Monitoring therapeutic interventions in cancer and stroke using quantitative magnetic resonance imaging.

摘要

Conventional nuclear magnetic resonance imaging (MRI) techniques provide excellent qualitative insights into the human body not possible with other imaging modalities. However, in order to monitor the efficacy of therapeutic interventions, quantitative imaging techniques are necessary. Quantitative imaging techniques provide numeric results needed for objective evaluation of treatment strategies as well as spatial localization. MRI techniques were developed to spatially map and quantify murine tumor oxygenation following therapeutic interventions. MRI techniques were also developed to map regional changes in the apparent diffusion coefficient (ADC) during experimental focal ischemia in the rat brain following middle cerebral arterial occlusion.; Oxygen levels in neoplasms are below those of normal tissue rendering neoplastic tissue radioresistant. Monitoring oxygen tension should provide valuable insights into the proper time course of overcoming hypoxia, thereby enhancing the efficacy of radiation therapy. There is no known acceptable non-invasive measurement technique to measure tissue oxygenation. Noninvasive oxygen tension images (maps) of murine fibrosarcoma tumors were generated in vivo using {dollar}rmsp{lcub}19{rcub}F{dollar} relaxometry of perfluorocarbon emulsions in conjunction with inversion-recovery echo-planar imaging. Tumor oxygen tension was monitored following carbogen breathing, nicotinamide injections, and radiation therapy. Tumor oxygenation increased by 6 {dollar}pm{dollar} 2 torr following carbogen breathing, by 4 {dollar}pm{dollar} 2 torr one hour following nicotinamide administration and decreased by 9 {dollar}pm{dollar} 1 torr 1-3 hours post radiation therapy.; Diffusion-weighted magnetic resonance imaging (DWI) is a useful method for visualizing early cerebral ischemia and is proving to be an important tool for monitoring the progress and treatment of the disease in animal models. The hyperintensity observed in a DWI reflects a decrease in the ADC of water in the ischemic region. ADC values are reduced in the first few hours following ischemic injury. Diffusion-weighted echo-planar imaging (DW-EPI) was used to construct spatial maps where the pixel intensity was a measure of the absolute ADC value. Multiple ADC maps were collected post induction of stroke and were later correlated to postmortem infarct. Regions where ADC values fell below 0.55 {dollar}times{dollar} {dollar}10sp{lcub}-5{rcub}{dollar} {dollar}rm cmsp2/s{dollar} at 2 hours post-occlusion were highly correlated to infarct areas identified by postmortem histological staining 24 hours post-occlusion. ADC maps were also constructed to monitor the temporal evolution of ischemic volume and to monitor reperfusion therapy.