MR tractography with diffusion tensor imaging in clinical routine

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.

METHODS

Eight patients with temporal lobe resection for temporal lobe pathology were included. Perimetry and diffusion tensor imaging were performed pre- and postoperatively. Two independent operators analyzed the distance between the temporal pole and Meyer's loop (TP-ML) using DTG and PTG. Results were compared to each other, to data from previously published dissection studies and to postoperative perimetry results. For the latter, Spearman's rank correlation coefficient (r(s)) was used.

RESULTS

Median preoperative TP-ML distances for nonoperated sides were 42 and 35 mm, as determined by DTG and PTG, respectively. TP-ML assessed with PTG was a closer match to dissection studies. Intraclass correlation coefficients were 0.4 for DTG and 0.7 for PTG. Difference between preoperative TP-ML (by DTG and PTG, respectively) and resection length could predict the degree of postoperative visual field defects (DTG: r(s) = -0.86, p < 0.05; PTG: r(s) = -0.76, p < 0.05).

CONCLUSION

Both DTG and PTG could predict the degree of visual field defects. However, PTG was superior to DTG in terms of reproducibility and anatomical accuracy. PTG is thus a strong candidate for presurgical planning of temporal lobe resection that aims to minimize injury to Meyer's loop.

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. We discuss results showing differences between studies and uncertainties large enough to be of clinical relevance and present implications of this technique for temporal lobe epilepsy surgery. Recent studies in temporal lobe epilepsy patients, employing TG intraoperatively, show promising results in reduction of visual field defects, with maintained seizure reduction.

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.

METHODS

Twenty-three diffusion tensor imaging exams (11 controls and 7 TLR-patients, pre- and post-surgical) were analyzed using DTG and PTG thresholded at probability levels 0.2%, 0.5%, 1%, 5% and 10%. The distance from the tip of the temporal lobe to the anterior limit of Meyer's loop (TP-ML) was measured in 46 optic radiations. Differences in TP-ML between the methods were compared. Results of the control group were compared to dissection studies and to a histological atlas.

RESULTS

For controls and patients together, there were statistically significant differences (p<0.01) for TP-ML between all methods thresholded at PTG ≤1% compared to all methods thresholded at PTG ≥5% and DTG. There were no statistically significant differences between PTG 0.2%, 0.5% and 1% or between PTG 5%, 10% and DTG. For the control group, PTG ≤1% showed a closer match to dissection studies and PTG 1% showed the best match to histological tracings of Meyer's loop.

CONCLUSIONS

Choice of tractography method affected the visualized location of Meyer's loop significantly in a heterogeneous, clinically relevant study group. For the controls, PTG at probability levels ≤1% was a closer match to dissection studies. To determine the anterior extent of Meyer's loop, PTG is superior to DTG and the probability level of PTG matters.

DIFFUSION-WEIGHTED MAGNETIC RESONANCE IMAGING OF THE ULNAR NERVE IN CUBITAL TUNNEL SYNDROME

Diffusion-weighted images based on magnetic resonance reveal the microstructure of tissues by monitoring the random movement of water molecules. In this study, we investigated whether this new technique could visualize pathologic lesions on ulnar nerve in cubital tunnel. Six elbows in six healthy males without any symptoms and eleven elbows in ten patients with cubital tunnel syndrome underwent on diffusion-weighted MRI. No signal from the ulnar nerve was detected in normal subjects. Diffusion-weighted MRI revealed positive signals from the ulnar nerve in all of the eleven elbows with cubital tunnel syndrome. In contrast, conventional T2W-MRI revealed high signal intensity in eight elbows and low signal intensity in three elbows. Three elbows with low signal MRI showed normal nerve conduction velocity of the ulnar nerve. Diffusion-weighted MRI appears to be an attractive technique for diagnosis of cubital tunnel syndrome in its early stages which show normal electrophysiological and conventional MRI studies.

Prediction of motor function by diffusion tensor tractography in patients with basal ganglion haemorrhage

INTRODUCTION

Haemorrhagic stroke is one of the leading causes of death and the most common cause of long-term adult disability. An accurate estimation of prognosis is very important for haemorrhagic stroke patients. Impairment of motor function caused by pyramidal tract injury is common in these patients. In this study, we performed MR diffusion tensor tractography (DTT) to predict the impairment of motor function in patients with basal ganglion haemorrhage and explore its clinical value.

MATERIAL AND METHODS

Diffusion tensor tractography was performed in 33 patients with basal ganglia haemorrhage within 2 weeks after onset to visualize the course of pyramidal tracts (PTs), and patients were classified into four groups according to the fibre ratio of PTs, calculated by dividing the PT number of the affected hemisphere by that of the unaffected hemisphere, as follows: type A, the fibre ratio was less than 1/4; type B, less than 1/2; type C, more than 1/2; and type D, more than 3/4. The upper extremity motricity index (UMI) was used to evaluate the motor function at onset and 6 months after onset. Upper extremity motricity index scores were compared among the different groups and a Spearman analysis was performed to correlate the UMI scores with different integrity of pyramidal tracts.

