Diagnostic Imaging and Interventional Radiology

• Author: Samuel D. Hodge, Jr./Jack E. Hubbard
• Profession: Skilled litigator, is chair of the department of legal studies at Temple University/Professor of Neurology at the University of Minnesota
• Pages: 67-138

Diagnostic Imaging

and Interventional

Radiology

Millions of Americans

every year depend

upon medical imaging

exams to diagnose

disease and detect

injury. . . .

Charles W.

Pickering (b. 1937)

2

“Ladies and gentlemen of the jury, you know the expression ‘a picture is worth a thousand

words.’ Well, I have an image that proves my client suffered significant spinal trauma. I

have the equivalent of an anatomical drawing of my client’s lumbar spine and it shows a

large herniated disk at L5/S1. This image was created by an MRI and provides unques-

tionable proof of my client’s abnormality. In fact, I will show you the image during trial

and you will see for yourself the plaintiff’s painful herniation.”1

The development of and advancements in radiological diagnostic imaging have been

a major contribution to the ability of physicians to diagnose and treat most medical

conditions. Further, computers have had a profound impact on the ability of imaging

modalities to diagnosis spinal abnormalities. For instance, a computerized axial tomog-

raphy (CT) scan is based upon an x-ray machine that is linked to a computer to create a

cross-sectional image of the spine that allows the visualization of internal anatomy and

boney structures. Magnetic resonance imaging utilizes a computer to create an image so

exquisite in detail that it resembles an artist’s rendition of the body.

These tests form that part of medicine known as diagnostic radiology and are fre-

quently used tools to diagnose or confirm problems with the spine. These diagnostic pro-

cedures, however, are not well understood by the legal community even though medical

imaging finds its way into the courtroom on a regular basis.

Also, those who believe that these diagnostic procedures are infallible objective evi-

dence of an injury are mistaken in those beliefs. These tests have limitations, including

false positives and overreading by physicians. While the images generated by the tests are

objective, the interpretation of the results as formally recorded in the radiology report is

dependent upon the subjective opinion made by the radiologist.

In addition to diagnostic imaging, the specialty of radiology is branching out to actual

treatment of various conditions including radiation for healing, such as in cancer treat-

ment. This application is termed therapeutic radiation. Radiologists also perform inter-

ventional procedures such as injections and stent placement to treat patients.

This chapter discusses the more common diagnostic imaging techniques used by phy-

sicians and presents some of the limitations and risks of these procedures. This discus-

sion will be broader than just those imaging modalities that deal with the spine because

they are so important in the modern practice of medicine. Interventional radiology and

nuclear medicine will also be explored because of the developing role of radiologists in

the treatment of disease.

68 ◆ CHAPTER 2

Diagnostic Imaging

Diagnostic imaging refers to the technologies that physicians utilize to peer inside the body

for clues about a medical problem. A variety of imaging modalities can create pictures of

internal body structures and activities. The specific technology ordered by treating phy-

sicians is determined by the medical problem being evaluated and the part of the body

being examined.2

Ever since Hippocrates painted a patient’s body with wet clay and discovered that

the mud dried quicker on the diseased area made warm by infection or inflammation,

physicians have sought ways to evaluate the condition of a bone, soft tissue, or organ in

a noninvasive manner. Historically, examination of body regions was accomplished by

palpating the structure in question. The inherent limitations in this approach are that the

significance of an abnormality is subject to the clinician’s interpretation3 and that quite

simply, many body parts, such as the living brain, cannot be examined in this manner.

The expansion and reliance on medical imaging during the past few decades has pro-

vided important and life-saving benefits to patients. However, overutilization of these

tests can be detrimental because they may expose patients to unnecessary radiation.4

History

The face of medicine changed in 1895 when Wilhelm Roentgen, a German physicist,

accidently discovered the x-ray, thereby creating the first test for identifying anatomi-

cal abnormalities within the body. At the time, Roentgen was examining the phenomena

accompanying the passage of an electric current through a gas of extremely low pressure.

