Understanding K trans: a simulation study based on a multiple-pathway model.

The transfer constant K trans is commonly employed in dynamic contrast-enhanced MRI studies, but the utility and interpretation of K trans as a potential biomarker of tumor vasculature remains unclear. In this study, computer simulations based on a comprehensive tracer kinetic model with multiple pathways was used to provide clarification on the interpretation and application of K trans. Tissue concentration-time curves pertaining to a wide range of transport conditions were simulated using the multiple-pathway (MP) model and fitted using the generalized kinetic (GK) and extended GK models. Relationships between K trans and plasma flow F p, vessel permeability PS and extraction rate EF p under various transport conditions were assessed by correlation and regression analysis. Results show that the MP model provides an alternative two-tier interpretation of K trans based on the vascular transit time. K trans is primarily associated with F p and EF p respectively, in the slow and rapid vascular transit states, independent of the magnitude of PS. The relative magnitudes of PS and F p only serve as secondary constraints for which K trans can be further associated with EF p and PS in the slow and rapid transit states, respectively.

Intravoxel incoherent motion and diffusion tensor imaging of early renal fibrosis induced in a murine model of streptozotocin induced diabetes.

INTRODUCTION: To assess if parameters in intravoxel incoherent motion (IVIM) and diffusion tensor imaging (DTI) can be used to evaluate early renal fibrosis in a mouse model of diabetic nephropathy. MATERIALS & METHODS: In a population of 38 male CD1 mice (8weeks old, 20-30g), streptozotocin induced diabetes was created in 20 mice via a single intraperitoneal injection of streptozotocin at 150mg/kg, while 18 mice served as control group. IVIM parameters were acquired at 0, 12 and 24weeks after injection of streptozotocin using a range of b values from 0 to 1200s/mm2. DTI parameters were obtained using 12 diffusion directions and lower b values of 0, 100 and 400s/mm2. DTI and IVIM parameters were obtained using region of interests drawn over the renal parenchyma. Histopathological analysis of the right kidney was performed in all mice. Results were analyzed using an unpaired t-test with P<0.05 considered statistically significant. RESULTS: Renal cortex fractional anisotropy (FA) was significantly lower in the diabetes group at week 12 as compared with the control group. Renal cortex apparent diffusion coefficient and tissue diffusivity were significantly higher in the diabetes group at week 12 compared with the control group at 12weeks. Blood flow was significantly decreased at the renal medulla at 24weeks. Histopathological analysis confirmed fibrosis in the diabetes group at 24weeks. CONCLUSION: FA is significantly reduced in diabetic nephropathy. FA might serve a potential role in the detection and therapy monitoring of early diabetic nephropathy.

Prognostic value of different CT measurements in early therapy response evaluation in patients with metastatic colorectal cancer.

OBJECTIVES: Patients with advanced stage colorectal carcinoma (CRC) display hepatic metastases on initial staging in up to 20% of cases. The effectiveness of chemotherapy is generally evaluated by computed tomography (CT) imaging using standardized criteria (RECIST). However, RECIST is not always optimal, and other criteria have been shown to correlate with pathologic response and overall survival. The aim of this study was to evaluate the prognostic value of different CT measurement for response assessment after initiation of chemotherapy in patients with synchronous colorectal cancer liver metastases. METHODS: Fifty-five patients with CRC and synchronous hepatic metastases were evaluated retrospectively at 2 academic centers. Different size, volume, ratio and attenuation parameters were determined at baseline and after 3 cycles of chemotherapy. The prognostic value of baseline measurements and of the change between baseline and second measurements was analyzed using Kaplan-Meier estimates. RESULTS: Median time to progression was 279 days, median overall survival was 704 days. In this selective patient population, neither a significant prognostic value of initial baseline CT parameters nor a prognostic value of the change between the first and the second CT measurements was found. CONCLUSION: Initial morphological response assessment using different CT measurements has no prognostic value concerning time to progression or overall survival in patients with synchronous colorectal liver metastases.

Accuracy of preoperative CT for local staging in colorectal carcinomas.

INTRODUCTION: This study aimed to determine the accuracy of computed tomography (CT) in the evaluation of local tumour invasion and regional lymphadenopathy in colorectal carcinomas. METHODS: A total of 99 consecutive patients who had undergone a contrast-enhanced CT within two weeks prior to surgery with histopathological confirmation of colorectal carcinoma were selected. Intravenous contrast-enhanced CT was performed with a 5-7 mm collimation. Axial images were retrospectively and independently reviewed by two radiologists (R1 and R2) who were blinded to the surgical findings and histopathology. The readers assessed the primary tumour according to modified CT staging criteria. The radiological assessment was then compared with the surgical findings and histopathology for accuracy and inter-observer agreement. RESULTS: At histopathology, the T-stage of the tumours was T2 in five, T3 in 62 and T4 in 32 patients, and the N-stage was N0 in 36, N1 in 28 and N2 in 35 patients. The accuracy of CT for T-stage and N-stage for the two readers was 45.5 percent and 60.6 percent (kappa is 0.30) and 33.3 percent and 45.4 percent (kappa is 0.23), respectively. The understaging and overstaging by R1 and R2 was 40.4 percent, 21.2 percent and 14.1 percent, 17.2 percent for T-stage and 22.2 percent, 37.4 percent and 32.3 percent, 28.3 percent for N-stage. The accuracy of serosal invasion for R1 and R2 (tumour perforates the visceral peritoneum or directly involves the adjacent organs) was 63.6 percent and 66.7 percent (kappa is 0.51), respectively. The understaging and overstaging by R1 and R2 for serosal invasion was 24.1 percent, 12.1 percent and 20.1 percent, 12.1 percent, respectively. CONCLUSION: Our study results show that the accuracy for CT staging of colorectal carcinomas for T-stage and in particular, serosal invasion, is moderate, but it is relatively low for N-stage.