Sun Yong Kim

Optimal Diffusion-Weighted Imaging Protocol for Lesion Detection in Transient Global Amnesia

BACKGROUND AND PURPOSE: Diffusion-weighted imaging (DWI) can depict small punctate hyperintense lesions in the hippocampus in transient global amnesia (TGA). The purpose of this study was to find an optimal DWI protocol for lesion detection in TGA by investigating various imaging parameters and imaging timing after symptom onset. MATERIALS AND METHODS: Sixteen patients with TGA diagnosed during 14 months underwent DWI within 24 hours and again at follow-up 3 days after onset. Each DWI session included 4 different sequences using different b-values (seconds per square millimeter) and section thicknesses (millimeter): 1000/5, 1000/3, 2000/3, and 3000/3. The presence or absence of hyperintense lesions on the 8 DWIs was determined visually, and the number of lesions detected was compared. RESULTS: Thirteen of the 16 patients (81%) had either single or multiple punctate hyperintense lesions, totaling 24 lesions, and the remaining 3 patients had no lesions. All lesions detected were in the hippocampus except 1. The number of lesions detected on initial DWIs at a b-value/section thickness of 1000/5, 1000/3, 2000/3, and 3000/3 was 3, 9, 13, and 13, respectively, whereas that of follow-up DWIs was 17, 22, 24, and 24, respectively. CONCLUSION: On the basis of these preliminary results, the highest lesion detection was achieved for DWI with b = 2000/3 mm or b = 3000/3 mm at 3 days postonset. When no lesion is detected by DWI within 24 hours after onset, follow-up DWI is recommended several days later.

Posttreatment High-Grade Glioma: Usefulness of Peak Height Position with Semiquantitative MR Perfusion Histogram Analysis in an Entire Contrast-enhanced Lesion for Predicting Volume Fraction of Recurrence

PURPOSE To determine whether semiquantitative histogram analysis of the normalized cerebral blood volume (CBV) for an entire contrast material-enhanced lesion could be used to predict the volume fraction of posttreatment high-grade glioma recurrence compared with posttreatment change. MATERIALS AND METHODS The institutional review board approved this retrospective study. Informed consent was obtained. Thirty-nine patients with pathologically proved predominant tumor recurrence (tumor recurrence group, tumor fraction > or =50% [n = 14]), mixed tumor and posttreatment change (mixed group, tumor fraction > or =20% and <50% [n = 10]), and predominant posttreatment change (treatment change group, tumor fraction <20% [n = 15]) were evaluated. Histogram parameters of normalized CBV-histogram width, peak height position (PHP), and maximum value (MV)-were measured in entire contrast-enhanced lesions and used as discriminative indexes. Ordered logistic regression was used to determine independent factors for predicting the diseases of posttreatment contrast-enhanced lesions. Leave-one-out cross-validation was used to determine diagnostic accuracy. RESULTS PHP was an independent predictive factor (P = .003) for differentiating contrast-enhanced lesions in patients with posttreatment gliomas. According to receiver operating characteristic curve analyses, PHP provided sensitivity of 90.2% and specificity of 91.1% for differentiating tumor recurrence from mixed and treatment change groups at an optimum threshold of 1.7 by using leave-one-out cross-validation. MV helped distinguish treatment change group from tumor recurrence and mixed groups at an optimum threshold of 2.6 (sensitivity, 96.5%; specificity, 93.1%). CONCLUSION PHP can be used to predict the volume fraction of posttreatment high-grade glioma recurrence.

Which CT perfusion parameter best reflects cerebrovascular reserve?: correlation of acetazolamide-challenged CT perfusion with single-photon emission CT in Moyamoya patients.

BACKGROUND AND PURPOSE: CT perfusion (CTP) is a more readily accessible method for evaluation of cerebral perfusion than single-photon emission CT (SPECT). We assessed whether there is any resting or drug-challenged CTP parameter correlating with cerebrovascular reserve (CVR) obtained by SPECT in Moyamoya patients. MATERIALS AND METHODS: Normalized baseline CTP parameters and their percentage changes were calculated in 152 regions of interest (ROIs). On qualitative SPECT analysis, each ROI was classified in either the “impaired CVR” or “normal CVR” group. Quantitative CVR was calculated by using normalized SPECT values before and after acetazolamide administration. Baseline CTP parameters and their percentage changes were compared with qualitative and quantitative CVRs. Receiver operating characteristic (ROC) curve analysis defined the threshold values of CTP parameters that best predict impaired qualitative CVR. RESULTS: The mean values of CTP parameters were significantly different between normal and impaired CVR groups. The percentage change of cerebral blood flow (pcCBF) was correlated most significantly with quantitative CVR (r = 0.89; P < .05). The correlation coefficients between the baseline CTP parameters and quantitative CVR were poor or not significant. The ROC-derived threshold values of pcCBF and mean transit time determined impaired CVR with a sensitivity of 94.4 and 85.2; specificity of 93.2 and 65.9; positive predictive value of 97.1 and 86.0; and negative predictive value of 87.2 and 64.4, respectively. CONCLUSION: Baseline CTP parameters are not reliable for predicting impaired CVR. However, pcCBF correlated strongly with quantitative CVR; therefore, CTP evaluation for CVR in Moyamoya patients requires normalization and acetazolamide challenge.

