Shuichi Higano

Evaluation of regional differences of tracer appearance time in cerebral tissues using [15O] water and dynamic positron emission tomography.

The tracer appearance time relative to the radial artery–sampling site has been evaluated in six brain locations in five human subjects using dynamic positron emission tomography (PET) following the bolus injection of H215O. There was a maximum difference of ± 2 s from the average in each location. T o globally adjust the timing difference between the measured arterial curve and the PET scan, a correction method was developed based on a nonlinear least-squares fitting procedure. This new technique determined the global time delay with an accuracy of ± 0.5 s. On the other hand, the linear backward extrapolation method resulted in a systematic error of 4 s.

A method to quantitate cerebral blood flow using a rotating gamma camera and iodine-123 iodoamphetamine with one blood sampling

A method has been developed to quantitate regional cerebral blood blow (rCBF) using iodine-123-labelled N-isopropyl-p-iodoamphetamine (IMP). This technique requires only two single-photon emission tomography (SPET) scans and one blood sample. Based on a two-compartment model, radioactivity concentrations in the brain for each scan time (early: te; delayed: td) aredescribed as: % MathType!MTEF!2!1!+-% feaafiart1ev1aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn% hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr% 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9% vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x% fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGaam4qamaaBa% aaleaacaWG0baabeaakmaabmaabaGaamiDamaaBaaaleaacaWGLbaa% beaaaOGaayjkaiaawMcaaiabg2da9iaadAgacqWIpM+zcaWGdbWaaS% baaSqaaiaadggaaeqaaOWaaeWaaeaacaWG0bWaaSbaaSqaaiaadwga% aeqaaaGccaGLOaGaayzkaaGaey4LIqSaamyzamaalaaabaGaamOzaa% qaaiaadAfadaWgaaWcbaGaamizaaqabaaaaOGaamiDamaaBaaaleaa% caWGLbaabeaaaaa!4D64!\[C_t \left( {t_e } \right) = fC_a \left( {t_e } \right) \otimes e\frac{f}{{V_d }}t_e \] and % MathType!MTEF!2!1!+-% feaafiart1ev1aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn% hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr% 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9% vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x% fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGaam4qamaaBa% aaleaacaWG0baabeaakmaabmaabaGaamiDamaaBaaaleaacaWGKbaa% beaaaOGaayjkaiaawMcaaiabg2da9iaadAgacqWIpM+zcaWGdbWaaS% baaSqaaiaadggaaeqaaOWaaeWaaeaacaWG0bWaaSbaaSqaaiaadsga% aeqaaaGccaGLOaGaayzkaaGaey4LIqSaamyzamaalaaabaGaamOzaa% qaaiaadAfadaWgaaWcbaGaamizaaqabaaaaOGaamiDamaaBaaaleaa% caWGKbaabeaaaaa!4D61!\[C_t \left( {t_d } \right) = fC_a \left( {t_d } \right) \otimes e\frac{f}{{V_d }}t_d \] respectively, where ⊗ denotes the convolution integral; Ca(t), the arterial input function; f rCBF; and Vd, the regional distribution volume of IMP. Calculation of the ratio of the above two equations and a “table look-up” procedure yield a unique pair of rCBF and Vd for each region of interest (ROI). A standard input function has been generated by combining the input functions from 12 independent studies prior to this work to avoid frequent arterial blood sampling, and one blood sample is taken at 10 min following IMP administration for calibration of the standard arterial input function. This calibration time was determined such that the integration of the first 40 min of the calibrated, combined input function agreed best with those from 12 individual input functions (the difference was 5.3% on average). This method was applied to eight subjects (two normals and six patients with cerebral infarction), and yielded rCBF values which agreed well with those obtained by a positron emission tomography H215O autoradiography method. This method was also found to provide rCBF values that were consistent with those obtained by the non-linear least squares fitting technique and those obtained by conventional microsphere model analysis. The optimum SPET scan times were found to be 40 and 180 min for the early and delayed scans, respectively. These scan times allow the use of a conventional rotating gamma camera for clinical purposes. Vd values ranged between 10 and 40 ml/g depending on the pathological condition, thereby suggesting the importance of measuring Vd for each ROI. In conclusion, optimization of the blood sampling time and the scanning time enabled quantitative measurement of rCBF with two SPET scans and one blood sample.

Comparison of ipsilateral activation between right and left handers: a functional MR imaging study.

WE used fMRI to compare the ipsilateral activation in the sensorimotor region (SMR) during dominant and non-dominant hand motor tasks between right and left handers. In right handers, the ipsilateral activation was significantly greater during non-dominant (left) hand task than dominant (right) hand task, while in left handers, it showed no significant difference. The ipsilateral activation was most pronounced in the precentral subregion (presumably corresponding to the premotor area) during either hand task in both groups. We conclude that the different patterns of ipsilateral activation might be mainly explained by the hemispheric dominance. The skill of the hand and complexity of tasks may be related to the predominant activation of the premotor area.

