Pilot study of Velocity-selective Arterial Spine label MRI (VSAL-MRI) derived relative cerebral blood flow to distinguish imaging changes after radiosurgery for brain metastasis from progressive tumor.

Purpose: VSASL-MRI is an investigational method to measure tissue perfusion. Velocity selective arterial spin labeling (VSASL) uses water activated by a magnetic pulse as an endogenous tracer to measure tissue perfusion using velocity-sensitive MR labeling applied non-selectively in space. Advantages include no IV contrast, limited susceptibility artifact, and absence of confounding leakage of gadolinium contrast into tissues. The Objective is to test the hypothesis that VSASL-MRI has the potential to distinguish progressive tumor from imaging changes consequent to radiosurgery which appear similar on standard contrast enhanced MRI (cMRI).

Methodology: Patients had one or more brain metastasis from a solid tumor with progression on cMRI. VSASL imaging was obtained and patients followed for clinical outcome. Images of the index progressive lesion were categorized (in comparison with normal brain) as hyperperfused, potentially representing vascularized progressive tumor or hypoperfused, potentially indicating imaging changes consequent to radiosurgery.

Results: 10 patients with solid tumor and a radiosurgery treated brain metastasis progressing on cMRI were enrolled and VSASL-MRI was performed. 7/10 patients had hypoperfusion of the index lesion. The time interval from radiosurgery for these lesions and the outcome on clinical follow-up was: one patient (57 months after radiosurgery) had resection with no tumor present, 4 improved (24 months, 43 months, 29 months, and 11 months) with subsequent follow-up, imaging one patient (123 months) has continued progression with planned resection, and one (19 months) has no available further follow-up. 2/7 pts had concurrent identification of new previously untreated lesions on cMRI that were hyperperfused. 3/7 patients had index lesions that were hyperperfused on VSASL-MRI. One patient (7 months after radiosurgery) had index lesion surgically confirmed as tumor, one (10 months) with further progression causing CNS death without further available treatment options, and one is alive with continued progression who elected supportive care. Two cases were particularly informative. One patient had sMRI progression of a previously stable lesion treated with radiosurgery 57 months earlier that was hyperperfused and at the same time a new untreated contrast enhancing lesion hyperperfused Which was confirmed on pathology to contain no tumor. Another patient with identification of a hypoperfused treated lesion 10 months after radiosurgery also had a new hyperperfused lesion that was then treated with radiosurgery. At 2 months follow-up, repeat VSASL-MRI demonstrated stability of the previously treated lesion whereas the radiosurgery treated new lesion converted to hypoperfused while still present on cMRI.

Conclusions: This pilot data supports study of the hypothesis that VSASL perfusion MRI may be useful in distinguishing tumor progression from radiation related imaging changes and/or be an early biomarker of radiosurgery response. We are initiating further study to refine the technique and assess the value of this approach in a larger number of patients.

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