Visual pathway impairment by pituitary adenomas: quantitative diagnostics by diffusion tensor imaging.

OBJECTIVE Despite ample experience in surgical treatment of pituitary adenomas, little is known about objective indices that may reveal risk of visual impairment caused by tumor growth that leads to compression of the anterior visual pathways. This study aimed to explore diffusion tensor imaging (DTI) as a means for objective assessment of injury to the anterior visual pathways caused by pituitary adenomas. METHODS Twenty-three patients with pituitary adenomas, scheduled for transsphenoidal tumor resection, and 20 healthy control subjects were included in the study.

Impact of region-of-interest method on quantitative analysis of DTI data in the optic tracts.

Background: To extract DTI parameters from a specific structure, a region of interest (ROI) must be defined. ROI selection in small structures is challenging; the final measurement results could be affected due to the significant impact of small geometrical errors. In this study the optic tracts were analyzed with the aim to assess differences in DTI parameters due to ROI method and to identify the most reliable method.

Strengths and limitations of tractography methods to identify the optic radiation for epilepsy surgery.

Diffusion tensor imaging (DTI) tractography (TG) can visualize Meyer's loop (ML), providing important information for the epilepsy surgery team, both for preoperative counseling and to reduce the frequency of visual field defects after temporal lobe resection (TLR). This review highlights significant steps in the TG process, specifically the processing of raw data including choice of TG algorithm and the interpretation and validation of results. A lack of standardization of TG of the optic radiation makes study comparisons challenging.

Tractography of Meyer's loop for temporal lobe resection—validation by prediction of postoperative visual field outcome‬‬‬‬.

Background: Postoperative visual field defects are common after temporal lobe resection because of injury to the most anterior part of the optic radiation, Meyer's loop. Diffusion tensor tractography is a promising technique for visualizing the optic radiation preoperatively. The aim of this study was to assess the anatomical accuracy of Meyer's loop, visualized by the two most common tractography methods—deterministic (DTG) and probabilistic tractography (PTG)—in patients who had undergone temporal lobe resection.

Visualizing Meyer's loop: A comparison of deterministic and probabilistic tractography.

Background: Diffusion tensor tractography of the anterior extent of the optic radiation - Meyer's loop - prior to temporal lobe resection (TLR) may reduce the risk for postoperative visual field defect. Currently there is no standardized way to perform tractography.

Objective: To visualize Meyer's loop using deterministic (DTG) and probabilistic tractography (PTG) at different probability levels, with the primary aim to explore possible differences between methods, and the secondary aim to explore anatomical accuracy.

Optimal diffusion tensor imaging with repeated measurements.

Several data acquisition schemes for diffusion MRI have been proposed and explored to date for the reconstruction of the 2nd order tensor. Our main contributions in this paper are: (i) the definition of a new class of sampling schemes based on repeated measurements in every sampling point; (ii) two novel schemes belonging to this class; and (iii) a new reconstruction framework for the second scheme. We also present an evaluation, based on Monte Carlo computer simulations, of the performances of these schemes relative to known optimal sampling schemes for both 2nd and 4th order tensors.

On high order tensor-based diffusivity profile estimation.

Diffusion weighted magnetic resonance imaging (dMRI) is used to measure, in vivo, the self-diffusion of water molecules in biological tissues. High order tensors (HOTs) are used to model the apparent diffusion coefficient (ADC) profile at each voxel from the dMRI data. In this paper we propose: (i) A new method for estimating HOTs from dMRI data based on weighted least squares (WLS) optimization; and (ii) A new expression for computing the fractional anisotropy from a HOT that does not suffer from singularities and spurious zeros.

Ketoconazole-associated preferential increase in dopamine D2 receptor occupancy in striatum compared to pituitary in vivo: role for drug transporters?

Membrane transporters such as P-glycoprotein (P-gp) and breast cancer resistance protein (BCRP) are efflux pumps that remove drugs from the brain back to the peripheral blood compartment, serving as a functional component of the blood-brain barrier (BBB). We report here that coadministration of the P-gp and BCRP inhibitor ketoconazole with risperidone may preferentially increase D2 receptor occupancy in the striatum compared to pituitary. Four male patients with schizophrenia or schizoaffective disorder who had received at least 4 prior injections of the long-acting risperidone at a stable dose of 25 to 50 mg participated in this positron emission tomography study.