Oncologic patient care and clinical trials are increasingly relying on radiological images for the assessment of therapy response. Currently, the radiological assessment of therapy response is predominantly based on tumor size changes measured using methods such as the Response Evaluation Criteria in Solid Tumors (RECIST) or Response Assessment in Neuro-Oncology (RANO). This is a major limiting factor as the effects of many therapeutic agents at the microscopic level precede the eventual changes in tumor size.
Shown: Representative cerebral blood flow (CBF) maps acquired using our optimized 3D pCASL with CASPR (middle column) and 3D pCASL with GraSE (right column), compared to standard structural T2-weighted images (left column) of a 72-year-old GBM patient. CASPR acquisition shows improved robustness to B0 inhomogeneities that can be readily overlaid on structural images for extracting quantitative tumor values. Solid arrow shows the tumor, and the dashed arrow shows image distortion on 3D GRASE ASL image.
One of the microscopic tumor properties that has gained increased attention is angiogenesis, which is well recognized to support tumor proliferation and infiltration. Among various methods to measure angiogenesis (i.e., tumor blood supply), arterial spin-labeled (ASL) magnetic resonance imaging (MRI) has emerged as a promising method. Unlike other perfusion-weighted imaging techniques such as positron emission tomography (PET) using 15O-labeled water (15O-PET), 99mTc-labeled single-photon emission computed tomography (SPECT), or iodine-based contrast-enhanced computed tomography (CT), MRI does not involve ionizing radiation. Furthermore, compared to dynamic contrast enhanced (DCE) MRI and dynamic susceptibility contrast (DSC) MRI, ASL-MRI uses water as the endogenous tracer and does not require the injection of gadolinium-based contrast agents. Hence, ASL-MRI is well-suited for longitudinal monitoring of cancer patients without the concerns of nephrogenic systemic fibrosis, gadolinium deposition, or cumulative radiation exposure.
As part of our NIH/NCI funded quantitative imaging network U01 grant, we are evaluating robust ASL techniques (Greer JS et. al. Magn. Reson Med. 2019) for the longitudinal assessment of therapy response in patients with glioblastoma (Zhou L et. al. Tomography 2020) or metastatic kidney cancer.
Shown: Bland-Altman analysis showing improved robustness of 3D pCASL using CASPR with no significant bias between two separate acquisitions. 95% confidence intervals of the agreement are shown in red dashed line. Left plot shows cerebral blood flow (CBF) values from normal appearing grey matter (NAGM) and the right plot shows CBF values from tumors, suggesting good agreement with minimal bias.