Transcranial MR Imaging-Guided Focused Ultrasound Interventions Using Deep Learning Synthesized CT.

BACKGROUND AND PURPOSE: Transcranial MR imaging-guided focused ultrasound is a promising novel technique to treat multiple disorders and diseases. Planning for transcranial MR imaging-guided focused ultrasound requires both a CT scan for skull density estimation and treatment-planning simulation and an MR imaging for target identification. It is desirable to simplify the clinical workflow of transcranial MR imaging-guided focused ultrasound treatment planning. The purpose of this study was to examine the feasibility of deep learning techniques to convert MR imaging ultrashort TE images directly to synthetic CT of the skull images for use in transcranial MR imaging-guided focused ultrasound treatment planning. MATERIALS AND METHODS: The U-Net neural network was trained and tested on data obtained from 41 subjects (mean age, 66.4 ± 11.0 years; 15 women). The derived neural network model was evaluated using a k-fold cross-validation method. Derived acoustic properties were verified by comparing the whole skull-density ratio from deep learning synthesized CT of the skull with the reference CT of the skull. In addition, acoustic and temperature simulations were performed using the deep learning CT to predict the target temperature rise during transcranial MR imaging-guided focused ultrasound. RESULTS: The derived deep learning model generates synthetic CT of the skull images that are highly comparable with the true CT of the skull images. Their intensities in Hounsfield units have a spatial correlation coefficient of 0.80 ± 0.08, a mean absolute error of 104.57 ± 21.33 HU, and a subject-wise correlation coefficient of 0.91. Furthermore, deep learning CT of the skull is reliable in the skull-density ratio estimation (r = 0.96). A simulation study showed that both the peak target temperatures and temperature distribution from deep learning CT are comparable with those of the reference CT. CONCLUSIONS: The deep learning method can be used to simplify workflow associated with transcranial MR imaging-guided focused ultrasound.

Angle-corrected imaging transcranial doppler sonography versus imaging and nonimaging transcranial doppler sonography in children with sickle cell disease.

BACKGROUND AND PURPOSE: Nonimaging transcranial Doppler sonography (TCD) and imaging TCD (TCDI) are used for determination of the risk of stroke in children with sickle cell disease (SCD). The purpose was to compare angle-corrected, uncorrected TCDI, and TCD blood flow velocities in children with SCD. MATERIALS AND METHODS: A total of 37 children (mean age, 7.8 +/- 3.0 years) without intracranial arterial narrowing determined with MR angiography, were studied with use of TCD and TCDI at the same session. Depth of insonation and TCDI mean velocities with and without correction for the angle of insonation in the terminal internal carotid artery (ICA) and middle (MCA), anterior (ACA), and posterior (PCA) cerebral arteries were compared with TCD velocities with use of a paired t test. RESULTS: Two arteries were not found on TCDI compared with 15 not found on TCD. Average angle of insonation in the MCA, ACA, ICA, and PCA was 31 degrees , 44 degrees , 25 degrees , and 29 degrees , respectively. TCDI and TCD mean depth of insonation for all arteries did not differ significantly; however, individual differences varied substantially. TCDI velocities were significantly lower than TCD velocities, respectively, for the right and left sides (mean +/- SD): MCA, 106 +/- 22 cm/s and 111 +/- 33 cm/s versus 130 +/- 19 cm/s and 134 +/- 26 cm/s; ICA, 90 +/- 14 cm/s and 98 +/- 27 cm/s versus 117 +/- 18 cm/s and 119 +/- 23 cm/s; ACA, 74 +/- 24 cm/s and 88 +/- 25 cm/s versus 105 +/- 23 cm/s and 105 +/- 31 cm/s; and PCA, 84 +/- 27 cm/s and 82 +/- 21 cm/s versus 95 +/- 23 cm/s and 94 +/- 20 cm/s. TCD and angle-corrected TCDI velocities were not statistically different except for higher angle-corrected TCDI values in the left ACA and right PCA. CONCLUSION: TCD velocities are significantly higher than TCDI velocities but are not different from the angle-corrected TCDI velocities. TCDI identifies the major intracranial arteries more effectively than TCD.

