High frequency 40-MHz ultrasound - A possible noninvasive method for the assessment of the boundary of basal cell carcinomas

BACKGROUND. Ultrasound imaging systems operating close to 20 MHz in frequency have been used to image skin tumors. Ultrasound imaging at 20 MHz has been used to determine the boundaries of basal cell carcinomas (BCCs). An inherent short-coming of imaging systems operating at these frequencies is their limited resolution. OBJECTIVE. We investigated whether 40-MHz ultrasound imaging could provide higher resolution compared with the lower frequency systems and thus be a superior, noninvasive method of assessing the boundaries of BCCs. METHODS. Nine BCCs from six individuals were examined clinically and ultrasomographically, and then biopsied to confirm diagnosis. The depth of BCCs measured on histological sections was compared with the corresponding value obtained using ultrasound. For this study we required a nonsurgical, nondestructive means of treating BCCs that would allow repeated ultrasound imaging, and therefore topical 5-fluorouracil (5-FU) was chosen. Following 5-FU therapy a biopsy was obtained from the site of the treated BCC after ultrasound imaging had been performed. Clinical, ultrasonic and histopathologic evaluation of each BCC was carried out independently by different individuals. At the end of the study all the BCC sites were treated surgically be electrodesiccation and curettage or completely excised. RESULTS. High resolution ultrasound images of BCCs were obtained with agreement between histology and ultrasound findings in all nine lesions prior to therapy and in eight of nine lesions posttherapy. There was a significant correlation between the depth of BCCs measured histologically and using ultrasound (P = 0.0004, r = 0.92). CONCLUSIONS. This study suggests that 40-MHz ultrasound may provide an estimate of the boundary of a BCC in vivo. High frequency 40-MHz ultrasound imaging may be an adjunct to clinical and histologic evaluation but does not replace the need to obtain tissue for microscopic examination.