Chapter 18. Radiology/Imaging

In situations without imaging capacity, clinicians need to rely more on the history, physical exam, observation with repeat exams, and, in some cases, exploratory surgery.

The World Health Organization (WHO) lists what they consider the essential diagnostic imaging equipment worldwide (Table 18-1).1 This varies with the four levels of hospital capabilities (see Table 5-1 in Chapter 5, Basic Equipment).

Limited Imaging Situations—the Hot Light

Even if radiology is available, it may be intermittent and the images may be of poor quality. Film, rather than digital images, may be the norm.

To help illuminate dark areas of the film, make a "hot light." Using a lamp with a 25-watt regular lightbulb, take off the shade and slip a tin can with both ends cut out over the shade's support wires. The can should fit tightly so the wires support the can. If this is not the case, cut the can lengthwise and wind tape around it so that it sits securely on the shade supports. Then take a piece of heavy cardboard, aluminum foil, or thin metal and cut a 2- to 3-inch-diameter hole in the center. Lay this on top of the can and tape it in place. If using cardboard, be careful that it doesn't get too hot and burn. When you need to see a dark area on the film, turn on the light and hold the film over it—but not too close or it will begin to burn. Don't bother trying to use flashlights (too diffuse a beam) or pen lights (too narrow).

Light Boxes

Light boxes (view boxes) to view radiological images may be scarce. View boxes can be made (Figs. 18-1 and 18-2) or the film can be read without one. Methods to view films without a view box include the following:

• Hold the radiograph up to a light source such as a lamp or ceiling light. If you just want to get a general look at an x-ray (perhaps to make sure it's the right one), then all you need is some basic background lighting to reveal the contrast. If you want to see something more detailed about the film, you will need more than just a desk lamp.
• Place the radiograph against a brightly lit window. You can also tape the film in place if it will be needed for some time, such as in the operating room (OR) or when teaching. This works in a way similar to a light box by back-lighting the radiograph so that you can see the contrast.

A view box can quickly (3 hours) and inexpensively (~$63 US) be made from locally available materials, as we did in Kintampo Municipal (District) Hospital in rural Ghana. Our view box is a wooden case containing fluorescent bulbs with a translucent plastic viewing screen. The bulbs are the same as those used in the hospital's ceiling lights. The plastic, available locally, slides into grooves cut in the sides of the box, and can easily be lifted out to change the bulbs. Radiographs rest on a lip at the bottom of the box, and are held in place with both the top wooden slat that anchors the plastic sheet and two wires strung across the front of the box to eye bolts in the sides. The activation switch on the electrical socket is used to turn the light box on and off. Our light box design accommodates two full-size radiographs simultaneously. The light box can be set on a desk or shelf or, as at our hospital, mounted on the wall using standard brackets.2

Makeshift X-Ray Markers

Film Markers

Which is the right side? Normally, films are labeled with either "right" or "left" markers. (On chest and abdominal films, except with situs inversus, it should be obvious.) These metallic markers are small and easily lost. Bend a paper clip into an "L" (easier) or "R" (if you're talented) and tape it on the film as you would with a standard marker.

Foreign-Body Markers

Makeshift markers for foreign-body localization or for entrance/exit wounds in penetrating trauma can be fashioned from BBs (metallic pellets for air rifles), lead markers for radiographs (especially the "O"), vitamin E capsules (for MRIs and CT scans, since they are visible but don't cause scatter), hypodermic needles, electrocardiogram (ECG) or electroencephalogram (EEG) leads, or paperclips.

Paperclips are often most effective as markers if they are "unwrapped," so that only a single wire points to the wound. With plain radiographs, at least two views should be obtained to better localize any foreign body. When using foreign-body markers for a CT scan, unbending them also minimizes scatter at the end of the marker nearest the wound.

One variation on the paperclip foreign-body marker has a "forward arrow" (Fig. 18-3) pointing to penetrating wounds that enter anterior to the anterior axillary line (the front of the body) and a "backward arrow" pointing to those that enter posterior to that line (back of the body). This helps with localizing the penetrating foreign body's (usually a bullet) trajectory.3 Of course, everyone has to know what the different markers mean.

Estimating the Size of a Pneumothorax

The treatment of pneumothoraces depends on their size. Rather than just inserting a chest tube (and using many resources), patients without dyspnea who are <50 years old with a first-time unilateral spontaneous pneumothorax that is "small" can be managed with observation.4

To avoid using any of the complex and often inaccurate formulas and nomograms to calculate pneumothorax size, the British Thoracic Society (BTS) suggests the use of a simple method that works well in clinical practice. They recommend that for a spontaneous pneumothorax, a "small" collapse is when the average interparietal distance (AID) is <2 cm. The AID is an average of the distance between the parietal and visceral pleura at three points: the lung apex, and one-third and three-fourths of the way down the lung. Other recommendations state that the distance between the apex of the chest to the cupula of the lung should be <3 cm to be considered "small."5

Contrast Esophagrams

If necessary, use barium for these studies, since aspirating small amounts of barium causes no problems. Keep the patient sitting upright to reduce the aspiration risk. To reduce the amount of contrast used, patients can swallow a barium-soaked cotton ball rather than the liquid. However, if a foreign body must be extracted after contrast has been used, the procedure can be more difficult. These studies can be done with a portable x-ray machine.

