The challenge of mapping the human connectome based on diffusion tractography

Tractography based on non-invasive diffusion imaging is central to the study of human brain connectivity. To date, the approach has not been systematically validated in ground truth studies. Based on a simulated human brain data set with ground truth tracts, we organized an open international tractography challenge, which resulted in 96 distinct submissions from 20 research groups. Here, we report the encouraging finding that most state-of-the-art algorithms produce tractograms containing 90% of the ground truth bundles (to at least some extent). However, the same tractograms contain many more invalid than valid bundles, and half of these invalid bundles occur systematically across research groups. Taken together, our results demonstrate and confirm fundamental ambiguities inherent in tract reconstruction based on orientation information alone, which need to be considered when interpreting tractography and connectivity results. Our approach provides a novel framework for estimating reliability of tractography and encourages innovation to address its current limitations.

Though tractography is widely used, it has not been systematically validated. Here, authors report results from 20 groups showing that many tractography algorithms produce both valid and invalid bundles.

A test-retest study on Parkinson's PPMI dataset yields statistically significant white matter fascicles

In this work, we propose a diffusion MRI protocol for mining Parkinson's disease diffusion MRI datasets and recover robust disease-specific biomarkers. Using advanced high angular resolution diffusion imaging (HARDI) crossing fiber modeling and tractography robust to partial volume effects, we automatically dissected 50 white matter (WM) fascicles. These fascicles connect deep nuclei (thalamus, putamen, pallidum) to different cortical functional areas (associative, motor, sensorimotor, limbic), basal forebrain and substantia nigra. Then, among these 50 candidate WM fascicles, only the ones that passed a test-retest reproducibility procedure qualified for further tractometry analysis. Leveraging the unique 2-timepoints test-retest Parkinson's Progression Markers Initiative (PPMI) dataset of over 600 subjects, we found statistically significant differences in tract profiles along the subcortico-cortical pathways between Parkinson's disease patients and healthy controls. In particular, significant increases in FA, apparent fiber density, tract-density and generalized FA were detected in some locations of the nigro-subthalamo-putaminal-thalamo-cortical pathway. This connection is one of the major motor circuits balancing the coordination of motor output. Detailed and quantifiable knowledge on WM fascicles in these areas is thus essential to improve the quality and outcome of Deep Brain Stimulation, and to target new WM locations for investigation.

Fiber tractography using machine learning

We present a fiber tractography approach based on a random forest classification and voting process, guiding each step of the streamline progression by directly processing raw diffusion-weighted signal intensities. For comparison to the state-of-the-art, i.e. tractography pipelines that rely on mathematical modeling, we performed a quantitative and qualitative evaluation with multiple phantom and in vivo experiments, including a comparison to the 96 submissions of the ISMRM tractography challenge 2015. The results demonstrate the vast potential of machine learning for fiber tractography.

Recognition of white matter bundles using local and global streamline-based registration and clustering

Virtual dissection of diffusion MRI tractograms is cumbersome and needs extensive knowledge of white matter anatomy. This virtual dissection often requires several inclusion and exclusion regions-of-interest that make it a process that is very hard to reproduce across experts. Having automated tools that can extract white matter bundles for tract-based studies of large numbers of people is of great interest for neuroscience and neurosurgical planning. The purpose of our proposed method, named RecoBundles, is to segment white matter bundles and make virtual dissection easier to perform. This can help explore large tractograms from multiple persons directly in their native space. RecoBundles leverages latest state-of-the-art streamline-based registration and clustering to recognize and extract bundles using prior bundle models. RecoBundles uses bundle models as shape priors for detecting similar streamlines and bundles in tractograms. RecoBundles is 100% streamline-based, is efficient to work with millions of streamlines and, most importantly, is robust and adaptive to incomplete data and bundles with missing components. It is also robust to pathological brains with tumors and deformations. We evaluated our results using multiple bundles and showed that RecoBundles is in good agreement with the neuroanatomical experts and generally produced more dense bundles. Across all the different experiments reported in this paper, RecoBundles was able to identify the core parts of the bundles, independently from tractography type (deterministic or probabilistic) or size. Thus, RecoBundles can be a valuable method for exploring tractograms and facilitating tractometry studies.

An Infinite Restricted Boltzmann Machine

We present a mathematical construction for the restricted Boltzmann machine (RBM) that does not require specifying the number of hidden units. In fact, the hidden layer size is adaptive and can grow during training. This is obtained by first extending the RBM to be sensitive to the ordering of its hidden units. Then, with a carefully chosen definition of the energy function, we show that the limit of infinitely many hidden units is well defined. As with RBM, approximate maximum likelihood training can be performed, resulting in an algorithm that naturally and adaptively adds trained hidden units during learning. We empirically study the behavior of this infinite RBM, showing that its performance is competitive to that of the RBM, while not requiring the tuning of a hidden layer size.

Tractometer: online evaluation system for tractography

We have developed a tractometer: an online evaluation system for tractography processing pipelines. One can now evaluate the end effects on fiber tracts of different acquisition parameters (b-value, number of directions, denoising or not, averaging or not), different local estimation techniques (tensor, q-ball, spherical deconvolution, spherical wavelets) and to different tractography parameters (masking, seeding, stopping criteria). At this stage, the system is solely based on a revised FiberCup analysis, but we hope that the community gets involved and provides us with new phantoms, new algorithms, third party libraries and new geometrical metrics, to name a few. We believe that the new connectivity analysis and tractography characteristics proposed can highlight limits of the algorithms and contribute in elucidating the open questions in fiber tracking: from raw data to connectivity analysis.