Arterial spin-labeling and MR spectroscopy in the differentiation of gliomas.

BACKGROUND AND PURPOSE: Noninvasive grading of gliomas remains a challenge despite its important role in the prognosis and management of patients with intracranial neoplasms. In this study, we evaluated the ability of cerebral blood flow (CBF)-guided voxel-by-voxel analysis of multivoxel proton MR spectroscopic imaging ((1)H-MRSI) to differentiate low-grade from high-grade gliomas. MATERIALS AND METHODS: A total of 35 patients with primary gliomas (22 high grade and 13 low grade) underwent continuous arterial spin-labeling perfusion-weighted imaging (PWI) and (1)H-MRSI. Different regions of the gliomas were categorized as "hypoperfused," "isoperfused," and "hyperperfused" on the basis of the average CBF obtained from contralateral healthy white matter. (1)H-MRSI indices were computed from these regions and compared between low- and high-grade gliomas. Using a similar approach, we applied a subgroup analysis to differentiate low- from high-grade oligodendrogliomas because they show different physiologic and genetic characteristics. RESULTS: Cho(glioma (G)/white matter (WM)), Glx(G/WM), and Lip+Lac(G)/Cr(WM) were significantly higher in the "hyperperfused" regions of high-grade gliomas compared with low-grade gliomas. Cho(G/WM) and Lip+Lac(G)/Cr(WM) were also significantly higher in the "hyperperfused" regions of high-grade oligodendrogliomas. However, metabolite ratios from the "hypoperfused" or "isoperfused" regions did not exhibit any significant differences between high-grade and low-grade gliomas. CONCLUSION: The results suggest that (1)H-MRSI indices from the "hyperperfused" regions of gliomas, on the basis of PWI, may be helpful in distinguishing high-grade from low-grade gliomas including oligodendrogliomas.

Intracranial Applications of MR Imaging-Guided Focused Ultrasound.

Initially used in the treatment of prostate cancer and uterine fibroids, the role of focused ultrasound has expanded as transcranial acoustic wave distortion and other limitations have been overcome. Its utility relies on focal energy deposition via acoustic wave propagation. The duty cycle and intensity of focused ultrasound influence the rate of energy deposition and result in unique physiologic and biomechanical effects. Thermal ablation via high-intensity continuous exposure generates coagulative necrosis of tissues. High-intensity, pulsed application reduces temporally averaged energy deposition, resulting in mechanical effects, including reversible, localized BBB disruption, which enhances neurotherapeutic agent delivery. While the precise mechanisms remain unclear, low-intensity, pulsed exposures can influence neuronal activity with preservation of cytoarchitecture. Its noninvasive nature, high-resolution, radiation-free features allow focused ultrasound to compare favorably with other modalities. We discuss the physical characteristics of focused ultrasound devices, the biophysical mechanisms at the tissue level, and current and emerging applications.

Synthetic MRI for Clinical Neuroimaging: Results of the Magnetic Resonance Image Compilation (MAGiC) Prospective, Multicenter, Multireader Trial.

BACKGROUND AND PURPOSE: Synthetic MR imaging enables reconstruction of various image contrasts from 1 scan, reducing scan times and potentially providing novel information. This study is the first large, prospective comparison of synthetic-versus-conventional MR imaging for routine neuroimaging. MATERIALS AND METHODS: A prospective multireader, multicase noninferiority trial of 1526 images read by 7 blinded neuroradiologists was performed with prospectively acquired synthetic and conventional brain MR imaging case-control pairs from 109 subjects (mean, 53.0 ± 18.5 years of age; range, 19-89 years of age) with neuroimaging indications. Each case included conventional T1- and T2-weighted, T1 and T2 FLAIR, and STIR and/or proton density and synthetic reconstructions from multiple-dynamic multiple-echo imaging. Images were randomized and independently assessed for diagnostic quality, morphologic legibility, radiologic findings indicative of diagnosis, and artifacts. RESULTS: Clinical MR imaging studies revealed 46 healthy and 63 pathologic cases. Overall diagnostic quality of synthetic MR images was noninferior to conventional imaging on a 5-level Likert scale (P < .001; mean synthetic-conventional, -0.335 ± 0.352; Δ = 0.5; lower limit of the 95% CI, -0.402). Legibility of synthetic and conventional morphology agreed in >95%, except in the posterior limb of the internal capsule for T1, T1 FLAIR, and proton-density views (all, >80%). Synthetic T2 FLAIR had more pronounced artifacts, including +24.1% of cases with flow artifacts and +17.6% cases with white noise artifacts. CONCLUSIONS: Overall synthetic MR imaging quality was similar to that of conventional proton-density, STIR, and T1- and T2-weighted contrast views across neurologic conditions. While artifacts were more common in synthetic T2 FLAIR, these were readily recognizable and did not mimic pathology but could necessitate additional conventional T2 FLAIR to confirm the diagnosis.

