Diffusion anisotropy measurement of brain white matter is affected by voxel size: underestimation occurs in areas with crossing fibers

BACKGROUND AND PURPOSE

Voxel size/shape of diffusion tensor imaging (DTI) may directly affect the measurement of fractional anisotropy (FA) in regions where there are crossing fibers. The purpose of this article was to investigate the effect of voxel size/shape on measured FA by using isotropic and nonisotropic voxels.

MATERIALS AND METHODS

Ten healthy adult volunteers had MR imaging by using a 1.5 T clinical imager. DTI was performed with 2 different voxel sizes: a 2-mm-section isotropic voxel (2 x 2 x 2 mm(3)) and a 6-mm-section nonisotropic voxel (2 x 2 x 6 mm(3)). Images were obtained by using a single-shot echo-planar imaging technique with motion-probing gradients in 15 orientations and a b-value of 1000 s/mm(2). FA and the apparent diffusion coefficient (ADC) were measured at different sites of the brain.

RESULTS

When smaller isotropic voxels were used, the FA was greater in areas with crossing fibers, including the superior longitudinal fasciculus, the thalamus, and the red nucleus; the FA was not significantly different in areas without crossing fibers, such as the corpus callosum, the posterior limb of the internal capsule, and the corticospinal tract at the level of the centrum semiovale (P>.05). The ADC values were not affected by voxel size/shape at any of the areas of the brain that were measured.

CONCLUSION

FA values that are measured in regions containing crossing fibers are underestimated when using nonisotropic DTI.

MR tractography for the evaluation of functional recovery from lenticulostriate infarcts

OBJECTIVE

To evaluate the anatomic and clinical relationship between the lenticulostriate artery (LSA) territory and the corticospinal tract (CST) in patients with acute infarcts in this territory using MR tractography.

METHODS

Thirteen consecutive patients who presented with acute infarcts in the LSA territory and who also had undergone an MRI study within 3 days after symptom onset were studied. Visualization of the CST was achieved by postprocessing the acquired diffusion tensor imaging data. To classify lesion location, the LSA territory was divided into four subsegments, the boundaries of which were drawn by axial and coronal planes crossing through the foramen of Monro. Infarct volume and extent of CST involvement were measured and compared with neurologic findings.

RESULTS

All of the infarcts were located in the posterior segment. All of the depicted CSTs crossed the LSA territory only at the posterosuperior quadrant. The extent of CST involvement within the infarcts was correlated with the severity of the patient's motor deficit (p < 0.01) and with the clinical outcome (p < 0.05).

CONCLUSIONS

The corticospinal tracts (CSTs) crossed the lenticulostriate artery territory exclusively at the posterosuperior quadrant, and the degree of CST involvement within the infarcts was directly related to stroke severity and functional recovery.

Posterior cingulate metabolic changes in frontotemporal lobar degeneration detected by magnetic resonance spectroscopy

Differences in prognosis and symptomatic treatment have highlighted the importance of the differential diagnosis of frontotemporal lobar degeneration (FTLD) and other dementias, but the variable clinical features make diagnosis difficult. We studied metabolic changes using multivoxel proton magnetic resonance spectroscopy (MRS) in regions of FTLD, including the posterior cingulate gyrus, which is also the area most affected by Alzheimer's disease (AD) in the early stages. We examined six patients with FTLD, six with presumed AD, and five healthy volunteers using repetition and echo times of 2000 and 135 ms. We analysed peak ratios of choline (Cho), creatine (Cr), and N-acetylaspartate (NAA) from frontal and temporoparietal regions, basal ganglia, and posterior cingulate gyrus in both hemispheres. A decreased NAA/Cr ratio was observed in the posterior cingulate gyri in presumed AD (right: 1.56+/-0.44, P =0.011; left: 1.46+/-0.25, P =0.008) and FTD (right: 1.47+/-0.40, P =0.005; left: 1.36+/-0.32, P =0.002). No statistically significant changes in Cho/Cr were identified in the posterior cingulate gyri in presumed AD or FTLD, and no differences were observed in peak ratios in other regions. Decreased NAA may reflect neuronal activity in the posterior cingulate gyrus, and this study may contribute to insights into the pathophysiology of FTLD.

Secondary aneurysmal bone cyst derived from a giant-cell tumour of the skull base

We report a 20-year-old man with a giant-cell tumour of the skull base which showed multiple fluid levels on MRI.

Wallerian degeneration of the inferior cerebellar peduncle depicted by diffusion weighted imaging

Wallerian degeneration of the inferior cerebellar peduncle has never been demonstrated on imaging studies. We describe a case in which it was depicted by thin slice diffusion weighted imaging. Location to the inferior cerebellar peduncle was confirmed by a fibre tracking method.

Proton chemical shift imaging in normal pressure hydrocephalus

BACKGROUND AND PURPOSE

Differentiation of normal pressure hydrocephalus (NPH) from other types of dementia and the selection of appropriate candidates for shunt surgery remain a clinical challenge. The aims of this study were to assess the efficacy of cerebral metabolites depicted by proton chemical shift imaging (1H-CSI) in distinguishing NPH from other dementias and to examine the relationship between metabolite changes and the outcome of shunt surgery.