Parents' attitudes, knowledge, and behavior toward youth gambling: a five-year follow-up

This study compares the attitudes, knowledge, and behavior of parents of 5- to 17-year-old children regarding youth gambling. This information was obtained through two telephone surveys conducted in 1995, and 5 years later in 2000, in the Québec City area. Survey 1, in 1995, was conducted on 279 respondents, while survey 2, in 2000, was carried out with 213 respondents. Results showed a number of changes in parents' attitudes, behavior, and knowledge concerning youth gambling: For example, parents' perception of the age of onset of gambling behavior had improved slightly at the end of the 5-year period. Furthermore, parents were more satisfied with government limitation of access to gambling, and more accurately informed about legal aspects of the sale of lottery tickets. However, the percentage of parents who failed to associate youth gambling with some of its correlates (arcade attendance, parental gambling problems, and friendship with gamblers) increased from 1995 to year 2000. The improvements that were observed suggested that parents had benefited from media-transmitted information during this period. However, the deterioration of some parental attitudes, and the stability of other variables, suggest that it is still important to educate parents about youth gambling, and to design interventions adapted to parents' needs.

Extensive lower eyelid pigment spread after blepharopigmentation

PURPOSE

To report on a complication of blepharopigmentation.

METHODS

Case report.

RESULTS

An 81-year-old woman underwent cosmetic tattooing of all four eyelids. The pigment immediately spread from the right lower eyelid lash line to the nasojugal fold. The dispersion was so extensive in surface area that nonsurgical techniques for ameliorating the dispersion would not be effective. The unintentionally tattooed skin was excised and reconstructed with a lateral canthal suspension and full thickness skin grafts. Pathologic examination of the excised tissue revealed pigmentation of all layers of the skin and the surface of the orbicularis muscle.

CONCLUSION

This case illustrates that extensive pigment spread following blepharopigmentation may require extensive reconstruction to correct the problem.

Keratohematoma leading to acquired posterior keratoconus

We describe a patient with congenital syphilis associated with corneal neovascularization and subsequent intracorneal hemorrhage. Over time, this condition resulted in acquired posterior keratoconus. A review of our clinical case, the literature, and histologic findings is presented. To our knowledge, this is the first reported case of acquired posterior keratoconus associated with corneal vascularization and hemorrhage secondary to congenital syphilis. We also have provided histopathologic evidence for the prescence of an iron ring.

The role of histopathology in the diagnosis and management of uveitis

Intraocular inflammation/uveitis is one of the more poorly understood areas in the field of ophthalmology. We hope to improve this understanding by first reviewing the classic histopathologic approach to intraocular inflammation, and then by integrating that with the current role of histopathology in the diagnosis and management of uveitis. Herein, we will present a systematic approach, beginning with the most accessible conjunctival, lacrimal gland and lymph node biopsy sites; extending through anterior chamber tap, iris biopsy, and vitrectomy and ending with retinal or chorioretinal biopsy of distant organ sites. We will show how a combination of these histopathologic elements can aid in the diagnosis, and thereby the management, of intraocular inflammations and uveitis.

Depressant effect on the retrograde atrioventricular nodal conduction of beta-adrenergic blockade by propranolol in humans

Propranolol is known to have a depressant effect on anterograde atrioventricular (AV) nodal conduction in normal subjects and in those with AV nodal reentrant tachycardia. Using His bundle recording and programmed ventricular stimulation, the effect of propranolol-induced beta-adrenergic blockade (1 mg/kg intravenously) on retrograde AV nodal conduction was studied in 17 patients without (group I) and nine with (group II) AV nodal reentrant tachycardia. During baseline studies the ventricular pacing cycle length that induced ventriculoatrial block was 338 +/- 60 ms (range 260 to 450 ms) in group I and 305 +/- 39 ms (range 260 to 375 ms) in group II patients (not significant). After injection of propranolol, the ventricular pacing cycle length that induced ventriculoatrial block in group I patients was 416 +/- 97 ms (range 300 to 550 ms) (P less than 0.001, compared to baseline state) in 15 patients, and complete block occurred in two patients. In group II patients ventriculoatrial block occurred at a ventricular pacing cycle length of 375 +/- 97 ms (range 260 to 510 ms) (P less than 0.02 compared to baseline value) in eight patients, and complete block occurred in one patient. Retrograde AV nodal conduction expressed as the H2A2 interval was 75 +/- 33 ms (range 35 to 150 ms) in group I and 49 +/- 16 ms (range 20 to 80 ms) in group II patients (P less than 0.05). Following the administration of propranolol, the H2A2 interval was prolonged in group I patients by 10 to 45 ms in 11 patients, no retrograde AV nodal conduction was observed in three patients, and there was no effect in two patients.(ABSTRACT TRUNCATED AT 250 WORDS)

Acute Heinz-body anemia due to severe cresol poisoning: successful treatment with erythrocytapheresis

A patient with massive intravascular Heinz-body hemolytic anemia associated with the presence of bizarre-looking erythrocytes following the oral ingestion of approximately 100 mL of "penetrating oil", a petroleum distillate containing 85% kerosene, 12% cresol and 2% surfactant, is described. He was treated successfully with immediate erythrocytapheresis and forced diuresis.