Felipe P. G. Bergo

Interactive volume segmentation with differential image foresting transforms

The absence of object information very often asks for considerable human assistance in medical image segmentation. Many interactive two-dimensional and three-dimensional (3-D) segmentation methods have been proposed, but their response time to users actions should be considerably reduced to make them viable from the practical point of view. We circumvent this problem in the framework of the image foresting transform (IFT)-a general tool for the design of image operators based on connectivity-by introducing a new algorithm (DIFT) to compute sequences of IFTs in a differential way. We instantiate the DIFT algorithm for watershed-based and fuzzy-connected segmentations under two paradigms (single-object and multiple-object) and evaluate the efficiency gains of both approaches with respect to their linear-time implementation based on the nondifferential IFT. We show that the DIFT algorithm provides efficiency gains from 10 to 17, reducing the users waiting time for segmentation with 3-D visualization on a common PC from 19-36 s to 2-3 s. We also show that the multiple-object approach is more efficient than the single-object paradigm for both segmentation methods.

3T MRI Quantification of Hippocampal Volume and Signal in Mesial Temporal Lobe Epilepsy Improves Detection of Hippocampal Sclerosis

BACKGROUND AND PURPOSE: In mesial temporal lobe epilepsy, MR imaging quantification of hippocampal volume and T2 signal can improve the sensitivity for detecting hippocampal sclerosis. However, the current contributions of these analyses for the diagnosis of hippocampal sclerosis in 3T MRI are not clear. Our aim was to compare visual analysis, volumetry, and signal quantification of the hippocampus for detecting hippocampal sclerosis in 3T MRI. MATERIALS AND METHODS: Two hundred three patients with mesial temporal lobe epilepsy defined by clinical and electroencephalogram criteria had 3T MRI visually analyzed by imaging epilepsy experts. As a second step, we performed automatic quantification of hippocampal volumes with FreeSurfer and T2 relaxometry with an in-house software. MRI of 79 healthy controls was used for comparison. RESULTS: Visual analysis classified 125 patients (62%) as having signs of hippocampal sclerosis and 78 (38%) as having normal MRI findings. Automatic volumetry detected atrophy in 119 (95%) patients with visually detected hippocampal sclerosis and in 10 (13%) with visually normal MR imaging findings. Relaxometry analysis detected hyperintense T2 signal in 103 (82%) patients with visually detected hippocampal sclerosis and in 15 (19%) with visually normal MR imaging findings. Considered together, volumetry plus relaxometry detected signs of hippocampal sclerosis in all except 1 (99%) patient with visually detected hippocampal sclerosis and in 22 (28%) with visually normal MR imaging findings. CONCLUSIONS: In 3T MRI visually inspected by experts, quantification of hippocampal volume and signal can increase the detection of hippocampal sclerosis in 28% of patients with mesial temporal lobe epilepsy.

Structural brain abnormalities are related to retinal nerve fiber layer thinning and disease duration in neuromyelitis optica spectrum disorders

Background: Although aquaporin-4 (AQP4) is widely expressed in the human brain cortex, lesions are rare in neuromyelitis optica (NMO) spectrum disorders (NMOSD). Recently, however, several studies have demonstrated occult structural brain atrophy in NMO. Objective: This study aims to investigate magnetic resonance imaging (MRI) patterns of gray matter (GM) and white matter (WM) abnormalities in patients with NMOSD and to assess the visual pathway integrity during disease duration correlation of the retinal nerve fiber layer (RNFL) and pericalcarine cortex thickness. Methods: Twenty-one patients with NMOSD and 34 matched healthy controls underwent both high-field MRI (3T) high-resolution T1-weighted and diffusion-tensor MRI. Voxel-based morphometry, cortical analyses (Freesurfer) and diffusion-tensor imaging (DTI) analyses (TBSS-FSL) were used to investigate brain abnormalities. In addition, RNFL measurement by optic-coherence tomography (OCT) was performed. Results: We demonstrate that NMOSD is associated with GM and WM atrophy, encompassing more frequently the motor, sensory and visual pathways, and that the extent of GM atrophy correlates with disease duration. Furthermore, we demonstrate for the first time a correlation between RNFL and pericalcarine cortical thickness, with cortical atrophy evolving over the course of disease. Conclusions: Our findings indicate a role for retrograde and anterograde neurodegeneration in GM atrophy in NMOSD. However, the presence atrophy encompassing almost all lobes suggests that additional pathomechanisms might also be involved.

Frequent Seizures Are Associated with a Network of Gray Matter Atrophy in Temporal Lobe Epilepsy with or without Hippocampal Sclerosis