METHODS

1H-CSI measurements were obtained in nine patients with clinical diagnosis of NPH; six patients with other types of dementia, including Alzheimer and Pick disease; and five control subjects. The 1H-CSI sequence consisted of a double spin-echo sequence with imaging parameters of 2000/135/4-2 (TR/TE/acquisitions). Volumes of interest were selected from a section through the lateral ventricles. The peak areas and ratios of N-acetylaspartate, creatine, choline, and lactate were calculated. In two patients, follow-up 1H-CSI and N-isopropyl (123I)-p-iodoamphetamine brain perfusion imaging were available after treatment with continuous spinal drainage.

RESULTS

Lactate peaks were observed in the lateral ventricles for all patients with NPH (lactate/creatine, 0.23 +/- 0.14) but not for patients with other types of dementia or control subjects. In all cases, we noted no significant differences in the peak ratios in the voxels located at the white matter near the lateral ventricles. In one patient with NPH, intraventricular lactate disappeared and regional CBF recovered after drainage.

CONCLUSION

The intraventricular lactate level may be useful in differentiating NPH from other types of dementia.

Angiomyolipoma arising in the thigh

A 41-year-old man presented with an asymptomatic mass in the right medial thigh. Magnetic resonance imaging (MRI) revealed a well-demarcated, 10-cm mass in the right adductor muscles. The margins of the mass exhibited high signal intensity and the rest showed low or iso signal intensity on T1-weighted MR images. However, the high signal intensity was decreased on T2-weighted images with fat suppression. The central part of the tumor was of inhomogeneous high signal intensity on T2-weighted images; after Gd-DTPA injection it enhanced in homogeneously on T1-weighted images with fat suppression. On dynamic computed tomography (CT) in the arterial phase, there were strongly enhancing spotty areas in the tumor. At surgery, a yellow-whitish tumor was resected and a pathological diagnosis of angiomyolipoma (AML) in the thigh was made.

Application of proton chemical shift imaging in monitoring of gamma knife radiosurgery on brain tumors

Our objective was to assess proton chemical shift imaging for potential clinical application in monitoring response to gamma knife radiosurgery. Twenty-five proton chemical shift imaging studies and conventional magnetic resonance images were performed on six patients with intracranial tumors. The peak areas of N-acetylaspartate, choline-containing compounds (Cho), creatine, and lipids were calculated and normalized to N-acetylaspartate in the contralateral hemisphere. The spectra from the lesion before treatment showed a relatively high Cho peak, reported as a characteristic spectrum of tumors. Tumor size and Cho level after radiosurgery did not increase except in two cases. In these cases, radiation necrosis was observed with elevated Cho and a mobile lipid peak. Stable or decreased Cho seems to suggest a loss of tumor viability, and changes in Cho indicate the effectiveness of radiosurgery. Increasing Cho and the appearance of the mobile lipid peak may distinguish radiation necrosis from recurrent tumors, which cannot be distinguished by magnetic resonance imaging.

Neurovascular compression of the rostral ventrolateral medulla related to essential hypertension

The rostral ventrolateral medulla (RVLM) is thought to serve as a final common pathway for the integration of central cardiovascular information and to be important for the mediation of central pressor responses. An association between essential hypertension and neurovascular compression of the RVLM has been reported. To confirm this relationship and to quantitatively measure the distances between the RVLM and the neighboring arteries, we performed magnetic resonance imaging using a high-resolution 512x512 matrix and magnetic resonance angiography in 49 subjects (21 patients with essential hypertension, 10 patients with secondary hypertension, and 18 normotensive subjects). One patient with essential hypertension was excluded from the evaluations because of inadequate assessment due to poor images. Neurovascular compression of the RVLM was observed in 15 of 20 (75%) patients with essential hypertension. In contrast, neurovascular compression was observed in only 1 of 10 (10%) patients with secondary hypertension and only 2 of 18 (11%) normotensive subjects. The rate of observed neurovascular compression in the essential hypertension group was significantly higher than that in the secondary hypertension group and the normotensive group (P<.01 for both). The distances between the RVLM and the nearest arteries in the essential hypertension group were significantly shorter than those in the other groups (P<.05 for all). On the other hand, the distances between the surface of the medulla oblongata and the nearest arteries did not differ among these three groups. These results suggest that neurovascular compression of the RVLM, but not of the other regions of the medulla oblongata, is particularly related to essential hypertension.

