In general, radiologic imaging does not play a major role in therapy of the uncomplicated wound. However, wounds that fail to heal as expected can be further investigated with imaging to identify negative contributory factors that can then be ameliorated. Compromise of vascular inflow and efflux and deep infection may be factors in impaired wound healing, and occult foreign bodies present a nidus for continued inflammatory or infectious complication. Many radiologic examinations are available to augment clinical diagnosis and can be performed either alone or in combination. All imaging modalities have inherent advantages and disadvantages, and the optimal choice of examination is guided by patient attributes and clinical context.
This chapter is divided into technical and clinical sections, first providing a basis for understanding radiologic studies with a description of common contrast agents and precautions. Clinical examples of vascular and soft tissue imaging pertinent to wound care follow, depicting common pathologic conditions with normal comparisons. Varied anatomy is depicted with an emphasis on the lower extremity, and suggested imaging algorithms are presented.
Physical Basis of Modalities
The basic premise for conventional radiographs (x-rays) and computed tomography involves the passage of an x-ray beam through the patient and generation of an image from the radiation that reaches a receptor. The receptor may be as simple as a single sheet of film or as complicated as the data acquisition system of a multidetector computed tomography system, and the amount of radiation passing through the patient to make the image is determined by the density of the anatomic patient structures it traverses. The x-ray beam is a form of ionizing radiation, and as such is a potential carcinogen that should be used wisely for diagnostic imaging.
Catheter arteriography is performed under direct visualization with fluoroscopy, a specialized type of radiographic machine that allows continuous, or "real-time", x-ray visualization. Patients lie recumbent on an x-ray table with a mobile x-ray tube and detector on either side. A needle puncture is made into an artery, usually in the groin, through which a catheter is placed for injection of contrast material. In complicated cases, the x-ray tube may be turned on many times in short bursts, and radiation exposure is on the order of minutes, rather than seconds.
Ultrasound is similar to sonar, and employs a pulsed, focused, high-frequency sound beam delivered and received by an ultrasound transducer. The beam is variably absorbed, deflected, and transmitted by different tissue types, and the amplitude, or strength, of the reflected ultrasound energy returning to the transducer is processed to make a gray-scale ultrasound image. In the context of vascular ultrasound, the direction and speed of flowing blood can be determined by means of the Doppler effect. Sound energy returning from moving objects ...