Zero TE MRI applications to transcranial MR-guided focused ultrasound: Patient screening and treatment efficiency estimation.

BACKGROUND: The high acoustic impedance of the skull limits the performance of transcranial magnetic resonance-guided focused ultrasound (tcMRgFUS) therapy. Subject suitability screening is based on skull parameters estimated from computed tomography (CT) scans. PURPOSE: To assess the feasibility of screening for tcMRgFUS based on zero echo time (ZTE) MRI, and to explore the influence of measurable skull parameters in treatment performance. STUDY TYPE: Retrospective. POPULATION: Sixteen patients treated with tcMRgFUS thalamotomy for tremor. SEQUENCE: ZTE on a 3.0T GE scanner. ASSESSMENT: Baseline CT and ZTE images were processed to extract skull measures associated with treatment success: skull density ratio (SDR), skull thickness, and angle of incidence. Eight new metrics were proposed. CT and ZTE-based measures were compared. Each subject's energy-temperature curve was processed to extract a global estimate of efficiency and a measure of nonlinearity. These parameters were then correlated with the skull measures. STATISTICAL TESTS: Linear regression analysis to compare ZTE vs. CT-based measures, measures vs. efficiency, and measures vs. nonlinearity. Paired t-test to assess nonlinearity. RESULTS: CT and ZTE-based measures were significantly correlated (P < 0.01). In particular, classical metrics were robustly replicated (P < 0.001). The energy-temperature curves showed a nonlinear (logarithmic) relationship (P < 0.01). This nonlinearity was greater for thicker skulls (P < 0.01). Efficiency was correlated with skull thickness (P < 0.001) and SDR (P < 0.05). DATA CONCLUSION: The feasibility of ZTE-based screening has been proven, potentially making it possible to avoid ionizing radiation and the extra imaging session required for CT. The characterization of the influence that skull properties have on tcMRgFUS may serve to develop patient-specific heating models, potentially improving control over the treatment outcome. The relationship of skull thickness with efficiency and nonlinearity empowers the role of this metric in the definition of such models. In addition, the lower association of SDR with the energy-temperature curves emphasizes the need of revisiting this metric. LEVEL OF EVIDENCE: 3 Technical Efficacy: Stage 2 J. Magn. Reson. Imaging 2019;50:1583-1592.

PETER PHAN: An MRI phantom for the optimisation of radiomic studies of the female pelvis.

PURPOSE: To develop a phantom for methodological radiomic investigation on Magnetic Resonance (MR) images of female patients affected by pelvic cancer. METHODS: A pelvis-shaped container was filled with a MnCl2 solution reproducing the relaxation times (T1, T2) of muscle surrounding pelvic malignancies. Inserts simulating multi-textured lesions were embedded in the phantom. The relaxation times of muscle and tumour were measured on an MR scanner on healthy volunteers and patients; T1 and T2 of MnCl2 solutions were evaluated with a relaxometer to find the concentrations providing a match to in vivo relaxation times. Radiomic features were extracted from the phantom inserts and the patients' lesions. Their repeatability was assessed by multiple measurements. RESULTS: Muscle T1 and T2 were 1128 (806-1378) and 51 (40-65) ms, respectively. The phantom reproduced in vivo values within 13% (T1) and 12% (T2). T1 and T2 of tumour tissue were 1637 (1396-2121) and 94 (79-101) ms, respectively. The phantom insert best mimicking the tumour agreed within 7% (T1) and 24% (T2) with in vivo values. Out of 1034 features, 75% (95%) had interclass correlation coefficient greater than 0.9 on T1 (T2)-weighted images, reducing to 33% (25%) if the phantom was repositioned. The most repeatable features on phantom showed values in agreement with the features extracted from patients' lesions. CONCLUSIONS: We developed an MR phantom with inserts mimicking both relaxation times and texture of pelvic tumours. As exemplified with repeatability assessment, such phantom is useful to investigate features robustness and optimise the radiomic workflow on pelvic MR images.

