PEM performs well against breast MRI, whole-body PET

Jun 5, 2007

WASHINGTON - Positron emission mammography (PEM) was comparable to breast MRI and outdueled whole-body positron emission tomography (PET) in a pilot study to determine which modality was most helpful in preoperative surgical planning.

The results were presented on Tuesday at the 2007 SNM meeting by Dr. Kathy Schilling, medical director of breast imaging and intervention at Boca Raton Community Hospital in Florida.

Schilling is involved in a multicenter trial sponsored by PET developer Naviscan PET Systems of San Diego to investigate PEM and breast MRI in breast cancer preoperative surgical staging. The information gathered for the study was acquired prior to her involvement in the Naviscan project.

While mammography has been a reliable screening tool in the past, the report maintains that even when paired with ultrasound, mammography tends to underestimate the extent of breast disease. "Whole-body PET has been known to identify many malignancies and, in particular, with regard to breast cancer, is very good at recurrent disease and metastatic disease," Schilling said. "However, it falls significantly short in identifying early breast cancers and has no place in surgical planning."

PEM versus MRI

Breast MRI has proved to have a high sensitivity rate in identify breast cancers, but often lacks conclusive specificity for patients to avoid additional imaging or biopsy prior to definitive surgery.

The high-resolution molecular imaging PEM device uses the same radiotracer as whole-body PET. Unlike whole-body PET, however, with PEM a patient sits upright in a chair during the breast imaging procedure, eliminating the issue of claustrophobia and weight limitations.

A patient sits upright in a chair with the breast positioned between two detectors. All images courtesy of Dr. Kathy Schilling.

The breast is immobilized between the two detectors to reduce respiratory motion and artifacts and improve image quality. The two parallel detectors are in contact with the breast to enhance spatial resolution through their close proximity to the breast. "Also, we are able to mimic mammographic views, which make it easier to co-register our findings with conventional mammography," Schilling said.

The study included a total of 30 women, with an average age of 60 years, ranging from 33 years to 85 years; most were postmenopausal. The women had biopsy-proven breast cancer and were considered candidates for breast conservation. They also were no-diabetic and willing to undergo sequential breast MRI, whole-body PET, and PEM.

The patients first underwent PEM imaging, followed by a whole-body PET exam. The PEM scans had a minimum of four images, with 10 minutes of acquisition time for each. The injection of FDG dose was similar to that of whole-body PET, with a circulation time of 16 minutes.

Breast MRI exams were conducted on a different day. The images were acquired with a seven-channel breast coil, combined with turbo STIR coronal imaging and turbo T2-weighted axial and pre- and postmultiphase dynamic, contrast-enhanced 3D Flash gradient-echo imaging.

There were 26 patients with invasive cancers, which included two invasive lobular cancers, two invasive tubular cancers, and 13 ductal carcinoma in situ (DCIS) cases. The size of the lesions ranged from 8 mm to 44 mm, with a mean index size of 21.6 mm.

PEM's potential

According to the results, whole-body PET detected 12 lesions in the 26 studies completed for a sensitivity rate of 46%, while breast MRI discovered 25 lesions in 27 studies for a sensitivity rate of 96%. PEM detected 26 lesions from 28 studies completed for a sensitivity rate of 93%, but Schilling noted that the lesions missed in two patients were outside of the camera's field-of-view.

Pathology revealed a total of 39 cancers, of which PEM detected 36 lesions (excluding the two lesions out of the field-of-view) for a sensitivity of 92%. Breast MRI detected 35 lesions (one patient did not complete the MRI scan due to claustrophobia) for a sensitivity rate of 90%. Whole-body PET had a sensitivity of 38%, having found 15 lesions. Mammography discovered 28 lesions for a sensitivity of 72%.

With PEM, a lesion can be seen in the mammary fold (left) and in low axillary lymph node (right).

PEM is "the best-tolerated modality by patients," Schilling concluded. "It is as sensitive as MRI in the detection of invasive and noninvasive breast cancer; it can identify pathologic atypia better than breast MRI; and PEM can offer quantitative information, which may assist in the pathological discrimination between benign and malignant lesions."

Schilling also noted that more work needs to be done to confirm these preliminary results.

By Wayne Forrest
AuntMinnie.com staff writer
June 6, 2007

PEM turns in solid results for detecting breast malignancies, November 10, 2005

PET mammography unit shows promise for DCIS, June 22, 2005

PEM development picks up pace, February 7, 2005