RESULTS

There were no differences in the UMI scores at onset among the 4 groups (p< 0.05). The UMI scores obtained at 6 months after onset were significantly unequal and were influenced by the DTT type (p < 0.05). There was a significant correlation between the integrity of the pyramidal tracts and the UMI scores 6 months after onset (r = 0.7312, p< 0.05).

CONCLUSIONS

There was a positive correlation between the integrity grade of pyramidal tracts and the motor function, showing that the more seriously were the pyramidal tracts damaged, the worse was the motor function. The DTT findings of the pyramidal tract in acute cerebral haemorrhage may valuably predict the motor function outcome.

A case of tacrolimus-induced encephalopathy after kidney transplantation

We present a case of tacrolimus-induced encephalopathy after successful kidney transplantation. An 11-year-old girl presented with sudden onset of neurologic symptoms, hypertension, and psychiatric symptoms, with normal kidney function, after kidney transplantation. The symptoms improved after cessation of tacrolimus. Magnetic resonance imaging (MRI) showed acute infarction of the middle cerebral artery (MCA) territory in the right frontal lobe. Three days later, she had normal mental function and maintained normal blood pressure with left hemiparesis. Follow-up MRI was performed on D19, showing new infarct lesions at both cerebral hemispheres. Ten days later, MRI showed further improvement, but brain single photon emission computed tomography (SPECT) showed mild reduction of uptake in both the anterior cingulate gyrus and the left thalamus. One month after onset of symptoms, angiography showed complete resolution of stenosis. However, presenting as a mild fine motor disability of both hands and mild dysarthria, what had been atrophy at both centrum semiovale at 4 months now showed progression to encephalomalacia. There are two points of interest in this case. First, encephalopathy occurred after administration of tacrolimus and improved after discontinuation of the drug. Second, the development of right-side hemiplegia could not be explained by conventional MRI; but through diffusion tensor imaging (DTI) and diffusion tensor tractography (DTT) of white matter tract, visualization was possible.

Relationships between brain tumor and optic tract or calcarine fissure are involved in visual field deficits after surgery for brain tumor

PURPOSE

Diffusion tensor tractography provides useful information regarding the surgical strategy for brain tumors. The goal of the present study was to analyze relationships between visual field deficits and the locations of brain tumors compared with optic tracts as visualized by tractography, and compared with the calcarine fissure.

METHODS

Subjects comprised 11 patients with brain tumor in the occipital lobe or atrium of the lateral ventricle who underwent surgery between October 2006 and February 2009. Tumors were categorized as Type A, with almost all the optic tract in the occipital lobe or atrium of the lateral ventricle running close to and stretched by the brain tumor; and Type B, with the optic tract running at least partially distant to the brain tumor and remaining unstretched.

RESULTS

Those type A optic tracts that were laterally compressed by brain tumors (Cases 1-3) displayed hemianopsia after surgery. When the brain tumor was located rostro-medial to the calcarine fissure and optic tracts were compressed caudally by the tumor, lower quadrant hemianopsia remained after surgery (Cases 4, 5). In other cases, the visual field remained or improved to normal after surgery.

CONCLUSION

The relationship between optic tracts or the calcarine fissure, and brain tumors in the occipital lobe or atrium of the lateral ventricle is related to visual field deficits after surgery. In particular, those Type A optic tracts that are compressed laterally show hemianopsia of the visual field after surgery.

Diffusion tensor imaging and tractography of the median nerve in carpal tunnel syndrome: preliminary results

The purpose was to demonstrate the feasibility of in vivo diffusion tensor imaging (DTI) and tractography of the human median nerve with a 1.5-T MR scanner and to assess potential differences in diffusion between healthy volunteers and patients suffering from carpal tunnel syndrome. The median nerve was examined in 13 patients and 13 healthy volunteers with MR DTI and tractography using a 1.5-T MRI scanner with a dedicated wrist coil. T1-weighted images were performed for anatomical correlation. Mean fractional anisotropy (FA) and mean apparent diffusion coefficient (ADC) values were quantified in the median nerve on tractography images. In all subjects, the nerve orientation and course could be detected with tractography. Mean FA values were significantly lower in patients (p=0.03). However, no statistically significant differences were found for mean ADC values. In vivo assessment of the median nerve in the carpal tunnel using DTI with tractography on a 1.5-T MRI scanner is possible. Microstructural parameters can be easily obtained from tractography images. A significant decrease of mean FA values was found in patients suffering from chronic compression of the median nerve. Further investigations are necessary to determine if mean FA values may be correlated with the severity of nerve entrapment.