ASAP (Automatic Software for ASL Processing): A toolbox for processing Arterial Spin Labeling images.

The method of Arterial Spin Labeling (ASL) has experienced a significant rise in its application to functional imaging, since it is the only technique capable of measuring blood perfusion in a truly non-invasive manner. Currently, there are no commercial packages for processing ASL data and there is no recognized standard for normalizing ASL data to a common frame of reference. This work describes a new Automated Software for ASL Processing (ASAP) that can automatically process several ASL datasets. ASAP includes functions for all stages of image pre-processing: quantification, skull-stripping, co-registration, partial volume correction and normalization. To assess the applicability and validity of the toolbox, this work shows its application in the study of hypoperfusion in a sample of healthy subjects at risk of progressing to Alzheimer's disease. ASAP requires limited user intervention, minimizing the possibility of random and systematic errors, and produces cerebral blood flow maps that are ready for statistical group analysis. The software is easy to operate and results in excellent quality of spatial normalization. The results found in this evaluation study are consistent with previous studies that find decreased perfusion in Alzheimer's patients in similar regions and demonstrate the applicability of ASAP.

Clinical and anatomical correlates of gait dysfunction in Alzheimer's disease.

We conducted a cross-sectional study to investigate the clinical and anatomical correlates of gait dysfunction in advanced Alzheimer's disease (AD). A comprehensive clinical protocol that included cognitive, functional, behavioral, and motor variables was administered to patients with probable AD (n = 100), possible AD (n = 17), and AD with cerebrovascular disease (AD + CVD) (n = 27). Gait dysfunction was evaluated with the Rating Scale for Gait Evaluation in Cognitive Deterioration and magnetic resonance imaging was analyzed in 94 patients (volumetry study) and 78 patients (diffusion tensor imaging study). Univariate correlations, multivariate regression, and statistical parametric mapping analyses were conducted in the total sample and in the subsample of patients with probable AD. Mean age was 82.5 (SD 6.3, range 56 to 98), 83.3% were female patients, and 95.1% displayed moderate to severe dementia. Parkinsonism, patient setting (nursing home), dementia severity, apathy, and (worse) cognitive performance significantly predicted gait dysfunction in the total sample (p < 0.05, R(2) = 0.58), whereas parkinsonism, patient setting, and limb weakness due to non-AD conditions predicted gait dysfunction in probable AD (p < 0.05, R(2) = 0.57). Gait dysfunction was related to atrophy in the motor cortex, the middle cingulate, the anterior insula, the right caudate (total sample only), and the anterior lobe of the cerebellum (p < 0.01, corrected). Significant correlations were also observed between gait dysfunction and damage in several white matter locations (p < 0.001, uncorrected). The present results are congruent with a model of multi-system gray matter degeneration, with progressive damage to critical regions (i.e., motor cortex, cingulate, insula, and cerebellum) producing gait dysfunction and, eventually, gait loss in AD.

Objective assessment of olfactory function using functional magnetic resonance imaging.

OBJECTIVE: To show the results of a device that generates automated olfactory stimuli suitable for functional magnetic resonance imaging (fMRI) experiments. MATERIAL AND METHODS: Ten normal volunteers, 5 women and 5 men, were studied. The system allows the programming of several sequences, providing the capability to synchronise the onset of odour presentation with acquisition by a trigger signal of the MRI scanner. The olfactometer is a device that allows selection of the odour, the event paradigm, the time of stimuli and the odour concentration. The paradigm used during fMRI scanning consisted of 15-s blocks. The odorant event took 2s with butanol, mint and coffee. RESULTS: We observed olfactory activity in the olfactory bulb, entorhinal cortex (4%), amygdala (2.5%) and temporo-parietal cortex, especially in the areas related to emotional integration. CONCLUSIONS: The device has demonstrated its effectiveness in stimulating olfactory areas and its capacity to adapt to fMRI equipment.