Collateral Damage: The Lowdown on Diagnostic Imaging

It's been a very slow weekend in terms of injuries, but that doesn't mean we have to slow down here in the Collateral Damage corner of Baseball Prospectus. There are many different diagnostic tests used in sports medicine, and you hear them mentioned all the time in injury reports. X-rays were negative for a fracture, but the CT scan showed a tiny one. An MRI revealed a possible stress fracture, but then a bone scan was ordered. What's this about using ultrasound in sports medicine clinics? Isn't that what they use during pregnancy? We're going to look at those questions and more in a special installment of Collateral Damage.

X-rays
X-rays are the most common type of diagnostic imaging performed today, in part because they are the most easily available. X-rays don't require a large area, which allows them to be completed inside a room in the doctor's office, unlike other forms of imaging. X-rays are most often used to diagnose gross fractures and malalignment of the bones, such as dislocations, but they can be—and often are—used to diagnose pneumonia, lung cancer, intestinal obstructions, or kidney stones.

Digital X-rays are replacing old-fashioned photographic films because of the significant savings over the lifetime of the machine in larger clinics, as well as the decreased time necessary to process the images. In the process of taking an X-ray, radiation is briefly sent from the X-ray machine through the body part, captured, and then processed into an image. Bones and tumors—which are more dense than other soft tissues—will show up as white on the image because they absorb the radiation. A trained operative also discern the amount of joint space available, which can convey an idea of whether advanced arthritis is present.

Radiation is always a concern with X-rays, but background radiation from outer space and radon gas seeping up through the earth is present everywhere. The amount of radiation in X-rays of the extremities is near zero, the equivalent of standing outside for three hours. If you have an X-ray of the spine, there's more radiation involved, equivalent to standing outside for 6 months. Medical professionals try to limit the number of repeat X-rays because of the risk of additional radiation, but at times the imaging it is necessary.

MRI
Magnetic resonance imaging (MRI) is used in sports medicine to provide more information about the soft tissues than X-rays can. There are various types of MRI, which has several different applications in medicine. MRI does not involve radiation, an advantage that does not go unnoticed among health care professionals. The person undergoing an MRI lies flat on the table—although newer, stand-up models have been developed—while very strong magnets spin around the body part in question. This creates a magnetic field, and radio waves, which are not radioactive, are systematically sent to the body part. The radio waves cause the different tissues to resonate at different rates, allowing the scanner to pick up these separate frequencies.

MRIs takes anywhere from 30 to 90 minutes, but they provide detailed information about assorted soft tissues in the body. A computer measures all of the frequencies and provides an array of pictures at a set distance between each picture. Each structure of the body part will yield a certain shade or color, i.e. ligaments are one shade, fluid is another, muscle is another, bones are another, etc.

The contrast between the separate structures in MRIs allows radiologists to identify different injuries. Tears of ligaments or tendons can be detected, as well as injuries to the meniscus. Contusions are easily seen on MRI, regardless of whether they’re located in bone or soft tissue. Herniated disks and other cartilage injuries throughout the body can also be revealed clearly.

In some cases, orthopedic injuries aren't easily seen on regular MRI. In these cases, a dye is used to give us more detail and allow a more accurate diagnosis. This dye, often gadolinium, can be injected into the joint (direct) or via the bloodstream (indirect). Several injuries could require dye to provide a more accurate diagnosis, but the ones that invite its use most often are UCL injuries and labrum injuries in the shoulder and hip.

CT scan
A computed tomography (CT) scan, or CAT scan, as it's commonly called, is another diagnostic imaging technique that uses radiation to provide information about injuries. CT scans use computers and a rotating x-ray tube to generate a very detailed picture of the architecture of the area. Newer CT equipment even allows three-dimensional images to be produced, providing an even more faithful representation.

