Calling it "one-stop shopping" imaging, researchers at NYU's Kaplan Comprehensive Cancer Center are touting perfusion-based MRI as an effective method for distinguishing recurrent brain tumors from radiation necrosis.
With oncologists taking a more aggressive approach to treating tumors with radiation and chemotherapy, finding an efficient, noninvasive means for separating tumors from necrosis is especially crucial, said Dr. Edmond Knopp, an assistant professor of radiology at the New York University Medical Center.
Knopp and colleagues reviewed the records of 35 patients with a history of treated intracranial neoplasm. All had received radiation treatment, including high-dose external beam radiation or radiosurgery.
The patients required follow-up imaging because of the possibility of a recurrent tumor or radiation necrosis. Conventional MR findings were compared to MR measurements of the relative cerebral blood volume (rCBV) of the lesions.
"What we're looking at is the degree of vascularity," Knopp explained. "We are imaging the capillaries. With conventional MR, you're looking at the integrity of the blood-brain barrier, but not the regional vascularity. But what tumors also do is recruit their own blood supply. The perfusion study is looking at the volume and size of the capillary, and if it's increased, the tumor is there."
Using contralateral white matter as the comparison standard, MR perfusion of the lesion was considered hyper-perfusing when rCBV was greater than one, according to the study results. Tumors were confirmed histologically in 30 patients who had an area of hyper-perfusion within the lesion. In the five patients without increased rCBV, the lesion was found to be post-therapy radiation necrosis.
Knopp and his co-authors presented their initial findings at the 1999 annual meeting of the Radiological Society of North America.
In general, nuclear medicine has been the imaging modality used to differentiate recurrent tumors from necrosis. According to the results of a French study from the Service Central de Medecine Nucléaire in Lille, SPECT scans yielded a sensitivity of 73% and a specificity of 95% for the detection of tumor recurrences (Neurochirugie 1999 May; Volume 45, No.2, pp.110-117). MR imaging "is not always reliable in the differential diagnosis between radionecrosis and recurrence," the authors stated.
Another study conducted at the University Hospital Utrecht in the Netherlands compared 201-Tl SPECT to 18F-fluorodeoxyglucose PET, and found the former to be a more sensitive modality for the detection of brain tumor recurrence (Nucl Med Commun 1999 May; Volume 20, No. 5, pp.411-417).
But Knopp pointed out that PET and SPECT are not as readily available at facilities as MR equipment, and more centers are using perfusion-based MRI for imaging stroke patients.
Knopp and his team have also developed a post-processing software package that they are making available to other imaging facilities, he said. The main requirement for running the software is a short-bore, high-field system. A Siemens 1.5-tesla Magnetom Vision is installed at Kaplan.
Knopp said additional studies on a larger patient population are in the works to further track recurrent tumors with perfusion-based MR. The group also will take a look at using MR spectroscopy to match blood volume to perfusion.
Referring physicians are quite pleased with the results of the MR perfusion imaging done at Kaplan, and have made specific requests for it, Knopp said. However, one hurdle is the current lack of reimbursement for perfusion-based MR, he added.
By Shalmali PalAuntMinnie.com staff writer
January 12, 2000
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