Usefulness of contrast-enhanced T1-weighted sampling perfection with application-optimized contrasts by using different flip angle evolutions in detection of small brain metastasis at 3T MR imaging: comparison with magnetization-prepared rapid acquisition of gradient echo imaging.

BACKGROUND AND PURPOSE: Early accurate diagnosis of brain metastases is crucial for a patients prognosis. This study aimed to compare the conspicuity and detectability of small brain metastases between contrast-enhanced 3D fast spin-echo (sampling perfection with application-optimized contrasts by using different flip angle evolutions [SPACE]) and 3D gradient-echo (GE) T1-weighted (magnetization-prepared rapid acquisition of GE [MPRAGE]) images at 3T. MATERIALS AND METHODS: Sixty-nine consecutive patients with suspected brain metastases were evaluated prospectively by using SPACE and MPRAGE on a 3T MR imaging system. After careful evaluation by 2 experienced neuroradiologists, 92 lesions from 16 patients were selected as brain metastases. We compared the shorter diameter, contrast rate (CR), and contrast-to-noise ratio (CNR) of each lesion. Diagnostic ability was compared by using receiver operating characteristic (ROC) analysis. Ten radiologists (5 neuroradiologists and 5 residents) participated in the reading. RESULTS: The mean diameter was significantly larger by using SPACE than MPRAGE (mean, 4.5 ± 3.7 versus 4.3 ± 3.7 mm, P = .0014). The CR and CNR of SPACE (mean, 57.3 ± 47.4%, 3.0 ± 1.9, respectively) were significantly higher than those of MPRAGE (mean, 37.9 ± 41.2%, 2.6 ± 2.2; P < .0001, P = .04). The mean area under the ROC curve was significantly larger with SPACE than with MPRAGE (neuroradiologists, 0.99 versus 0.88, P = .013; residents, 0.99 versus 0.78, P = .0001). CONCLUSIONS: Lesion detectability was significantly higher on SPACE than on MPRAGE, irrespective of the experience of the reader in neuroradiology. SPACE should be a promising diagnostic technique for assessing brain metastases.

Linearization Correction of 99mTc-Labeled Hexamethyl-Propylene Amine Oxime (HM-PAO) Image in Terms of Regional CBF Distribution: Comparison to C15O2 Inhalation Steady-State Method Measured by Positron Emission Tomography:

The radioisotope distribution following intravenous injection of 99mTc-labeled hexamethylpropyleneamine oxime (HM-PAO) in the brain was measured by single photon emission computed tomography (SPECT) and corrected for the nonlinearity caused by differences in net extraction. The “linearization” correction was based on a three compartment model, and it required a region of reference to normalize the SPECT image in terms of regional cerebral blood flow distribution. Two different regions of reference, the cerebellum and the whole brain, were tested. The uncorrected and corrected HM-PAO images were compared with cerebral blood flow (CBF) image measured by the C15O2 inhalation steady state method and positron emission tomography (PET). The relationship between uncorrected HM-PAO and PET–CBF showed a correlation coefficient of 0.85 but tended to saturate at high CBF values, whereas it was improved to 0.93 after the “linearization” correction. The whole-brain normalization worked just as well as normalization using the cerebellum. This study constitutes a validation of the “linearization” correction and it suggests that after linearization the HM-PAO image may be scaled to absolute CBF by employing a global hemispheric CBF value as measured by the nontomographic 133Xe clearance method.

Predominant Involvement of Ipsilateral Anterior and Posterior Circulations in Moyamoya Disease

Background and Purpose— We encountered several patients with childhood onset of moyamoya disease in whom the ipsilateral anterior and posterior circulations were predominantly involved. This study investigated whether this is an angiographic characteristic of this disease. Methods— We evaluated steno-occlusive lesions on angiograms of 85 patients with pediatric onset of moyamoya disease, using two 4-stage angiographic classification scales for the internal carotid artery and posterior cerebral artery systems (ICA and PCA staging, respectively) and determined whether lesions with more advanced ICA and PCA stages were on ipsilateral sides. Results— When positive laterality was defined as the presence of a difference by ≥1 stage between the stages on both sides, lateralities in the ICA stages and in the PCA stages were present in 40 (47%) and 27 patients (32%), respectively. Lesions with more advanced ICA and PCA stages were on the same side, with significant probability (P =0.024, Fisher’s exact test). Lateralities in both ICA and PCA lesions were found in 17 patients. In 14 (82%) of the 17 patients, the more advanced side of ICA lesions was the same as that of PCA lesions, while it was contralateral in 3 patients (18%). Conclusions— In pediatric-onset moyamoya disease, asymmetrical involvement of bilateral ICAs and PCAs was common, and the ipsilateral ICA and PCA tended to be predominantly involved.