Diffusion tensor tractography predicts motor functional outcome in patients with spontaneous intracerebral hemorrhage

OBJECTIVE

We prospectively investigated the predictive value of diffusion tensor tractography for motor functional outcome in a case series of patients with intracerebral hemorrhage.

METHODS

Diffusion tensor tractography was performed in 17 patients with intracerebral hemorrhage (putamen, nine patients; thalamus, seven patients; combined, one patient) within 5 days after onset. Mean fractional anisotropy (FA) and apparent diffusion coefficient (ADC) values along the corticospinal tracts at the level of the hematoma were measured bilaterally, and the ratios of values (hematoma side/contralateral side) were determined as FA and ADC ratios, respectively. Patients were evaluated for motor function on admission and at 3 months after onset using the manual muscle test score and then divided into good (manual muscle test, 4-5) and poor (manual muscle test, 0-3) motor function groups.

RESULTS

FA ratio measured shortly after the onset of intracerebral hemorrhage correlated well with motor functional outcome at 3 months (P < 0.05) but not with motor function on admission. FA ratios in the group with good motor functional outcome were significantly higher than those in the group with poor motor functional outcome (P < 0.01). The ADC ratio did not correlate with motor function either on admission or at 3 months. All patients with an FA ratio greater than 0.8 had a good motor functional outcome. In three patients, however, motor functional outcomes were favorable even though FA ratios were not high; in these patients, ADC ratios tended to be elevated.

CONCLUSION

Motor functional outcome in patients with intracerebral hemorrhage can be predicted by measuring FA values using diffusion tensor tractography.

Motor control via spared peri-infarct corticospinal tract in patients with pontine infarct

We investigated the motor control pathway in 3 patients with pontine infarct using diffusion tensor tractography and functional magnetic resonance imaging. The motor tracts of the affected hemisphere were observed to pass along the same spared peri-infarct corticospinal tract area of the pons on both the first and second diffusion tensor tractography. It seems that the main motor function of these patients is controlled via the spared peri-infarct corticospinal tract.

Fractional anisotropy correlates with auditory simple reaction time performance

During the last two decades, modern imaging studies focused intensively on the broad field of reaction time paradigms and significantly enhanced the understanding of behavioral performance. However, interindividual variations of simple reaction time (SRT) have been barely investigated. In this study, we intended to identify neural correlates of interindividual variation in auditory SRT (aSRT) employing the Poffenberger paradigm with auditory stimuli, in order to investigate neural processing speed performance. We conducted a whole-head voxel based morphometry analysis of fractional anisotropy (FA) in 19 healthy, right handed subjects. Simple regression analysis between FA and interindividual aSRT measures was performed for each voxel. Significant positive correlation (R(2): 0.44/0.78 min/max) for FA vs. individual mean aSRT was found in the right central cerebellum dorso-cranial of the dentate nucleus. A significant correlation (R(2): 0.453/0.633 min/max) was also detected between FA and the hand performance index, which characterizes the intraindividual RT difference between left and right hand, within the precentral portion of the pyramidal tract in the left hemisphere. Fast right handed response correlated with high local FA values located within neural structures participating in right hand control. Against the background of only right handed participants in our study, the hypothesis of local myelination as one basic condition influencing reaction time performance is strongly supported. The presented results identify brain areas involved in the processing speed of the aSRT tasks. We propose that the presented findings are due to an influence of participants' right hand preference on both FA and aSRT measures.

Motor outcome according to the integrity of the corticospinal tract determined by diffusion tensor tractography in the early stage of corona radiata infarct

Diffusion tensor tractography (DTT) is useful for exploring the state of the corticospinal tract (CST). An accurate estimation of the integrity of the CST in the early stage of a cerebral infarct would enable a determination of motor recovery. DTT was performed to classify CST integrity following a corona radiata infarct to evaluate if the procedure could characterize the motor outcome of the affected hand. Fifty-five patients with completely paralyzed hands due to a corona radiata infarct were recruited for the study, and DTT images were obtained within 7-30 days after a stroke. The DTI findings for the patients were classified into four groups. In type A, the CST was preserved around the infarct; in type B, the CST originated from a cortex other than the primary motor cortex; in type C, the CST was interrupted at the infarct; in type D, the CST failed to reach the infarct due to degeneration. Six months after a stroke, the motor function of the affected hand was evaluated with the motricity index (MI) for the hand, the Medical Research Council score (MRC) for finger extensors and the modified Brunnstrom classification (MBC). These indices were significantly influenced by the DTT type (p<0.05). The highest MI, MRC and MBC were seen in the DTT type A patients; the lowest MI, MRC and MBC were seen in the DTT type D patients (p<0.05). The integrity of the corticospinal tract determined by DTT obtained during the early stage of a corona radiata infarct seems to be helpful in predicting the motor outcome of the affected hand.