Use water-soluble contrast (e.g., Gastrografin) first if perforation is suspected, since it causes less mediastinal inflammation if extravasated. (Any iodine-containing contrast diluted with water can also be used.) If aspirated, it causes a severe chemical pneumonitis. Do not use it in cases of complete esophageal obstruction. To test for a perforation, have the patient swallow progressively larger amounts of contrast, up to about 50 mL. If that is negative, repeat the procedure with half-strength and then full-strength barium. If fluoroscopy is available, use it. It is easy to miss a perforation using portable radiographs, since you can take only one film with each swallow.

Gas Contrast

Air and carbon dioxide are effective, inexpensive, and readily available contrast agents for the stomach or colon. Inject air directly into these areas using a nasogastric (NG) or enema tube. Children's effervescent tablets can also produce gas if swallowed. Air injected through an NG tube usually provides sufficient contrast to make the diagnosis of a tracheoesophageal fistula in infants. It avoids introducing barium with the real and dangerous risk of aspiration.6

Computed Tomography Contrast

The typical contrast material used for abdominal CT studies is expensive and is not well tolerated by many patients. Whole milk (4%), which is much less expensive, works well as a substitute contrast agent for abdominal CT studies. It seems to work better than 2% milk, water, or no oral contrast agent. Whole milk functions as well as barium suspension for gastrointestinal distention, mural visualization, and bowel loop and pancreas-duodenum discrimination.7 In addition, patients are much more willing to drink the milk and they have fewer subsequent gastrointestinal effects.8

Magnetic Resonance Imaging Contrast

Several positive oral contrast agents for MRI can be improvised. These include pediatric formula and homemade oil emulsions.9 If you have MRI, however, you probably don't need to improvise.

Poor-Man's CT/Tomogram

When CT scanning is not available, plain radiographs can provide a "poor-man's CT scan" of complex structures using stereoscopic imaging. Used until the mid-1980s in the United States, the technique clarifies difficult-to-read films and can localize lesions within a space (such as bullets or cavitary lesions in a chest or skull). It was commonly used for facial bones (such as Water's views) and P-A chest radiographs. It can also be used for complex fractures.

Taking Stereoscopic Films

Stereoscopic films are taken by keeping the part of the body (head, chest, and limb) being filmed still while first taking one film 5 degrees lateral from midline and then another film 5 degrees lateral from midline in the opposite direction (Fig. 18-4). Alternatively, for each film, move the x-ray head to either side of midline, 10% of the distance between the x-ray head and the x-ray plate. The x-ray heads must be kept in the same horizontal plane. Be certain that the patient does not change position while you are changing x-ray plates. Note that some modern x-ray heads cannot be adjusted to shoot films at these angles, although it can be done with all portable machines.

The tube motion must be in the direction of the grid lines if a grid is used to reduce x-ray scatter. (X-ray technicians will understand this.) The grid is usually along the long axis of the table, and built into the x-ray table's Bucky cassette holder. It is also built into wall units, usually with a vertical orientation. The cassette may be placed against the patient (without a grid), although there will be more scatter and lower contrast than with a grid.

If only digital radiography is available, use the same technique to take the films and put them up side by side using the "compare" feature that comes with most digital radiographic readers. The films may need to be rotated to make them line up correctly.

Viewing the Images

Reading stereoscopic radiographs requires either a stereoscopic viewer (generally rare in austere medical situations) or a little practice in crossing one's eyes to form a 3-D image between the two slightly different films. A way to practice this eye-crossing technique is to use the old postcard-type images from a stereopticon or the images from Fig. 18-5. Just slightly cross your eyes until the two images merge in the middle, giving a 3-D picture. This is also how it is done with radiographs. Some people find it easier to merge specific points, such as the black dots below the figures, and then look at the image.

For those who can't cross their eyes to see the stereoscopic image, Dr. E.B. Morton devised a simple stereoscopic viewer using cardboard11:

The simplest stereoscope for X-ray negatives or prints may be improvised in a few minutes. Take a piece of cardboard about 6 in. by 8 in., and cut a rectangular opening in the middle, say 2 in. by 1½ in. The two plates or prints are set upright side by side in a good light and from four to six feet from the observer. The card is held at arm's length, more or less, until the observer's right eye sees only the left hand plate, the left eye being closed, while the left eye sees only the right hand plate when the right eye is closed. Now open both eyes, concentrating attention on the edges of the opening in the card; in a few seconds or less the two images will coalesce, giving a perfect stereoscopic effect. At first it may be a little difficult to secure this, and there may be some ocular fatigue from the use of the muscles in an unaccustomed way, but this very soon disappears, and it is worth while learning how to use a device that can be made in a moment from a piece of dark paper if nothing better is at hand.