Diffusion tensor imaging in amyotrophic lateral sclerosis: volumetric analysis of the corticospinal tract.

BACKGROUND AND PURPOSE: Diffusion tensor imaging (DTI) allows direct visualization and volumetric analysis of the corticospinal tract (CST). The purpose of this study was to determine whether color maps and fiber tracking derived from DTI data are valuable in detecting and quantifying CST degeneration in patients with amyotrophic lateral sclerosis (ALS). METHODS: Sixteen patients with ALS with clinical signs of upper motor neuron (UMN) involvement and 17 healthy subjects were studied with the use of DTI. Disease severity was determined by means of the ALS Functional Rating Scale-Revised (ALSFRS-R) and an UMN involvement score. DTI was acquired with a 12-direction, single-shot, spin-echo echo-planar sequence. The CST from the lower pons to the corona radiata at the level of the corpus callosum on 4 contiguous coronal sections was manually segmented by using color maps generated from the DTI data. The left and right CST volumes were measured separately and normalized to the total intracranial volume. Normalized CST volumes were compared between patients with ALS and healthy subjects. RESULTS: The CST volumes of patients with ALS were significantly reduced (P < .01, unpaired t test) compared with healthy subjects, in both affected and nonaffected hemispheres. No significant correlation was found between CST volumes and any of the clinical parameters, including disease duration, ALSFRS-R, or UMN involvement score. CONCLUSION: This study shows that volumetric analysis by using DTI-based color maps is valuable in detecting and monitoring structural degeneration of the CST. This will lead to objective and quantitative assessment of axonal degeneration in ALS.

A prospective longitudinal brain morphometry study of children with sickle cell disease.

BACKGROUND AND PURPOSE: Age-related changes in brain morphology are crucial to understanding the neurobiology of sickle cell disease. We hypothesized that the growth trajectories for total GM volume, total WM volume, and regional GM volumes are altered in children with sickle cell disease compared with controls. MATERIALS AND METHODS: We analyzed T1-weighted images of the brains of 28 children with sickle cell disease (mean baseline age, 98 months; female/male ratio, 15:13) and 28 healthy age- and sex-matched controls (mean baseline age, 99 months; female/male ratio, 16:12). The total number of MR imaging examinations was 141 (2-4 for each subject with sickle cell disease, 2-3 for each control subject). Total GM volume, total WM volume, and regional GM volumes were measured by using an automated method. We used the multilevel-model-for-change approach to model growth trajectories. RESULTS: Total GM volume in subjects with sickle cell disease decreased linearly at a rate of 411 mm(3) per month. For controls, the trajectory of total GM volume was quadratic; we did not observe a significant linear decline. For subjects with sickle cell disease, we found 35 brain structures that demonstrated age-related GM volume reduction. Total WM volume in subjects with sickle cell disease increased at a rate of 452 mm(3) per month, while the trajectory of controls was quadratic. CONCLUSIONS: There was a significant age-related decrease in total GM volume in children with sickle cell disease. The GM volume reduction was spatially distributed widely across the brain, primarily in the frontal, parietal, and occipital lobes. Total WM volume in subjects with sickle cell disease increased at a lower rate than for controls.

Diffusion tensor brain MR imaging in X-linked cerebral adrenoleukodystrophy.

