HiSS imaging challenges contrast MRI for tumor characterization

A new approach that detects breast cancer vasculature is making an appearance at the 2010 RSNA meeting. The method, called high spectral and spatial resolution, or HiSS, uses water to detect tumor blood vessels without contrast. 

Two papers on the topic have been presented. The first identified blood vessels and distinguished between malignant and benign breast lesions. The second compared precontrast HiSS MRI with conventional contrast-enhanced MRI for classifying malignant and benign breast lesions.

HiSS is a type of spectroscopic imaging that does not visualize metabolites. Instead it separates the water and fat signals, allowing elimination of the fat signal in postprocessing.

In the first study Abbie Wood, a physics graduate student at the University of Chicago, and colleagues determined anatomic and physiologic features that cause local magnetic susceptibility gradients to produce partially resolved off-peak components in the water resonance. The off-peak components include paramagnetic deoxyhemoglobin, calcifications, and hemosiderin. Cancers tend to have elevated levels of deoxyhemoglobin, and this effect is detectable in vivo. Wood and colleagues evaluated off-peak components of the water resonance as a marker for malignant breast lesions.

In 24 patients, the investigators found 16 invasive cancers and eight benign enhancing breast lesions. Patients were imaged with MRI while HiSS data were acquired using an echoplanar spectroscopic imaging (EPSI) sequence with 1 x 1 x 2-mm3 voxels and a spectral resolution of 2.5 Hz. Dynamic-contrast–enhanced MR images were acquired with temporal resolution of one minute. Images were generated from the frequency difference between the peak of the water resonance and the largest off-peak non-Lorentzian spectral component.

The researchers found frequencies of off-peak components were significantly larger in malignant lesions than in benign lesions. Frequencies of off-peak components were similar in benign lesions and normal parenchyma. They also found contrast media washout kinetics were significantly different in malignant and benign lesions. Contrast washout was detected in more of the malignant lesion pixels than in the benign lesion pixels.

“We found a noninvasive method of diagnosing breast lesions, which provides new functional information that could improve diagnostic accuracy when paired with dynamic-contrast–enhanced MR results,” Wood said.

Wood was awarded the trainee research prize for her abstract.

The second paper, presented by Milica Medved, Ph.D., an assistant professor at the University of Chicago, found precontrast HiSS images performed as well as conventional postcontrast images in differentiating benign and malignant lesions.

“This is of high significance for the large number of patients for whom contrast agent administration is contraindicated due to poor kidney function or allergic reactions,” Medved said. “In addition, precontrast HiSS imaging could be used for improved assessment of lesion morphology without blurring artifacts due to contrast agent administration.”