Objective Patients with temporal lobe epilepsy (TLE) with hippocampal sclerosis (HS) have diffuse subtle gray matter (GM) atrophy detectable by MRI quantification analyses. However, it is not clear whether the etiology and seizure frequency are associated with this atrophy. We aimed to evaluate the occurrence of GM atrophy and the influence of seizure frequency in patients with TLE and either normal MRI (TLE-NL) or MRI signs of HS (TLE-HS). Methods We evaluated a group of 172 consecutive patients with unilateral TLE-HS or TLE-NL as defined by hippocampal volumetry and signal quantification (122 TLE-HS and 50 TLE-NL) plus a group of 82 healthy individuals. Voxel-based morphometry was performed with VBM8/SPM8 in 3T MRIs. Patients with up to three complex partial seizures and no generalized tonic-clonic seizures in the previous year were considered to have infrequent seizures. Those who did not fulfill these criteria were considered to have frequent seizures. Results Patients with TLE-HS had more pronounced GM atrophy, including the ipsilateral mesial temporal structures, temporal lobe, bilateral thalami and pre/post-central gyri. Patients with TLE-NL had more subtle GM atrophy, including the ipsilateral orbitofrontal cortex, bilateral thalami and pre/post-central gyri. Both TLE-HS and TLE-NL showed increased GM volume in the contralateral pons. TLE-HS patients with frequent seizures had more pronounced GM atrophy in extra-temporal regions than TLE-HS with infrequent seizures. Patients with TLE-NL and infrequent seizures had no detectable GM atrophy. In both TLE-HS and TLE-NL, the duration of epilepsy correlated with GM atrophy in extra-hippocampal regions. Conclusion Although a diffuse network GM atrophy occurs in both TLE-HS and TLE-NL, this is strikingly more evident in TLE-HS and in patients with frequent seizures. These findings suggest that neocortical atrophy in TLE is related to the ongoing seizures and epilepsy duration, while thalamic atrophy is more probably related to the original epileptogenic process.

Dentate nuclei T2 relaxometry is a reliable neuroimaging marker in Friedreich's ataxia

In Friedreichs ataxia (FRDA), frataxin deficiency results in iron redistribution in the dentate nuclei (DNC). Clusters of iron cause inhomogeneities in a magnetic field and result in a reduction in T2 relaxation time (T2).

Spinal cord atrophy correlates with disease duration and severity in amyotrophic lateral sclerosis.

Abstract Our objective was to investigate spinal cord (SC) atrophy in amyotrophic lateral sclerosis (ALS) patients, and to determine whether it correlates with clinical parameters. Forty-three patients with ALS (25 males) and 43 age- and gender-matched healthy controls underwent MRI on a 3T scanner. We used T1-weighted 3D images covering the whole brain and the cervical SC to estimate cervical SC area and eccentricity at C2/C3 level using validated software (SpineSeg). Disease severity was quantified with the ALSFRS-R and ALS Severity scores. SC areas of patients and controls were compared with a Mann-Whitney test. We used linear regression to investigate association between SC area and clinical parameters. Results showed that mean age of patients and disease duration were 53.1 ± 12.2 years and 34.0 ± 29.8 months, respectively. The two groups were significantly different regarding SC areas (67.8 ± 6.8 mm² vs. 59.5 ± 8.4 mm², p < 0.001). Eccentricity values were similar in both groups (p = 0.394). SC areas correlated with disease duration (r = − 0.585, p < 0.001), ALSFRS-R score (r = 0.309, p = 0.044) and ALS Severity scale (r = 0.347, p = 0.022). In conclusion, patients with ALS have SC atrophy, but no flattening. In addition, SC areas correlated with disease duration and functional status. These data suggest that quantitative MRI of the SC may be a useful biomarker in the disease.

Image segmentation by tree pruning

The image foresting transform (IFT) has been proposed for the design of image operators based on connectivity. The IFT reduces image processing problems into a minimum-cost path forest problem in a graph derived from the image. It has been successfully used for image filtering, segmentation, and analysis. In this work, we propose a novel image operator which solves segmentation by pruning trees of the forest. First, an IFT is applied to create an optimum-path forest whose roots are pixels selected inside a desired object. In this forest, the background consists of a few subtrees rooted at pixels on the objects boundary. These boundary pixels are identified and their subtrees are eliminated, such that the remaining forest defines the object. The tree pruning is an effective alternative to situations where image segmentation methods based on competing seeds fail. We present an interactive implementation of the tree-pruning technique, show several examples and discuss some experiments toward fully automatic segmentation.

Amygdala enlargement occurs in patients with mesial temporal lobe epilepsy and hippocampal sclerosis with early epilepsy onset

Mesial temporal lobe epilepsy (MTLE) associated with hippocampal sclerosis (HS) is considered an electroclinical syndrome, and there is a debate whether it is a unique disease or an entity with distinct subtypes. Together with other mesial temporal structures, the amygdala is important in the epileptogenic network of patients with MTLE with HS. During automatic volumetric analysis of mesial structures in a group of 102 patients with MTLE with MRI signs of HS, we observed significant amygdala enlargement in 14 (14%) individuals compared to a group of 79 healthy subjects. The increased amygdala volume was contralateral to the epileptogenic zone and MRI signs of HS in 93% of these patients. Patients with MTLE with HS and enlarged amygdala had significantly earlier epilepsy onset than those without an increase of amygdala volumes. Mesial temporal lobe epilepsy with HS and enlarged amygdala may be a part of the spectrum of this condition.

FCD segmentation using texture asymmetry of MR-T1 images of the brain

Focal cortical dysplasia is the most common malformation in patients with intractable epilepsy. The segmentation of FCD lesions in MR-T1 images of the brain is a crucial step for treatment planning. In this work we present a new FCD segmentation technique based on analysis of texture asymmetry. This technique does not rely on template-based segmentation and is applicable to patients of any age, regardless of anatomic variations. We evaluated the method on 5 patients (aged 1 ly-51y), and obtained 100% detection rate and coverage of 76.9% of the lesional voxels.

Aberrant topological patterns of brain structural network in temporal lobe epilepsy

Although altered large‐scale brain network organization in patients with temporal lobe epilepsy (TLE) has been shown using morphologic measurements such as cortical thickness, these studies, have not included critical subcortical structures (such as hippocampus and amygdala) and have had relatively small sample sizes. Here, we investigated differences in topological organization of the brain volumetric networks between patients with right TLE (RTLE) and left TLE (LTLE) with unilateral hippocampal atrophy.