The main advantage of using CT scans is their ability to detail bone, soft tissue, and blood vessels all at once and in great detail. CT scans can give detail to the 0.2 mm level, providing the granularity needed to diagnosis some injuries. We have seen CT scans revealing small fractures that didn't show up on X-ray or MRI a few times already this season.

Like most things involving an upside, CT scans do involve a downside. The main downside to a CT scan is the amount of radiation, which is much higher than in a regular X-ray. A CT scan on an extremity, such as an ankle, provides about 20 times as much radiation as an X-ray, but it is still extremely safe and equivalent to roughly 10 days of environmental radiation.

If a CT scan is needed for the spine, though, it produces the equivalent of three years of environment radiation. Responsible doctors and CT technicians will consider the patient's exposure to previous CTs and other radiographic images before performing such a scan. If a repeat CT is needed, often it will be focused to a much smaller area, thus decreasing the overall radiation exposure.

Bone Scan
A bone scan is an imaging technique that differs from the other tests in that it doesn't evaluate the architecture of the body part, instead examining the metabolic activity of the area. A radioactive tracer is injected into the bloodstream, which then gets absorbed into the bones. A specialized camera picks up the areas that are very metabolically active—stress fractures or cancers show a very high concentration of the tracer as a dark area, providing a clear contrast with the other areas.

The tracer then dissipates quickly inside the body, usually within a day. The average bone scan is equivalent to approximately one year of environmental radiation, one of the main reasons that bone scans are often performed only once during the diagnostic and treatment process.

Ultrasound
Ultrasound is different from the above tests in that it can be performed dynamically, one of the main reasons that its use among sports medicine professionals is rising. Ultrasound involves sending high-frequency sound waves through a transducer into the body, generating a real-time image on the screen. It acts on the same principle as radar: different tissues will bounce the waves back at different intervals, based on their distance from the source.

One of the biggest advantages of diagnostic ultrasound is its ability to evaluate tissues dynamically, allowing the technician to see their interaction. Rotator cuff tears can be seen and UCL sprains can be evaluated, revealing how loose the ligament is. With the elbow in motion, any scar tissue can be seen and determined to be a source of pain. Tendons can be evaluated for degeneration resulting from chronic inflammation. Ultrasound has a wide range of uses, but one limiting factor is its inability to penetrate outer layers of bone, which MRI or CT is better suited for.

Diagnostic ultrasound has no known side effects in humans, another advantage that cannot be overlooked.

Summary
All of the above tests are used regularly in sports medicine, along with many others. Which one should be used depends on what the medical team is looking for. Plain X-rays can be useful in quickly determining gross fractures or malalignment. MRI is the preferred option to evaluate major joints, intervertebral disks, bones, and soft tissues of the extremities. CT scans are often used to examine structures in greater detail, especially in the setting of acute spinal injuries. Bone scans can reveal how active the bone is, while diagnostic ultrasound can provide real-time dynamic images of soft tissues.

** Information about radiation levels of the different tests and environmental equivalents were found hereand here.

Flesh Wounds: Even though it's a short list, we still had some injuries over the weekend. Martin Prado is suffering from a staph infection in his right calf. He needed a minor procedure to clean out the area, and a trip to the disabled list was deemed necessary… Freddy Sanchez dislocated his right shoulder after a diving catch on Friday and may end up needing surgery… Evan Meek is going to see Dr. Andrews today because of his recurrent shoulder inflammation… Allen Craig is the latest player to go on the disabled list with a knee contusion… Aaron Harang was placed on the disabled list because of a stress reaction in his right foot… Bartolo Colon went on the DL with a strained left hamstring, and Amaury Sanit joins his teammate on the disabled list with right elbow inflammation… Mike Napoli is on the disabled list and continued the recent trend toward oblique injuries… Cole Kimball will be out for at least two more weeks after being placed on the disabled list with right shoulder inflammation… Alberto Callaspo strained a left hamstring but will be considered day-to-day for now… Kerry Wood has developed a blister on his index finger and may require another trip to the disabled list.