g-Yu Chen

Principles and Limitations of Computational Algorithms in Clinical Diffusion Tensor MR Tractography

SUMMARY: There have been numerous reports documenting the graphic reconstruction of 3D white matter architecture in the human brain by means of diffusion tensor MR tractography. Different from other reviews addressing the physics and clinical applications of DTI, this article reviews the computational principles of tractography algorithms appearing in the literature. The simplest voxel-based method and 2 widely used subvoxel approaches are illustrated first, together with brief notes on parameter selection and the restrictions arising from the distinct attributes of tract estimations. Subsequently, some advanced techniques attempting to offer improvement in various aspects are briefly introduced, including the increasingly popular research tracking tool using HARDI. The article explains the inherent technical limitations in most of the algorithms reported to date and concludes by providing a reference guideline for formulating routine applications of this important tool to clinical neuroradiology in an objective and reproducible manner.

PROPELLER-EPI with parallel imaging using a circularly symmetric phased-array RF coil at 3.0 T : Application to high-resolution diffusion tensor imaging

A technique integrating multishot periodically rotated overlapping parallel lines with enhanced reconstruction (PROPELLER) and parallel imaging is presented for diffusion echo‐planar imaging (EPI) at high spatial resolution. The method combines the advantages of parallel imaging to achieve accelerated sampling along the phase‐encoding direction, and PROPELLER acquisition to further decrease the echo train length (ETL) in EPI. With an eight‐element circularly symmetric RF coil, a parallel acceleration factor of 4 was applied such that, when combined with PROPELLER acquisition, a reduction of geometric distortions by a factor substantially greater than 4 was achieved. The resulting phantom and human brain images acquired with a 256 × 256 matrix and an ETL of only 16 were visually identical in shape to those acquired using the fast spin‐echo (FSE) technique, even without field‐map corrections. It is concluded that parallel PROPELLER‐EPI is an effective technique that can substantially reduce susceptibility‐induced geometric distortions at high field strength. Magn Reson Med, 2006.

Diffusion-tensor MR imaging for evaluation of the efficacy of hyperbaric oxygen therapy in patients with delayed neuropsychiatric syndrome caused by carbon monoxide inhalation

The purpose of this study is to assess the efficacy of hyperbaric oxygen therapy (HBOT) in patients with delayed neuropsychiatric syndrome (DNS) caused by carbon monoxide (CO) inhalation using diffusion tensor magnetic resonance (MR) imaging and neuropsychological test. Conventional and diffusion tensor brain MR imaging exams were performed in six patients with DNS immediately before and 3 months after the HBOT to obtain fractional anisotropy (FA) values. Six age‐ and sex‐matched normal control subjects also received MR exams for comparison. Mini‐Mental State Examination (MMSE) was also performed in patients immediately before and 3 months after the HBOT. A significantly higher mean FA value was found in control subjects as compared with the patients both before and 3 months after the HBOT (P < 0.001). The mean FA value 3 months after the HBOT was also significantly higher than that before the HBOT in the patient group (P < 0.001). All of the patients regained full scores in the MMSE 3 months after the HBOT. Diffusion tensor MR imaging can be a quantitative method for the assessment of the white matter change and monitor the treatment response in patients of CO‐induced DNS with a good clinical correlation. HBO may be an effective therapy for DNS.

Giant arachnoid granulation mimicking dural sinus thrombosis in a boy with headache: MRI

Abstract We report MRI and angiographic findings of an unusual giant arachnoid granulation in the left sigmoid sinus in a boy with headache. Its signal intensity was lower than that of cerebral cortex on T1-weighted images and higher on T2 weighting, mimicking dural sinus thrombosis.

Are the Local Blood Oxygen Level–Dependent (BOLD) Signals Caused by Neural Stimulation Response Dependent on Global BOLD Signals Induced by Hypercapnia in the Functional MR Imaging Experiment? Experiments of Long-Duration Hypercapnia and Multilevel Carbon Dioxide Concentration

BACKGROUND AND PURPOSE: The relationship between the local blood oxygen level–dependent (BOLD) signals caused by neural stimulation (fBOLD) and the global BOLD signals induced by hypercapnia (hBOLD) has not been fully investigated. In this study, we examine whether fBOLD is modulated by hBOLD signals, by means of experiments using a relatively wide range of inhaled carbon dioxide (CO2) for a long duration of 5 minutes. MATERIALS AND METHODS: Ten healthy volunteers were recruited, each undergoing 6 separate experiments by inhaling gas mixtures with different fractions of CO2 (room air, 3%–7%). Each experiment contained 3 phases, prehypercapnic, hypercapnic, and posthypercapnic, during which boxcar visual stimulus was given. The local fBOLD signals were measured from areas showing activation patterns highly correlated with the visual stimulus paradigm, whereas the global hBOLD signals were measured from areas showing no visual activations. Percentage changes in fBOLD during transient-state hypercapnia and steady-state hypercapnia were both investigated in response to varying degrees of hypercapnic perturbations. RESULTS: The hBOLD signals increased with increase of inhaled CO2 fractions. The duration for the hBOLD signals to reach steady state prolonged with increase of inhaled CO2 fractions. Normalized fBOLD ratio was inversely related to the inhaled CO2 during steady-state hypercapnia but showed positive association with hBOLD during transient-state hypercapnia. CONCLUSION: Our study concludes that the steady-state fBOLD signal intensity is dependent on and inversely related to the hBOLD signals. Previous reports documenting independent and additive relationships between hBOLD and fBOLD may likely be due to transient-state observations.

