Non-contrast based approach for liver function quantification using Bayesian-based intravoxel incoherent motion diffusion weighted imaging: A pilot study.

PURPOSE: Liver cirrhosis disrupts liver function and tissue perfusion, detectable by magnetic resonance imaging (MRI). Assessing liver function at the voxel level with 13-b value intravoxel incoherent motion diffusion-weighted imaging (IVIM-DWI) could aid in radiation therapy liver-sparing treatment for patients with early impairment. This study aimed to evaluate the feasibility of IVIM-DWI for liver function assessment and correlate it with other multiparametric (mp) MRI methods at the voxel level. METHOD: This study investigates the variability of apparent diffusion coefficient (ADC) derived from 13-b value IVIM-DWI and B1-corrected dual flip angle (DFA) T1 mapping. Experiments were conducted in-vitro with QIBA and NIST phantoms and in 10 healthy volunteers for IVIM-DWI. Additionally, 12 patients underwent an mp-MRI examination. The imaging protocol included a 13-b value IVIM-DWI sequence for generating IVIM parametric maps. B1-corrected DFA T1 pulse sequence was used for generating T1 maps, and Gadoxatate low temporal resolution dynamic contrast-enhanced (LTR-DCE) MRI was used for generating the Hepatic extraction fraction (HEF) map. The Mann-Whitney U test was employed to compare IVIM-DWI parameters (Pure Diffusion, Dslow ; Pseudo diffusion, Dfast ; and Perfusion Fraction, Fp ) between the healthy volunteer and patient groups. Furthermore, in the patient group, statistical correlations were assessed at a voxel level between LTR-DCE MRI-derived HEF, T1 post-Gadoxetate administration, ΔT1%, and various IVIM parameters using Pearson correlation. RESULTS: For-vitro measurements, the maximum coefficient of variation of the ADC and T1 parameters was 12.4% and 16.1%, respectively. The results also showed that Fp and Dfast were able to distinguish between healthy liver function and mild liver function impairment at the global level, with p = 0.002 for Fp and p < 0.001 for Dfast . Within the patient group, these parameters also exhibited a moderate correlation with HEF at the voxel level. CONCLUSION: Overall, the study highlighted the potential of Dfast and Fp for detecting liver function impairment at both global and pixel levels.

Voxel-based supervised machine learning of peripheral zone prostate cancer using noncontrast multiparametric MRI.

PURPOSE: The aim of this study was to develop and assess the performance of supervised machine learning technique to classify magnetic resonance imaging (MRI) voxels as cancerous or noncancerous using noncontrast multiparametric MRI (mp-MRI), comprised of T2-weighted imaging (T2WI), diffusion-weighted imaging (DWI), and advanced diffusion tensor imaging (DTI) parameters. MATERIALS AND METHODS: In this work, 191 radiomic features were extracted from mp-MRI from prostate cancer patients. A comprehensive set of support vector machine (SVM) models for T2WI and mp-MRI (T2WI + DWI, T2WI + DTI, and T2WI + DWI + DTI) were developed based on novel Bayesian parameters optimization method and validated using leave-one-patient-out approach to eliminate any possible overfitting. The diagnostic performance of each model was evaluated using the area under the receiver operating characteristic curve (AUROC). The average sensitivity, specificity, and accuracy of the models were evaluated using the test data set and the corresponding binary maps generated. Finally, the SVM plus sigmoid function of the models with the highest performance were used to produce cancer probability maps. RESULTS: The T2WI + DWI + DTI models using the optimal feature subset achieved the best performance in prostate cancer detection, with the average AUROC , sensitivity, specificity, and accuracy of 0.93 ± 0.03, 0.85 ± 0.05, 0.82 ± 0.07, and 0.83 ± 0.04, respectively. The average diagnostic performance of T2WI + DTI models was slightly higher than T2WI + DWI models (+3.52%) using the optimal radiomic features. CONCLUSIONS: Combination of noncontrast mp-MRI (T2WI, DWI, and DTI) features with the framework of a supervised classification technique and Bayesian optimization method are able to differentiate cancer from noncancer voxels with high accuracy and without administration of contrast agent. The addition of cancer probability maps provides additional functionality for image interpretation, lesion heterogeneity evaluation, and treatment management.

Cerebrospinal fluid absorption block at the vertex in chronic hydrocephalus: obstructed arachnoid granulations or elevated venous pressure?