To make a similar viewer, enlarge the template in Fig. 18-6 to fit a letter-sized sheet of paper and cut it as indicated. The sides fold up so that it ends up looking like a trough with a hole at one end (marked with an eye) through which you view the images (Fig. 18-7). Use it in the same manner as described by Dr. Morton.

Ultrasound has become the standard imaging modality in many austere situations. It has multiple clinical applications and can easily be operated by the clinician. In addition, its low cost (in comparison to other imaging hardware) and portability are ideal for remote areas. While clinicians now perform a wide variety of ultrasound exams (the E-FAST and gallbladder being the most common), only the less common, but easily performed exams to diagnose fractures and neonatal intracranial bleeding, are described here. Eye exams are discussed in Chapter 27, Ophthalmology.

Ultrasound Gels

In austere situations, "disposable" often means unavailable. That is frequently the case with ultrasound gel. Substitutes include ECG jelly, liquid soap, any water-soluble gel (e.g., K-Y Jelly), and vegetable oil. All provide images comparable to those produced using commercial gels. The problem with vegetable oil, however, is that it is not water-soluble and it stains everything it touches with oil marks. While ordinary soap or water can be used as ultrasound gel, do not use petroleum-based materials, such as Vaseline, since they reportedly damage ultrasound heads.

Probe Protectors

A nonsterile very thin plastic bag, large condom, or rubber glove can be used to protect the ultrasound head when it is being used in the vagina or mouth. Put contact gel into the bag or glove before inserting the probe. Then put additional gel on the outside of the plastic for a good seal. When a sterile probe cover is needed to help guide procedures done under aseptic conditions (e.g., paracentesis, central line placement, and bladder aspiration), use sterile surgical gloves as a probe cover.

Neonatal Ultrasound of the Head

Use cranial ultrasound in infants to check for bleeding. Cranial ultrasonography can easily identify a subependymal hemorrhage or intraventricular blood. It can also be used to identify posthemorrhagic ventricular dilation reasonably well and midline shifts. Evaluation of arterial flow (especially in the neck) and intraparenchymal lesions is operator dependant.

Use a 7.5 MHz probe for premature infants <32 weeks gestation or <1500 g, and a 5.0 to 3.0 MHz probe for older infants with an open fontanelle. With enough gel on the head and probe and with the child restrained, place the probe over and perpendicular to the anterior fontanelle in the coronal plane (across the head) and slowly angle it forward and backward to see the entire brain. The structures, especially those that are blood-filled, should be easy to see. Repeat the process with the probe oriented in the sagittal plane (front to back) and slowly angle it from side to side to see the lateral ventricles and temporal lobe.

Orthopedic Ultrasound

Although bone is a natural obstacle to high-frequency sound transmission, the large difference in acoustic impedance between soft tissue and bone results in a strong acoustic interface. This leads to an almost total reflection of sound energy from the bone, providing an excellent way to examine patients for fractures.13

Selecting the correct patients for examination is the key to using ultrasound for fracture diagnosis (Fig. 18-8). In patients exhibiting signs and symptoms of a fracture, clinicians with minimal training can diagnose many fractures using ultrasound, even those that cannot be seen on radiographs. In patients with a medium-to-low probability of fracture, they are able to successfully rule out the presence of long-bone fractures.14

The ultrasound exam for fracture, which generally takes less than 5 minutes to complete, is usually performed with a high-frequency linear probe (10 to 5 MHz). Physicians can become proficient in administering the exam with only an hour-long standardized formal training session and a practice session on a live normal model.14 Although, demonstrating on a child with a femur fracture, I taught rural Zambian nurses to successfully recognize fractures with ultrasound in 5 minutes. Some inexperienced examiners use pictorial reference cards to locate both ultrasound equipment controls and where to place the probe for various examinations.15

Method

The most common exam is of a long bone. Especially for those not completely familiar with the technique, a useful way to begin is to examine the unaffected extremity and to adjust the depth and maximize visualization of the cortical interface during this part of the exam. The cortical interface appears as an unbroken, strongly echoic line. Using sufficient gel, place the transducer transversely (across) the extremity just proximal to the patella or elbow. Identify the femur or humerus and rotate the transducer 90 degrees so that it lies along the long axis of the bone. Slide it up the extremity (Fig. 18-9). Either the smooth shaft or an obvious discontinuity will be seen. Approaching the femoral neck, angle and rotate the transducer slightly and continue scanning to the midpoint of the inguinal ligament to visualize the femoral neck, head, and pelvic acetabulum. Near the shoulder, scan just distal to the acromial process of the scapula to visualize the humeral head.14,16 If significant bleeding around the fracture has occurred, there may be an overlying hematoma that appears acutely as a hyperechoic area; the hematoma appears hypoechoic in the subacute stage.13