He learned that if the discharge tube is encased in a sealed, thick black carton, and if the

room is darkened, a paper plate covered on one side with barium platinocyanide placed

in the path of the ray beam becomes fluorescent. Subsequent experiments revealed that

materials of different densities showed a variety of transparencies on a photographic plate.5

For the first 50 years, the technique was limited to creating an image by focusing

x-ray beams through the body part being studied and directly onto a piece of film inside

a special cassette. In the earliest days, an x-ray could require 11 minutes of radiation to

create an image.6

Following the development of sonar as a military tool during World War II, high-

frequency sound waves, termed ultrasonography, were used to study the body. A drawback

at that time was that the patient had to be emerged in water for the test to work.7 Diag-

nostic medicine underwent another revolution with the introduction of the computer,

which allowed more complex imaging such as the bone scan, and improved ultrasound

imaging, which allowed evaluation of internal body functioning. As computer technology

advanced, imaging modalities have kept pace with the creation of the CT (computerized

tomography) scan and MRI (magnetic resonance imaging). In fact, the MRI requires no

radiation to produce images. Instead, the technology utilizes a powerful magnet and radio

waves to create images that are so detailed they look like an artist has drawn the inter-

nal structures of the patient. Needless to say, these developments have brought a fresh

approach to forensic documentation.

Diagnostic Radiology

Diagnostic radiology involves the use of radiation and other methods to image a structure

within the body. Procedures range from plain film x-ray to more sophisticated tech-

niques, which create three-dimensional pictures. Radiocontrast agents, loosely referred

to as a “dye,” help to outline and visualize the soft-tissue structures, such as blood vessels,

which are not normally seen on plain film studies.

A radiologist is a physician who specializes in diagnosing and treating diseases and inju-

ries through the use of medical imaging modalities. These specialists complete medical

school as well as a radiology residency of at least four years in areas such as radiation

safety, radiation effects on the body, and performance and interpretation of radiological

and medical imaging examinations. These imaging specialists may also pursue a fellowship

in a subspecialty, such as breast imaging, cardiovascular radiology, or nuclear medicine.8

DIAGNOST IC IMAGI NG AND IN TERVEN TIONAL R A DIOLOGY ◆69

Radiographic Procedures

Plain Film X-Rays

Most people have undergone an x-ray examination. The test accounts for more than 75

percent of all imaging procedures. A plain film imaging system consists of an x-ray source,

a beam-limitation device, and film. Figure 2-1. The x-ray source is a high-energy glass vac-

uum diode tube. When energized, electrons shoot through the vacuum from the cathode

to the anode. The beam-limitation device allows the technician to limit radiation exposure

to the area being studied, thereby protecting the patient. The film is sensitive to both light

and x-ray, so it must be enclosed in a light-proof holder called a cassette.9 Increasingly,

digitized systems are being used instead of film to store the information electronically.

Where the beam of electrons passes through the body, the developed film plate will

appear lighter, forming an image, depending upon the density of the targeted body part

through which the beam has passed. Solid bone, which is dense because it contains cal-

cium phosphate, absorbs radiation, causing that part of the film to be less exposed or

whiter, much like a shadow that is cast when sunlight strikes an object. X-rays, therefore,

provide accurate evidence of bone pathology, such as a fracture (Figure 2-2a) or bone

cancer. Additionally, degenerative changes, such as bone spurs and loss of intervertebral

disk height, are visible. On the other hand, soft tissues, such as the brain, muscles, disks,

and organs such as those in the pelvis and abdomen (Figure 2-2b), are much less dense,

as they have a high water content with little or no calcium. Because of their decreased

density, these tissues offer little resistance to x-ray beams and are not seen on the result-

ing x-ray image. The resulting lower tissue density causes the corresponding part of the

developed film to darken providing little detail for diagnostic interpretation. Therefore,

plain x-rays are not useful for the evaluation of soft-tissue pathology such as disk hernia-

tions and nerve root impingement. Although x-rays can provide graphic illustrations of

anatomical abnormalities, the images must be taken in a variety of views and angles to

not miss an elusive problem. A relative contraindication for x-rays is pregnancy, unless

the abdomen is shielded with a lead apron. Another possible limitation is an allergic reac-

tion to the radiographic contrast dye, if used. Because of the iodine content, many people

FIGURE 2-1.

Plain x-ray physics.

X-rays generated in an x-ray tube

are directed toward the patient.

The resulting image depends

upon the density of the body part

and is visualized on x-ray film or

electronic detector. Denser struc-

tures such as bone block the x-ray

beam, with the resulting image

appearing white on the x-ray film.

Conversely, less dense structures

such as the air-filled lungs do not

block the x-ray beam and appear

darker on the film. Some systems

reverse the process such that more

dense structures appear darker.