BACKGROUND: The lack of absorption of CSF at the vertex in chronic hydrocephalus has been ascribed to an elevation in the arachnoid granulation outflow resistance (Rout). The CSF infusion studies measuring Rout are dependent on venous sinus pressure but little is known about the changes in pressure which occur throughout life or with the development of hydrocephalus. METHODS: Twenty patients with chronic hydrocephalus underwent MR venography and MR flow quantification techniques. The venous outflow pressure was estimated from the sinus blood flow and the cross-sectional area of the transverse sinuses. Adult controls as well as a normal young cohort were selected to estimate the change in sinus pressure which occurs throughout life and following the development of hydrocephalus. Significance was tested with a Student's t-test. RESULTS: The size of the transverse sinuses was unchanged from the 1(st) to the 5(th) decade of life, indicating a stable outflow resistance. However, the blood flow was reduced by 42%, indicating a likely similar reduction in pressure gradient across the sinuses. The sinuses of hydrocephalus patients were 38% smaller than matched controls, indicating a 2.5 times increase in resistance. Despite the 24% reduction in blood flow, a significant increase in sinus pressure is suggested. CONCLUSIONS: The size of the venous sinuses normally does not change over the age range investigated but sinus pressure is reduced proportional to an age-related blood flow reduction. Hydrocephalus is associated with much smaller sinuses than normal and an elevation in venous pressure may explain the lack of CSF absorption into the arachnoid granulations in chronic hydrocephalus.

Idiopathic hydrocephalus in children and idiopathic intracranial hypertension in adults: two manifestations of the same pathophysiological process?

OBJECT: Both idiopathic intracranial hypertension (IIH) in adults and idiopathic hydrocephalus in children have been shown to involve elevations in venous pressure that resolve once the cerebrospinal fluid pressure is reduced. It has been assumed that the venous pressure elevations in both conditions are not hemodynamically significant, but measurement of venous collateral flow in IIH has shown these pressure elevations to be of consequence. The authors used the same methodology to see if the venous pressure elevations noted in childhood hydrocephalus are important. METHODS: Fourteen patients with idiopathic childhood hydrocephalus underwent magnetic resonance imaging with flow quantification. The degree of ventricular enlargement, total blood inflow, and superior sagittal/straight sinus outflow was measured. The degree of collateral venous flow was calculated for each venous territory. The findings were compared with findings in 14 age-matched controls. RESULTS: In children with hydrocephalus the cerebral blood inflow was normal, but the superior sagittal sinus (SSS) and straight sinus outflows were reduced by 27% and 38%, respectively, compared with measurements in controls (p = 0.03 and 0.002). These findings suggest that approximately 150 ml of blood per minute was returning via collateral channels from that portion of the brain drained by the SSS, and 60 ml/minute was returning from collaterals in the deep venous territory. CONCLUSIONS: Similarly to patients with IIH, children with hydrocephalus show a significant elevation in collateral venous flow, indicating that the same venous pathophysiological process may be operating in both conditions. Whether or not the ventricles dilate may depend on the differences in brain compliance between adults and children.

Perfusion computed tomography: prediction of final infarct extent and stroke outcome.

The Alberta Stroke Program Early Computed Tomography Score (ASPECTS) has not been previously applied to perfusion CT (CTP). Five raters assigned ASPECTS to baseline noncontrast CT (NCCT), CT angiography source images (CTA-SI), CTP source images (CTP-SI), and CTP maps of cerebral blood volume (CBV), cerebral blood flow (CBF), and mean transit time (MTT) from 37 consecutive patients with less than 6-hour anterior circulation ischemic stroke. Major reperfusion was identified on follow-up imaging. Mean baseline ASPECTS was compared with follow-up imaging ASPECTS. Rates of favorable outcome were compared for dichotomized baseline ASPECTS. In patients with major reperfusion, mean CBV and CTP-SI ASPECTS closely predicted final infarct ASPECTS. In patients without major reperfusion, mean CBF and MTT ASPECTS best predicted final infarct ASPECTS. There were significant increases in rates of favorable outcome for CTP-SI and CBV ASPECTS of greater than 6, versus less than or equal to 6, but not for other baseline CT modalities. ASPECTS applied to CTP is more accurate at identifying the extent of reversible and irreversible ischemia and at predicting final clinical outcome than NCCTor CTA-SI.