Motor outcome according to diffusion tensor tractography findings in the early stage of intracerebral hemorrhage

We tried to investigate the motor outcome according to diffusion tensor tractography (DTT) findings for the corticospinal tract (CST) in the early stage for hemiparetic patients with intracerebral hemorrhage (ICH). Forty patients with severe paralysis of the affected side were enrolled. DTT was obtained in the early stage of the stroke (7-30 days) and was classified into four groups: type A, the CST originating from primary motor cortex was preserved around the hematoma; type B, the CST was similar to type A except the fiber originated from the adjacent areas to the primary motor cortex; type C, the CST was interrupted at or around the hematoma; and type D, the CST did not reach the hematoma due to degeneration (Fig. 1). Six months after onset, motor function was measured and the statistical influence of the DTT type was tested. Initially, none of the motor function scales of the affected side differed among the four DTT types. Six months after the onset of ICH, motor functions of the same side were significantly different according to DTT type (p<0.05). All motor scales were highest in the DTT type A group, and were lowest in the DTT type D group (p<0.0003). The early DTT findings for CST may be used to predict the motor outcome of the affected extremities in hemiparetic patients with ICH.

Diffusion tensor imaging demonstrates focal lesions of the corticospinal tract in hemiparetic patients with cerebral palsy

The purpose of this study was to use diffusion tensor imaging (DTI) with fiber tractography (FT) to demonstrate focal lesions of the corticospinal tract (CST) in hemiparetic patients with cerebral palsy (CP) who showed no specific focal lesions on conventional brain MRI. Four hemiparetic patients with CP (three left hemiparesis, mean age: 2.5 years, range: 0.9-7.0) and four age-matched controls were recruited. DTI was performed using a 1.5-T system with a synergy-L Sensitivity Encoding head coil. Fractional anisotropy (FA) and apparent diffusion coefficients (ADC) were measured using the region of interest (ROI) method. We estimated the asymmetric anisotropy index (AA) and asymmetric mean diffusivity index (AD) to evaluate the asymmetry between right and left CSTs. All four patients showed interrupted FT at the affected periventricular white matter (PVWM) level compared to that of the opposite side; this was not detected on conventional brain MRI and explained the hemiparesis of these patients. Compared to the data of controls, all patients showed significant AA and AD only at the PVWM level. DTI with FT demonstrated focal lesions at the PVWM level. We conclude that DTI with FT may be a useful modality for investigating focal lesions in hemiparetic patients with CP.

[Useful imaging of the ear]

Good anatomical knowledge is necessary to make an effective diagnosis in ear pathology. The purpose of this article is to summarize the main landmarks of the ear. Anatomic definitions of the external ear, middle ear, and bony labyrinth are described on routine spiral CT, and the anatomic definition of the membranous labyrinth and the cochleovestibular nerve on MRI is reviewed.

Quantitative analysis along the pyramidal tract by length-normalized parameterization based on diffusion tensor tractography: application to patients with relapsing neuromyelitis optica

In this study, we introduced a length-normalized parameterization method to establish anatomical correspondence of white matter fiber tracts across subjects and applied this method to investigate the presence of abnormal diffusion along the pyramidal tract (PYT) of relapsing neuromyelitis optica (RNMO) patients without visible brain lesions. In this approach, the part of the PYT between the lowest slice of the cerebral peduncle and the uppermost slice of the lateral ventricle was reconstructed to establish the anatomical correspondence across subjects using diffusion tensor tractography. Then it was parameterized by normalizing its length and dividing equally the normalized length into a certain number of segments, so that the comparability of each segment across subjects along the PYT was established. Tract-specific diffusion indices, including directionally averaged diffusivity (D(av)), fractional anisotropy (FA), primary diffusivity (lambda(1)) and transverse diffusivity (lambda(23)), were obtained from each segment. Thus, the distribution maps of these indices along the PYT were obtained. The distribution maps of D(av), FA, and lambda(23) of RNMO patients were significantly different from those of healthy controls, especially in the lower part of the PYT. The differences may be caused by secondary degeneration to lesions in the spinal cord. In conclusion, a length-normalized parameterization method is proposed to establish anatomical correspondence for the PYT. Compared with existed methods, a major merit of our method is to provide comparability across subjects along the PYT on the basis of diffusion tensor tractography and to make it possible for the quantitative analysis along the fiber tract. This method can also be used to quantitatively analyze other white matter fiber tracts between two definite anatomic landmarks in many neurological or psychiatric diseases.