The optical and structural properties of AlN thin films characterized by spectroscopic ellipsometry

Spectroscopic ellipsometry (SE) was used to characterize AlN thin films deposited on SiO2/Si substrates by r.f. magnetron sputtering. Refractive index and thickness of each layer were extracted from the SE data analysis employing a multi-layer model and effective medium approximation. Non-destructive characterization of multi-layer films, with total thickness up to 2.5 mm, was successfully carried out, despite of the strong correlation between the film parameters such as thickness and surface roughness. The refractive indices of the AlN films were in the range of 1.98‐2.15, which are typical values for polycrystalline AlN. The good agreement between the results of SE and those from X-ray diffraction (XRD), atomic force microscopy (AFM) and scanning electron microscopy (SEM), regarding crystallinity, rms roughness, and thickness of the films, confirms that spectroscopic ellipsometry is a useful tool to extract the information on the film quality and uniformity. q 2000 Elsevier Science S.A. All rights reserved.

Diagnostic accuracy and interobserver variability of pulsed arterial spin labeling for glioma grading

Background: Although pulsed arterial spin labeling (PASL) enables the reliable qualitative grading of brain tumors, its use in quantification for glioma grading may be hampered by the limited interobserver variability associated with low spatial resolution. Purpose: To assess the interobserver variability and diagnostic accuracy of the relative tumor perfusion signal intensity (rTPS) calculated using PASL in glioma grading. Material and Methods: Fifty-eight patients with 61 cerebral astrocytomas underwent conventional MR imaging and PASL. Receiver operating characteristic analyses were used to determine the optimum thresholds for tumor grading. The sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV) for identifying high-grade gliomas were also calculated. Cohens κ statistic was used to determine the levels of interobserver variability in the quantitative analysis of PASL. Results: The sensitivity, specificity, PPV, and NPV for determining a high-grade glioma with conventional MR imaging were 77.1, 73.1, 79.4, and 70.4%, respectively. A threshold value of 1.28 for rTPS provided a sensitivity, specificity, PPV, and NPV of 82.9, 96.2, 96.7, and 80.6%, respectively. There was a statistically significant difference in the rTPS between low- and high-grade astrocytomas (1.14 vs. 1.47, P<0.05). In the interobserver variability analysis, substantial agreement was obtained for the quantitative rTPS measurement from PASL (κ =0.72). Conclusion: Quantitative perfusion measurement with PASL can improve the diagnostic accuracy of preoperative glioma grading, as compared to the application of conventional imaging alone. However, the interobserver variability for quantification is substantial.

Early experiences of elective stenting for symptomatic stenosis of the M1 segment of the middle cerebral artery: reports of three cases and review of the literature

The role of stenting in the treatment of patients with middle cerebral artery stenosis is not defined because of the high risk and difficulty in tracking. However, recent improvements in the technology, in particular of small, flexible stents and of small, flexible stents with accumulative stenting experience in occlusive intracranial disease endovascular treatment of this disease is now possible. We treated three patients with a symptomatic stenosis of the M1 segment of the middle cerebral artery despite combination anticoagulation therapy. All patients were successfully treated with a balloon-expandable S660 coronary stent. No procedure-related complications occurred and all patients were discharged and remained neurologically stable during the follow-up period (2-12 months). We propose stenting as one of the treatment modalities in patients with symptomatic stenosis of the M1 segment of the middle cerebral artery in selected cases. However, further studies on this new procedure should be done to determine its effect on long-term stroke prevention and to compare its safety with other treatment options.

Forced Arterial Suction Thrombectomy with the Penumbra Reperfusion Catheter in Acute Basilar Artery Occlusion: A Retrospective Comparison Study in 2 Korean University Hospitals