[Trial of radiation and cisplatin, carboplatin combination chemotherapy for advanced cancer (W-platinum chemoradiotherapy]

Cisplatin was reported to be an effective radiation sensitizing agent. The effect was also reported to depend on dose intensity. But the incidence of complication was demonstrated in the relationship with the dose escalation curve of anti-cancer agent. The major side effect of CDDP was occasionally serious, as in renal toxicity or bone marrow suppression. W-Platinum is the trial of concurrent chemoradiotherapy. Cisplatin and its derivative, Carboplatin, were selected as effective radiation sensitizing agents and to obtain high-dose intensity and additive cytotoxicities by interaction between the two drugs. Concomitant administration of two platinum anti-cancer agents has the advantage of reduction of side effects compared with administration of single anti-cancer agents to the same degree. The first case was a recurrence of epipharyngeal cancer after 3 courses of chemotherapy, including CDDP or CBDCA. This case was suspected to be cancer-resistant to CDDP. The second case was post-operative residual lung cancer. The pre-operative diagnosis was stage III A. A poor prognosis was expected. This case was disease-free and alive for 1 year after W-Platinum administration. The most frequent complication was bone marrow suppression. Patients were rescued from bone marrow suppression with administration of G-CSF. Renal toxicity could be suppressed with sufficient hydration.

Flow velocity of the cortical vein and its effect on functional brain MRI at 1.5T: preliminary results by cine-MR venography

The purpose of this study is to demonstrate the effect of altering flow velocity of cerebral cortical veins as the source of the signal change observed in functional magnetic resonance imaging (fMRI) of the brain. 10 healthy volunteers were examined after instructions in self-paced hand grasping. Experiments were performed using a 1.5-Tesla whole body MR scanner with a conventional two-dimensional gradient echo sequence (TR/TE/flip angle 400/60/40, first order flow rephased, reduced band width 8 Hz/pixel). Flow velocity measurements were performed for the cortical veins which corresponded to the activated areas depicted on fMRI. Velocity was estimated from the cine-MR venography (cine-MRV) with a tagging technique. Flow phantom studies were performed to delineate the effect of flow velocity differences upon the subtraction images of fMRI. The cine-MRV revealed increased flow velocity of the cortical veins during activation in seven volunteers, with a mean velocity difference of 15 mm/sec. Flow phantom studies suggested that the increased flow velocity may result in changes of the flow signal profile due to oblique flow displacement. Subtraction of the two images with different flow profiles produces flow signal enhancement. Increased flow velocity of the cortical veins during the activation is an important factor which contributes to the signal of fMRI.

Evaluation of metabolic heterogeneity in brain tumors using 1H-chemical shift imaging method

Seventeen brain tumors were measured by 1H-CSI (chemical shift imaging) in a 1.5 T clinical magnetic resonance scanner. The metabolic peaks obtained were evaluated by two methods. One method was to obtain the percentage of each metabolite relative to the combined choline, creatine and NAA peak areas, and the other method was to obtain a ratio of the tumor to contralateral brain. The percentage of choline (%Cho) and choline ratio increased, and the %NAA and NAA ratio decreased in the gliomas and malignant tumors. In relation to grading, %Cho increased but the choline ratio did not. We believed the reason for this was that there were many foci of microscopic necrosis in the glioma grade IV. Free lipids were observed in most of the high grade gliomas and in a malignant tumor. Lactate increased in higher grade tumors. Meningiomas showed the highest %Cho. Statistical differences between the grades of glioma were not detected because many tumors had heterogeneous tissue. One resolution to this problem was metabolite mapping. Mapping of the percentage of metabolites was suitable because it described the regional metabolic changes and the resulting signal to noise ratio was better than that achieved by other methods of evaluation.

[The role of magnetic resonance spectroscopic imaging in patients with Parkinson's disease]

There are some single voxel proton magnetic resonance spectroscopy(MRS) of Parkinson's disease but no multi-voxel proton MRS. Proton magnetic resonance spectroscopic imaging(MRSI) is the multi-voxel method, from which we can obtain many spectra from many voxel at the same time. The distribution of each metabolite can be observed in the metabolite map. Although defects in oxidative phosphorylation have been reported from the studies of Parkinson's disease and dopaminergic cell death has been observed, the cause of Parkinson's disease is unknown. The spectra from the striatum and surroundings and the metabolite maps in MRSI will help to understand the pathogenesis of the disease.

[A case of superior vena cava syndrome treated with combination radiation and CRE (CBDCA and VP-16) therapy]

Carboplatin and etoposide were reported to be excellent radiation sensitizers. We encountered a patient with SVC syndrome due to lung cancer who was successfully treated by combination carboplatin, etoposide and hyperfractionation radiotherapy. A 72-year-old man was admitted to our hospital because of remarkable face edema. Computed tomography revealed a huge lung tumor and compressed SVC due to tumor growth. Acute tumor regression was essential for this case. We performed combination chemotherapy and radiation. The regime consisted of CBDCA 300 mg (day 1 1 hr drip infusion) and etoposide 50 mg/day for 21 days by oral administration. Two daily fractionations of 1.4 Gy were delivered 5 days-a-week, with a 4 h interval between fractions (total dose 49.8 Gy). Complete response of huge tumor was attained in this case. The major side effect associated with the therapy was myelosuppression. The patient's quality of life has been remarkably improved with this therapy.