph. Fluoroscopes are commonly found in the athletic training clinics of large universities and professional athletic venues; they are a quick and noninvasive means of determining whether a fracture has occurred, thereby warranting further studies. Fluoroscopic evaluation also assists in return-to-play decisions because the image can be taken with the patient in a weight-bearing position, thus allowing the diagnosis to be made immediately. Clothing should be removed from the area to be examined. Women should notify the technician if they might be pregnant and may be asked to undergo urinalysis or a blood test before fluoroscopy to rule out pregnancy.


The patient stands or sits next to the machine and the technician lines up the machine and the structure to be evaluated (Figure 3-3). Radiation is allowed to pass through the skin, creating light and shadows that are viewed on a computer screen and can be printed. Dense areas such as bone will appear white on the film, and less dense areas such as the lungs will appear darker.


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FIGURE 3-3 A mobile fluoroscope. (Courtesy OEC Diasonics, Inc. In Frank ED, Long BW, Smith BJ: Merrill’s atlas of radiographic positioning and procedures, ed 11, St. Louis, 2010, Elsevier.)

The fluoroscope can be used to look at blood flow, tumors, fractures, organs, foreign bodies, and some soft tissue. It can also be used to assist with biopsy, injections, catheter insertion, and even pacemaker insertion.




Computed Tomography Scan


A computed tomography (CT) scan combines specialized high-resolution radiographs with computers to give better visualization of internal structures in cross-section or three dimensions (3D). It works by passing rotating beams of x-rays through the patient and measuring the transmission at thousands of points. The images may be seen individually as a series of cross-sectional “slices,” but 3D images can be produced by a computer (Figure 3-4). CT exposes a patient to about 10 to 100 times the radiation of an x-ray. Depending on the structures to be examined, the patient may be injected with a contrast dye or asked to consume a barium or other contrast solution at various intervals before or during the CT scan. Contrast agents are usually the same iodinated agents used in other imaging studies. The patient may feel some warmth as the contrast dye is administered intravenously.


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FIGURE 3-4 A computed tomography (CT) machine. The table moves in and out of the machine as the camera circles around. (From Frank ED, Long BW, Smith BJ: Merrill’s atlas of radiographic positioning and procedures, ed 11, St. Louis, 2010, Elsevier.)

The patient must lie very still on a table that moves in and out of an open tube. At times the patient must hold his or her breath so that the images produced are clear. There is a whirring sound when the machine is operating, and it can sometimes be very noisy. The test is painless and lasts from 15 minutes to 1 hour, depending on the structures to be examined.


CT scans are performed to look at cross-sections of internal organs, bone, soft tissue, and blood vessels (Figure 3-5).


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FIGURE 3-5 Computed tomography (CT) demonstrates the shoulders of a patient lying supine. The scapula, spine, and sternum are all visible in white.



Positron Emission Tomography Scan


A positron emission tomography (PET) scan is ordered by a physician to examine the cell metabolism and biochemistry of tissue and organs. PET scans can identify abnormal metabolic activity before it becomes apparent on a CT scan or by magnetic resonance imaging (MRI). The patient is administered a glucose-based radionuclide injection intravenously, or tablets by mouth, depending on the suspected condition. The patient is placed on a table and the imaging unit takes pictures of specific areas of the body. The patient needs to remain still at all times and may be asked not to breathe for short periods of time so that the image produced is clear. The table will move the patient in and out of the machine, similar to a CT scan. At times the machine may move around the patient. The glucose-based radionuclide is absorbed by the area of abnormal metabolic activity and will appear dark on the body image view, similar to a bone scan, or as bright colors on 3D images (Figures 3-6 and 3-7).


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FIGURE 3-6 Positron emission tomography (PET) image demonstrating a healthy pelvis. The patient is in the supine position. The bright color at the top of the image is the bladder.

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FIGURE 3-7 A, Positron emission tomography (PET) image taken to evaluate a patient with a history of melanoma on the scalp. The scan shows no definite evidence of recurrence. B, Another image taken 6 months later shows profound and widely disseminated hypermetabolic metastases throughout the body. (From Frank ED, Long BW, Smith BJ: Merrill’s atlas of radiographic positioning and procedures, ed 11, St. Louis, 2007, Elsevier.)

This imaging mode is used to identify certain types of cancer, thyroid conditions, infections, and bleeding and to evaluate kidney function.




Magnetic Resonance Imaging


An MRI scan (also termed an “MR”) is a test that applies a magnetic field to the body. The magnetic field aligns the body’s atoms in such as way that, when released, they generate radio waves. The frequency of the emitted radio waves is related to the location and chemical environment of the atoms (Figure 3-8). A computer analyzes the data and creates an image. This image provides detailed information about organs, soft tissue, bones, tumors, bleeding, or infection. MRI scans are used to identify tumors, musculoskeletal injuries, soft tissue conditions, fractures, and bleeding (Figure 3-9).


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FIGURE 3-8 A magnetic resonance imaging (MRI) unit. (Courtesy General Electric Medical Systems, Milwaukee, Wis. In Frank ED, Long BW, Smith BJ: Merrill’s atlas of radiographic positioning and procedures, ed 11, St. Louis, 2007, Elsevier.)

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Sep 3, 2016 | Posted by in MUSCULOSKELETAL MEDICINE | Comments Off on Diagnostic Imaging and Testing

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