NEW YORK--Transrectal ultrasound is a valuable tool in the diagnosis of prostate cancer, but much can be done to optimize the procedure. W. Holt Sanders, MD, assistant professor of urology, Emory University School of Medicine, says that the basic principle is to "make sure the area of interest is within the focal range."
NEW YORK--Transrectal ultrasound is a valuable tool in the diagnosisof prostate cancer, but much can be done to optimize the procedure.W. Holt Sanders, MD, assistant professor of urology, Emory UniversitySchool of Medicine, says that the basic principle is to "makesure the area of interest is within the focal range."
Speaking at a Lenox Hill Hospital conference on prostate cancer,Dr. Sanders explained that ultrasound penetration and resolutionquality are inversely
proportionate. High-frequency sound waves penetrate poorly butoffer good resolution; low-frequency waves penetrate farther butwith poor resolution. "The frequency can therefore be increasedto improve visualization of the posterior part of the gland, anddecreased if necessary to better view the anterior zones of theprostate," he said.
Dr. Sanders pointed out that the majority of cancers (70%) originatein the peripheral zone of the gland, 25% in the transition zone,and 5% in the central zone. Tumors do not originate in the fibromuscularzone. With an adjustable machine, the frequency can be altered,depending on the area being viewed. On machines that are not adjustable,a mid-range of 7 mHz is usually used.
The ultrasound automatically enhances the image by time-gain compensation,he said. By amplifying more distant signals, visualization ofmore distant structures is improved.
Dr. Sanders also stressed the importance of knowing the focalrange (the range of optimal resolution) of the ultrasound machine.With that knowledge, the operator can move the transducer so thatthe area of interest is within the focal range.
He offered a tip for correcting reverberation, a common and annoyingaberration in the ultrasound image that occurs when sound waveshit an interface at a right angle: Avoid a right angle by movingthe transducer off the midline, tilting it instead.
He also cautioned that the height of the prostate should be measuredin the longitudinal view; this strategy assures that the heightmeasurement is perpendicular to the length measurement.
Normal and abnormal structures show up characteristically, dependingon how sound bounces off them, he said. Hyperechoic structuresappear lighter than hypoechoic structures, and anechoic structuresappear as black areas.
These characteristics makes it possible to detect on ultrasoundsuch benign conditions as BPH, calcifications, obstructions inthe seminal vesicle, cysts (which are anechoic), granulomatousprostatitis (seen as diffuse hypoechoic areas), and ureteroceles.