Brain diffusion tensor MRI of 11 boys with X-linked adrenoleukodystrophy was performed. The authors determined quantitative isotropic apparent diffusion coefficient (ADC(i)) and fractional anisotropy (FA) values in the white matter. ADC(i) and FA values in the affected white matter were significantly different from those in normal-appearing white matter. Zonal ADC(i) and FA gradations, which might originate from well-established histopathologic zonal changes, existed within affected white matter.

Diffusion tensor imaging of periventricular leukomalacia shows affected sensory cortex white matter pathways.

The authors used diffusion-tensor imaging to examine central white matter pathways in two children with spastic quadriplegic cerebral palsy. Corticospinal tracts projecting from cortex to brainstem resembled controls. In contrast, posterior regions of the corpus callosum, internal capsule, and corona radiata were markedly reduced, primarily in white matter fibers connected to sensory cortex. These findings suggest that the motor impairment in periventricular leukomalacia may, in part, reflect disruption of sensory connections outside classic pyramidal motor pathways.

Dysembryoplastic neuroepithelial tumor-like neoplasm of the septum pellucidum: a lesion often misdiagnosed as glioma: report of 10 cases.

The authors report a series of 10 low-grade neoplasms arising in the midline anteriorly in the region of the septum pellucidum with many of the histologic features of dysembryoplastic neuroepithelial tumor (DNT). The patients (five female, five male) ranged in age from 6 to 35 years (mean age, 21.5 years). The most common presenting symptoms were headache, nausea and vomiting, and visual disturbances. Radiographically, the tumors extended into the lateral ventricles from the septal region and obstructed the foramen of Monro. Varying degrees of hydrocephalus were present. The lesions were lobular, well-delineated, hypointense to brain on T1-weighted magnetic resonance imaging, and hyperintense on T2-weighted images. They were uniformly nonenhancing or showed only minimal peripheral enhancement. The tumors, in aggregate, had the histologic features of DNT. These included a mucin-rich background, oligodendrocyte-like cells, "floating neurons," and a "specific glioneuronal element." Seven patients underwent gross total resection and two underwent subtotal resection. No patients received adjuvant chemotherapy or radiotherapy. On follow-up (n = 6; median, 14 months), all tumors had either not recurred or were radiologically stable. On the basis of both neuroimaging and histopathology, DNT-like lesions should be considered in the differential diagnosis of midline intraventricular tumors in children and young adults. Distinction from more aggressive neoplasms is essential because these tumors appear to behave in a benign fashion.

SPECT imaging in cerebral vasospasm following subarachnoid hemorrhage.

UNLABELLED: Cerebral vasospasm is a frequent complication after subarachnoid hemorrhage and contributes to overall morbidity and mortality. Arteriography is the standard test for determining the presence of vasospasm. A retrospective review of 16 patients with cerebral aneurysm was undertaken to assess the sensitivity and specificity of SPECT for diagnosis of vasospasm. Fourteen patients were hospitalized after subarachnoid hemorrhage and 2 patients were hospitalized for elective aneurysmal clipping. The patients' condition on discharge was correlated to clinical and SPECT evidence of vasospasm. METHODS: Vasospasm was defined as the new onset of neurological signs and symptoms not explained by rebleed or hydrocephalus. A total of 20 SPECT studies were performed for 16 patients during their admission and 14 of 16 patients had a single angiographic study. RESULTS: Thirteen of 16 patients had 14 episodes of clinical evidence of vasospasm and 14 SPECT studies were performed in these 13 patients. The sensitivity and specificity of SPECT in this retrospective study were 89% (8/9) and 71% (5/7), respectively. Our small sample of arteriograms yielded in comparison a sensitivity of 67% (2/3) and specificity of 100% (9/9). The one false-negative SPECT study occurred in conjunction with the one false-negative arteriogram in the presence of clinical findings consistent with vasospasm. Three false-positive SPECT studies occurred in 2 patients who had perfusion abnormalities in areas of normal CT findings without clinical or arteriographic evidence of vasospasm. Five of 5 patients who died became unresponsive as a result of clinically presumed vasospasm and 4 of 5 of these patients had diffuse or hemispheric SPECT perfusion defects. Of the 11 patients who survived, none became unresponsive; 1 of 11 had positive diffuse or hemispheric perfusion defects. CONCLUSION: SPECT is a sensitive and fairly specific test for corroboration of clinical findings of vasospasm. A negative SPECT study may obviate the need for arteriography. Unresponsiveness is the best predictor of poor outcome; however, hemispheric SPECT perfusion deficits are also associated with poor outcome.

