CE ultrasound broadens scope of clinical utility

Canadian and U.S. radiologists face different regulatory restrictions for the use of ultrasound contrast agents. However, both sides are coming up with similar evidence about their positive effect on clinical practice. CE sonography shows promise for diagnosis and management of gastrointestinal and genitourinary malignancies, particularly in the liver and prostate, according to studies presented at the 2006 RSNA meeting.

Investigators led by Dr. Stephanie R. Wilson, chief of ultrasound at the University of Toronto's General Hospital, retrospectively reviewed data from 1088 patients collected between July 2003 and December 2005. They found the use of CE sonography in this setting bolstered patient management by providing fast, accurate detection of liver masses and resolving inconclusive findings by other imaging modalities. The team confirmed that the number of referrals for this type of exam increased progressively during the two-year study period. They also noted CE sonography helped reduce referrals for more expensive imaging.

"Contrast-enhanced sonography has had a very positive impact at our institution," said medical student and team investigator Bina Lanka, who presented the study.

In a separate study, Dr. Yuko Kono, a radiologist at the University of California, San Diego, recorded results arising from off-label use of ultrasound contrast agents between 2000 and 2006. The research team found that although few patients underwent CE sonography studies during this period, its use added critically valuable information in 75% of the cases in which it was used, without increasing risk. Applications included detection and characterization of liver tumors; vascular patency in patients with transjugular intrahepatic porto-systemic shunts (TIPS); and renal, splenic, and other abdominal abnormalities. CE sonography replaced inconclusive contrast CT or MR studies in most cases, Kono said.

"Ultrasound contrast is useful in many applications and helps clinical practice. We need approval in the U.S.," Kono said.

Conservative estimates indicate that more than 230,000 new cases of prostate cancer will be detected this year. Nearly a million biopsies will be performed to arrive at that number. Several studies have shown that sextant biopsy, the standard of care for a decade, misses more than 30% of cancers. With many physicians currently taking 10 cores or more, biopsy's cost-effectiveness comes into question.

"That's a lot of biopsies. There's also a potential risk of morbidity," said principal investigator Dr. Ethan J. Halpern, a professor of radiology and urology at Thomas Jefferson University.

Halpern and colleagues compared the performance of two CE ultrasound scanning techniques, microflow imaging (CE-MFI) and continuous harmonic imaging (CE-CHI), on 11 patients referred for biopsy.

The investigators took up to five targeted biopsy cores from areas of abnormal vascular enhancement or morphology signaled by either CE-ultrasound technique. They also performed a systematic 10-core biopsy protocol. They found that CE-MFI of the prostate provided a better, clearer depiction of the prostate's vascular flow pattern compared with CE-CHI. They also found that CE-MFI helped increase biopsy's detection rate via targeted biopsy.

CE-MFI provided targeted biopsy sites showing hypervascularity and abnormal morphology that were not visible with CE-CHI. These sites accounted for nine of 16 positive core biopsy specimens. Eighty-two percent of cores detected in this fashion were positive in the three patients diagnosed with cancer. One patient with prostate cancer was identified only by targeted biopsy with CE-MFI.

Contrast-enhanced microflow imaging provides a clear depiction of vascular patterns in the prostate, especially those that are cancer related. Biopsies targeted with microflow imaging are twice as likely to be positive compared with systematic cores, Halpern said.

"What we are hoping to work toward is a system where you can do just targeted biopsies and, thereby, reduce the total number of cores taken and improve patient morbidity," he said.