Gray Scale Imaging and Doppler Analysis in Cancer Detection
Abstract & Commentary
Synopsis: Gray scale imaging and Doppler analysis of the prostate are relatively insensitive to detect cancer. To detect cancer, multiple bilateral biopsies obtained from the peripheral gland are required.
Source: Halpern EJ, Strup SE. Using gray-scale and color and power Doppler sonography to detect prostatic cancer. AJR Am J Roentgenol 2000;174:623-627.
In this study of 251 men who underwent trans-rectal sextant prostatic biopsies, an attempt was made to evaluate gray scale and color and power Doppler for: 1) the detection of prostate cancer; and 2) to determine the effect of operator experience on the examination. The sonographic examinations and biopsies were performed either by one of four radiologists with prior gray scale and Doppler imaging experience, or by one of four urologists with prior gray scale experience, but without prior Doppler imaging experience. Based on the sonographic gray scale and Doppler appearances, each biopsy site was classified prospectively as either normal or abnormal. Kappa (k) values were used to statistically validate the agreement between the sonographic and pathologic findings, with a k value of -1 indicating absolute disagreement, 0 indicating chance agreement, and +1 indicating absolute agreement.
The results revealed cancer in 211 biopsy specimens obtained from 85 patients (34% of the patient population). The gray scale sensitivity and specificity were 44% and 74%, respectively; Doppler imaging (color and power) had a sensitivity and specificity of 27% and 77%, respectively. Only 35 of the 211 lesions (17%) were considered abnormal by both imaging modalities, and 96 lesions (45%) were completely overlooked by both techniques.
When gray scale was used to detect prostate cancer, both radiologists and urologists had similar sensitivity and specificity (k = 0.13 vs 0.12, respectively). With respect to power Doppler, radiologists performed significantly better than urologists (k = 0.09 vs -0.03, respectively; P < 0.002).
Comment by Faye C. Laing, MD
The results of this study reaffirm that despite using state-of-the-art gray scale equipment and integrating the findings with color and power Doppler, ultrasound’s sensitivity remains disappointing with respect to its ability to detect focal changes associated with prostate cancer. Other disappointing findings reported by Halpern and Strup were that even with a relatively large tumor burden (reflected as a PSA level of > 10 ng/mL) or a biologically more neoplastic tumor (reflected as a Gleason score of > 7), the sonographic detection rate remained low. The fact that radiologists performed better than urologists when power Doppler was used cannot argue for radiologists doing this examination, because power Doppler was, in and of itself, insufficiently sensitive for detecting cancer.
How then should men be triaged and evaluated for prostate cancer? PSA screening and digital rectal examination remain at the forefront for detecting this disease, which in the United States results in approximately 37,000 deaths each year. If the PSA determination is greater than 4 ng/mL and/or a suspicious digital finding is palpated, transrectal biopsy is warranted. This should be done by an experienced physician, and in cases that reveal a sonographically normal appearing prostate, at least six transrectal samples from the outer gland should be sampled. These are usually obtained bilaterally, from the base, mid-gland, and apical levels. If a gray scale abnormality is detected, at least one of the biopsies should include this site. One could also argue that color or power Doppler should be used routinely, because if a focal area of increased blood flow is detected, this too should be used to target the biopsy sampling site.
Despite these best efforts, however, it is important to realize that when state-of-the-art equipment is used by experienced examiners and multiple prostatic biopsies are obtained, only one in three men will be shown to have cancer.
With respect to detecting prostate cancer by transrectal sonographic examination, the results of this study suggest:
a. the combined results of gray scale and Doppler imaging detect more than 75% of cases.
b. the combined results of gray scale and Doppler imaging detect 50-75% of cases.
c. the combined results of gray scale and Doppler imaging detect 25-50% of cases.
d. the combined results of gray scale and Doppler imaging detect fewer than 25% of cases.
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