Intramedullary spinal cord tuberculoma in a patient with AIDS.

Intramedullary spinal cord tuberculoma in a young, homosexual man with AIDS was detected with the use of MR and confirmed pathologically. MR findings were similar to those seen in other intramedullary lesions, eg, astrocytoma, ependymoma, hemangioblastoma, metastasis, lymphoma, and opportunistic infections. Delineation of the lesion improved with administration of Gd-DTPA; enhancement of the lesion, however, does not always correlate with true tumor margins at pathologic examination.

A heterotopic cerebellum presenting as a suprasellar mass with associated nasopharyngeal teratoma.

We present a case of nasopharyngeal teratoma that was discovered in association with a suprasellar heterotopic cerebellum in a newborn. Well-differentiated, heterotopic, cerebellar masses have been reported in the orbits, spine, and frontal encephalocele but not, to our knowledge, in the suprasellar region. In this report, we describe the imaging findings and discuss the possible origins of the two masses discovered in this case.

Diffusion-tensor MR imaging of the human brain with gradient- and spin-echo readout: technical note.

Diffusion-tensor MR imaging of the brain is an objective method that can measure diffusion of water in tissue noninvasively. Five adult volunteers participated in this study that was performed to evaluate the potential of gradient- and spin-echo readout for diffusion-tensor imaging by comparing it with single-shot spin-echo echo-planar imaging. Gradient- and spin-echo readout provides comparable measures of water diffusion to single-shot spin-echo echo-planar readout with significantly less geometrical distortion at the expense of a longer imaging time.

Diffusion tensor MR imaging of the brain: effect of diffusion weighting on trace and anisotropy measurements.

BACKGROUND AND PURPOSE: In human brain, the relationship between MR signal and b value is complicated by cerebral perfusion, restricted diffusion, anisotropy, cellular membrane permeability, and active cellular transport of water molecules. Our purpose was to evaluate the effect of the number and strength of diffusion-sensitizing gradients on measured isotropic apparent diffusion coefficients (ADCi), fractional anisotropy (FA), and their respective SD in different anatomic locations of the brain. METHODS: Quantitative apparent diffusion coefficients and diffusion anisotropy brain maps were obtained from 10 healthy volunteers by using six different levels of diffusion weighting (b0 = 0, bl = 160, b2 = 320, b3 = 480, b4 = 640, and b5 = 800 s/mm2), applied sequentially in six different directions (Gxx, Gyy, Gzz, Gxy, Gxz, Gyz) and coupled to a single-shot spin-echo echo-planar (2,045/115 [TR/TE]) MR imaging technique. ADCi, FA, eigenvalues (lambda1, lambda2, lamdba3)1 of the principal eigenvectors, and their respective SD were measured from seven different anatomic locations in the brain. Repeated measures analysis of variance was used to evaluate for the existence of significant differences in the average and SD of the calculated ADCi and FA as a function of the number and strength of b values. When a difference existed, the Bonferroni t method was used for paired comparisons of the groups. RESULTS: The measured ADCi was affected by the number and strength of b values (P < .05). The SD of the ADCi was affected by the strength (P < .05) but not the number of b values (P > .05). The measured FA was unaffected by the number and strength of b values (P > .05). The SD was affected by the number and strength of b values (P < .05). CONCLUSION: The number and strength of b values do influence measures of diffusion and anisotropy. Attention to the choice of diffusion sensitization parameters is important in decisions regarding clinical feasibility (acquisition time) and normative measures.

GRASE (gradient- and spin-echo) MR of the brain.