BACKGROUND AND PURPOSE: A performance of forced arterial suction thrombectomy was not reported for the treatment of acute basilar artery occlusion. This study compared revascularization performance between intra-arterial fibrinolytic treatment and forced arterial suction thrombectomy with a Penumbra reperfusion catheter in patients with acute basilar artery occlusion. MATERIALS AND METHODS: Fifty-seven patients with acute basilar artery occlusion were treated with intra-arterial fibrinolysis (n = 25) or forced arterial suction thrombectomy (n = 32). Baseline characteristics, successful revascularization rate, and clinical outcomes were compared between the groups. RESULTS: Baseline characteristics, the frequency of patients receiving intravenous recombinant tissue plasminogen activator, and mean time interval between symptom onset and femoral puncture did not differ between groups. The forced arterial suction thrombectomy group had a shorter procedure duration (75.5 minutes versus 113.3 minutes, P = .016) and higher successful revascularization rate (88% versus 60%, P = .017) than the fibrinolysis group. Fair outcome, indicated by a modified Rankin Scale 0–3, at 3 months was achieved in 34% of patients undergoing forced arterial suction thrombectomy and 8% of patients undergoing fibrinolysis (P = .019), and the mortality rate was significantly higher in the fibrinolysis group (25% versus 68%, P = .001). Multiple logistic regression analysis identified the forced arterial suction thrombectomy method as an independent predictor of fair outcome with adjustment for age, sex, initial NIHSS score, and the use of intravenous recombinant tissue plasminogen activator (odds ratio, 7.768; 95% CI, 1.246–48.416; P = .028). CONCLUSIONS: In acute basilar artery occlusion, forced arterial suction thrombectomy demonstrated a higher revascularization rate and improved clinical outcome compared with traditional intra-arterial fibrinolysis. Further clinical trials with the newer Penumbra catheter are warranted.

Growth mechanisms and structural properties of microcrystalline silicon films deposited by catalytic CVD

Abstract Silicon–hydrogen bonding configurations, during or after microcrystalline silicon (μc-Si:H) film deposition by catalytic CVD, have been investigated for the first time by real-time in-situ Fourier transform phase modulated infrared ellipsometry (FTPME). FTPME measurements have been performed during and after μc-Si:H film depositions using high, low or variable dilutions of silane in hydrogen. The silicon–hydrogen bonding configurations of μc-Si:H films have been correlated with their corresponding structural properties as deduced from UV-visible ellipsometry analyses. A 4.6% efficiency has been obtained for μc-Si:H n-i-p solar cells, with the i-layer deposited by catalytic CVD at 200°C on a glass substrate using a variable hydrogen dilution process. Further optimization should improve the performance of catalytic CVD μc-Si:H solar cells.

Underestimation of Cerebral Perfusion on Flow-Sensitive Alternating Inversion Recovery Image: Semiquantitative Evaluation with Time-to-Peak Values

BACKGROUND AND PURPOSE: We assessed the underestimation of cerebral perfusion measured by the flow-sensitive alternating inversion recovery (FAIR) technique in patients with carotid stenosis and compared the technique with dynamic susceptibility contrast (DSC) MR images. MATERIALS AND METHODS: We studied 42 areas of decreased cerebral blood flow (CBF) using 3 FAIR images with different inversion times (TIs) in 42 consecutive patients with unilateral carotid stenosis of more than 50%. The width of decreased CBF area (wCBF) was qualitatively assessed. We analyzed the ratio of CBF (rCBF) and the time-to-peak (TTP) difference (dTTP) between the ipsilateral hemisphere to carotid stenosis and contralateral normal area using regions of interest (ROIs) at the same location. RESULTS: In the areas with more prolonged TTP (dTTP ≥3.2 s), the wCBF obtained from the FAIR images with TI of 1600 ms was smaller than those from the FAIR images with a TI of 800 ms and 1200 ms in all cases. The mean rCBF obtained from the FAIR images with a TI of 1200 ms was significantly lower than that obtained from the FAIR images with a TI of 1600 ms (P < .01) in the areas with more prolonged TTP. In the areas with less prolonged TTP (dTTP <3.2 s), the wCBF and mean rCBF were not significantly different between the 2 FAIR images (TI, 1200 and 1600 ms). CONCLUSION: If TTP is delayed significantly (dTTP ≥3.2 s), the FAIR with intermediate or short TI showed underestimation of perfusion in the same area with delay in TTP.

Quantitative Analysis of Developmental Process of Cranial Suture in Korean Infants

Objective The purpose of this study was to elucidate the anatomical development of physiologic suture closure processes in infants using three dimensional reconstructed computed tomography (CT). Methods A consecutive series of 243 infants under 12 months of age who underwent three dimensional CT were included in this study. Four major cranial sutures (sagittal, coronal, lambdoidal and metopic suture) were classified into four suture closure grades (grade 0=no closure along the whole length, grade 1=partial or intermittent closure, grade 2=complete closure with visible suture line, grade 3=complete fusion (ossification) without visible suture line), and measured for its closure degree (suture closure rates; defined as percentage of the length of closed suture line divided by the total length of suture line). Results Suture closure grade under 12 months of age comprised of grade 0 (n=195, 80.2%), grade 1 (n=24, 9.9%) and grade 2 (n=24, 9.9%) in sagittal sutures, whereas in metopic sutures they were grade 0 (n=61, 25.1%), grade 1 (n=167, 68.7%), grade 2 (n=6, 24%) and grade 3 (n=9, 3.7%). Mean suture closure rates under 12 months of age was 58.8% in metopic sutures, followed by coronal (right : 43.8%, left : 41.1%), lambdoidal (right : 27.2%, left : 25.6%) and sagittal sutures (15.6%), respectively. Conclusion These quantitative descriptions of cranial suture closure may help understand the process involved in the cranial development of Korean infants.