Quantitative Assessment of the Pharyngeal Airway by Dynamic Magnetic Resonance Imaging in Obstructive Sleep Apnea Syndrome

Dynamic changes in the pharyngea airway of patients with obstructive sleep apnea syndrome (OSAS) were evaluated by quantitating the findings of real-time imaging performed during wakefulness and spontaneous sleep by means of dynamic magnetic resonance imaging (MRI). Six patients with OSAS and 3 non-OSAS subjects, selected prospectively and randomly, underwent polysomnography and dynamic MRI. The cross-sectional areas of the soft palate and oropharynx and the anterior-posterior airway dimensions seen during wakefulness and spontaneous sleep were calculated by US National Institutes of Health imaging software. On the basis of a case control study, comparisons were made with age-matched and body mass index—matched obese non-OSAS snorers. Spontaneous sleep caused significant obstruction and narrowing of various sites of the pharyngeal airway in the OSAS patients, but not in the non-OSAS subjects. During wakefulness, the non-OSAS subjects showed no marked narrowing of the pharyngeal airways, whereas a transient but significant narrowing was observed in the OSAS patients. The mean values of both the cross-sectional area and the anterior-posterior diameter at the soft palate were significantly reduced by spontaneous sleep in the OSAS patients. Dynamic MRI in awake OSAS patients shows promise as a routine diagnostic tool for localizing the upper airway collapse for appropriate selection of surgical therapy.

The Leptomeningeal "Ivy Sign" on Fluid-Attenuated Inversion Recovery MR Imaging in Moyamoya Disease: A Sign of Decreased Cerebral Vascular Reserve?

BACKGROUND AND PURPOSE: Moyamoya disease is an idiopathic occlusive cerebrovascular disorder with abnormal microvascular proliferation. We investigated the clinical utility of leptomeningeal high signal intensity (ivy sign) sometimes seen on fluid-attenuated inversion recovery images in Moyamoya disease. MATERIALS AND METHODS: We examined the relationship between the degree of the ivy sign and the severity of the ischemic symptoms in 96 hemispheres of 48 patients with Moyamoya disease. We classified each cerebral hemisphere into 4 regions from anterior to posterior. In 192 regions of 24 patients, we examined the relationship between the degree of the ivy sign and findings of single-photon emission CT, including the resting cerebral blood flow (CBF) and cerebral vascular reserve (CVR). RESULTS: The degree of the ivy sign showed a significant positive relationship with the severity of the ischemic symptoms (P < .001). Of the 4 regions, the ivy sign was most frequently and prominently seen in the anterior part of the middle cerebral artery region. The degree of the ivy sign showed a negative relationship with the resting CBF (P < .0034) and a more prominent negative relationship with the CVR (P < .001). CONCLUSIONS: The leptomeningeal ivy sign indicates decreased CVR in Moyamoya disease.

Diffusion tensor imaging fiber tractography for evaluating diffuse axonal injury.

Patients with Diffuse axonal injury (DAI) frequently exhibit cognitive disorders chronically. Radiologic recognition of DAI can help understand the clinical syndrome and to make treatment decisions. However, CT and conventional MRI are often normal or demonstrate lesions that are poorly related to the cognitive disorders. Recently, diffusion tensor imaging (DTI) fiber tractography has been shown to be useful in detecting various types of white matter damage. The aim of this study was to evaluate the feasibility of using DTI fiber tractography to detect lesions in DAI patients, and to correlate the DAI lesions with the cognitive disorders. We investigated two patients with chronic DAI. Both had impaired intelligence, as well as attention and memory disorders that restricted their activities of daily living. In both patients, DTI fiber tractography revealed interruption of the white matter fibers in the corpus collosum and the fornix, while no lesions were found on conventional MRI. The interruption of the fornix which involves the circuit of Papez potentially correlates with the memory disorder. Therefore, DTI fiber tractography may be a useful technique for the evaluation of DAI patients with cognitive disorders.

Minimum apparent diffusion coefficient is significantly correlated with cellularity in medulloblastomas

Abstract Objective: On diffusion-weighted magnetic resonance (MR) images, posterior fossa tumors may exhibit the various signal intensity and apparent diffusion coefficient (ADC) reflecting their histology and cellularity. The purpose of this study was to evaluate the relationship between ADC and tumor cellularity in medulloblastoma and other posterior fossa tumors. Methods: Pre-operative diffusion-weighted MR images were retrospectively reviewed in 26 patients with posterior fossa neoplasms: 11 medulloblastomas, one atypical teratoid/rhabdoid tumor (AT/RT), four glioblastomas, four ependymomas, three pilocytic astrocytomas and three hemangioblastomas. The minimum ADC (minADC) value of each tumor was determined on ADC maps derived from isotropic diffusion-weighted MR images. The minADC values were compared by a two-tailed t-test. Tumor cellularity measured in surgical specimens was compared with the minADC value by simple linear regression analysis. Results: The mean minADC value of the medulloblastoma was significantly lower than those of ependymoma, pilocytic astrocytoma and hemangioblastoma without overlap in the range of minADC values. Therefore, medulloblastomas could be clearly differentiated by absolute minADC values. AT/RT and glioblastoma had similar minADC values to medulloblastoma. Tumor cellularity was negatively correlated with the minADC value in medulloblastomas and other posterior fossa tumors. Discussion: The low minADC value of medulloblastomas reflects the high tumor cellularity. Analysis of ADC values has high predictive value for the differentiation of medulloblastoma from other posterior fossa tumors.