Therapeutic response is evaluated using the diameter of tumors and quantitative parameters of 2-[18F] fluoro-2-deoxy-d-glucose positron emission tomography (FDG-PET). Tumor response to molecular-targeted drugs and immune checkpoint inhibitors is different from conventional chemotherapy in terms of temporal metabolic alteration and morphological change after the therapy. Cancer stem cells, immunologically competent cells, and metabolism of cancer are considered targets of novel therapy. Accumulation of FDG reflects the glucose metabolism of cancer cells as well as immune cells in the tumor microenvironment, which differs among patients according to the individual immune function; however, FDG-PET could evaluate the viability of the tumor as a whole. On the other hand, specific imaging and cell tracking of cancer cell or immunological cell subsets does not elucidate tumor response in a complexed interaction in the tumor microenvironment. Considering tumor heterogeneity and individual variation in therapeutic response, a radiomics approach with quantitative features of multimodal images and deep learning algorithm with reference to pathologic and genetic data has the potential to improve response assessment for emerging cancer therapy.
Thirty-seven magnetic resonance (MR) examinations were performed at 0.5 T in 33 patients with subarachnoid hemorrhage (SAH) caused by a ruptured aneurysm. Images were obtained 2 hours to 75 days after the ictus. Twenty-four proton-density-weighted (long repetition time [TR], short echo time [TE]) images were obtained in the acute stage (< 72 hours after the ictus) of SAH; SAH was hyperintense to brain parenchyma and cerebrospinal fluid in all cases. The detectability of acute SAH on T1- (short TR, short TE) and T2- (long TR, long TE) weighted images was 36% and 50%, respectively. In the subacute and chronic stages (> 3 days after the ictus), the detectability of SAH on T1-, T2-, and proton-density-weighted images was 73%, 31%, and 83%, respectively. Although computed tomography is still the modality of choice for evaluating acute SAH, the authors emphasize that even acute SAH can be reliably demonstrated with MR imaging with the appropriate parameters.
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