PURPOSE: To assess the clinical utility of GRASE (gradient- and spin-echo) MR imaging of the brain by comparing it with the T2-weighted turbo spin-echo technique. METHODS: Fifty-three consecutive patients referred for MR imaging of the brain were studied with T2-weighted turbo spin-echo and GRASE techniques, matched for effective echo time (110 milliseconds), echo train length (eight), and spatial resolution. The examinations were evaluated independently by two neuroradiologists for lesion detection (high- and low-signal-intensity lesions) and lesion conspicuity, and for susceptibility, motion, and chemical-shift artifacts. RESULTS: The GRASE technique provided greater detection of both high- and low-signal-intensity lesions and of low-signal-intensity lesions with paramagnetic susceptibility characteristics (ie, calcium and hemorrhage). Chemical-shift artifacts in the frequency-encoding direction were more prominent with the turbo spin-echo technique, whereas chemical-shift artifacts in the phase-encoding direction were more prominent with the GRASE technique. There was no significant difference in the degree of diamagnetic susceptibility artifacts at the base of the skull, or in motion artifacts. CONCLUSION: T2-weighted GRASE is a fast imaging technique with a potential for replacing turbo spin-echo in routine MR imaging of the brain. GRASE maintains the contrast resolution of turbo spin-echo imaging and is better at depicting lesions with paramagnetic susceptibility characteristics.

Polyarteritis nodosa presenting as temporal arteritis in a 9-year-old child.

A 9-year-old Haitian girl presented initially with monocular blindness and an isolated temporal arteritis, confirmed by angiographic studies and temporal artery biopsy findings. CT and MR studies of the intracranial circulation showed only an enlarged, dense superficial temporal artery. Systemic workup revealed a mildly elevated erythrocyte sedimentation rate, mild changes in white and red blood cells, and a remote history of sensorineural hearing loss. Pathologic examination of the biopsy specimen narrowed the differential diagnosis to giant cell temporal arteritis and polyarteritis nodosa. Treatment with corticosteroids alone failed, and the child returned 1 month later with severe systemic illness and encephalopathy. MR studies showed multiple cortical and subcortical foci of increased T2 signal, and gyriform enhancement on T1-weighted images. Renal and mesenteric arteriograms showed innumerable tiny aneurysms at branch points in small and medium-sized vessels, typical of polyarteritis nodosa. We found no previous reports of this initial presentation in the pediatric population for either polyarteritis nodosa or giant cell temporal arteritis.

Spontaneous labyrinthine hemorrhage in sickle cell disease.

We report the clinical and MR imaging findings in two African-American patients with manifestations of sickle cell disease affecting the inner ear. Both suffered sudden-onset sensorineural hearing loss and vestibular symptoms, and both had high labyrinthine signal on T1-weighted MR images attributed to labyrinthine hemorrhage. Follow-up studies of the first patient revealed a decrease in abnormal vestibular signal. Careful attention to the labyrinth on T1-weighted MR images can reveal vestibulocochlear clinical findings in sickle cell patients, with important implications for management and prognosis.

Telangiectatic osteosarcoma of the skull base.

We present a patient with a distinctive lesion of the skull base, which, at imaging, showed expansile destruction of the sphenoid bone, hemorrhage with fluid-fluid levels, and contrast enhancement of a solid portion. These features ordinarily suggest either giant cell tumor or aneurysmal bone cyst; however, pathologic examination confirmed instead a rare variant of osteosarcoma of the telangiectatic type. Although imaging findings can indicate any of these possibilities, biopsy is an essential step in arriving at the diagnosis.

Multi-slice proton MR spectroscopy and diffusion-weighted imaging in methylmalonic acidemia: report of two cases and review of the literature.

SUMMARY: Methylmalonic acidemia is an inborn disorder of amino acid metabolism that commonly presents with neurologic deficits. We present the results of multi-slice proton MR spectroscopy and diffusion-weighted imaging of the brain in two patients with methylmalonic acidemia. The findings consisted of restricted diffusion and elevated lactate in the globi pallidi, compatible with acute infarction (patient 1) and elevated lactate in CSF (patient 2).