Congenital Brain Anomalies

Congenital brain malformations are abnormal developments of the brain that occur during intrauterine life. These anomalies of the central nervous system cause approximately 25% of perinatal deaths1 and account for one third of all major anomalies diagnosed at or after birth.2 The causes of congenital brain anomalies are poorly understood, although some clinical and experimental evidence indicates that a variety of factors, including genetic (chromosome abnormality), environmental (ionizing radiation, toxic agents), infection (rubella and cytomegalovirus), and nutrition (hypervitaminosis A) might play roles.3–5 Generally, developmental malformations are either a morphological abnormality (organogenesis) or an abnormal cellular differentiation (histogenesis).

Extratesticular epidermoid cyst mimicking enlarged testis

Epidermoid cysts are benign simple epithelial tumors usually appearing as hypoechoic lesions with scattered echogenic reflectors on sonography. Herein, we present a 53-year-old man with an extratesticular epidermoid cyst in the right scrotum which shows confusing sonographic findings, normal-appearing echogenicity of the lesion and atrophied testis, which lead to a diagnostic dilemma. With a variety of sonographic presentations in extratesticular epidermoid cysts, magnetic resonance (MR) imaging could play a complementary role in difficult cases.

Physiological noise suppression for functional magnetic resonance imaging by normalized least mean square adaptive filtering

F”“ctl”nal magnetx res”nance imaging (tMR1) has been widely employed as a noninvasive, radiation-free and high spatial-temporal resolution neuroimaging tool. However. loterference could mask “ot the presence of functional actlwties “wing to inherently low sensitivity of the funcuonal signal. Examples include physiological noise due to cardiac or respiratory pulsation, which has been shown to cause signal fluctuauons in certain brain areas. In thn study, we propose the application of a normalized lea\! meal square adaptive filter (NLMSADF) (3) for a suppression of the physiological noise usmg its leaning nature. M&orh and Materials NLMSADF (Fig. 1) has been widely used for its computational simpliaty. By minimizing the mean square error, the filter coefficient adaptation is given by:

Middle Cerebral Artery Calcification: Association With Ischemic Stroke

AbstractCalcification of the middle cerebral artery (MCA) is uncommon in the healthy elderly. Whether calcification of the MCA is associated with cerebral ischemic stroke remains undetermined. We intended to investigate the association using Agatston calcium scoring of the MCA. This study retrospectively included 354 subjects with ischemic stroke in the MCA territory and 1518 control subjects who underwent computed tomography (CT) of the brain. We recorded major known risk factors for ischemic stroke, including age, gender, hypertension, diabetes mellitus, smoking, hyperlipidemia, and obesity, along with the MCA calcium burden, measured with the Agatston calcium scoring method. Univariate and modified logistic regression analyses were performed to examine the association between the MCA calcification and ischemic stroke.The univariate analyses showed significant associations of ischemic stroke with age, hypertension, diabetes mellitus, smoking, total MCA Agatston score, and the presence of calcification on both or either side of the MCA. Subjects with the presence of MCA calcification on both or either side of the MCA were 8.46 times (95% confidence interval, 4.93–14.53; P < 0.001) more likely to have a cerebral infarct than subjects without MCA calcification after adjustment for the major known risk factors, including age, hypertension, diabetes mellitus, and smoking. However, a higher degree of MCA calcification reflected by the Agatston score was not associated with higher risk of MCA ischemic stroke after adjustment for the confounding factors and presence of MCA calcification. These results suggest that MCA calcification is associated with ischemic stroke in the MCA territory. Further prospective studies are required to verify the clinical implications of the MCA calcification.

337 Cerebrospinal Fluid Flow Quantification of the Cerebral Aqueduct in Children and Adults with Two-Dimentional Cine Phase-Contrast Cine MR Imaging

Background and Aims Cerebrospinal fluid (CSF) is known mainly involved in the intracranial homeostatic balance. Disruption of CSF flow may cause distinctive diseases. Therefore, the characterization of normal CSF flow dynamics in children and adults can provide pathophysiological information on diseases affecting CSF circulation. However, available measurements of CSF dynamics are too invasive and the data of children are limited. To quantify differences of CSF dynamics between children and adults, a non-invasive and powerful technique, cine phase-contrast MRI with high temporal and spatial resolution, is used for the quantification of the CSF flow. Methods Aqueductal area was selected for the quantification of CSF flow using cine-phase contrast MRI. CSF flow parameters, including peak velocity and net stroke volume, were analyzed between child-age group and adult-age group. Results 20 children (16 male, 4 female; 7 months to 6 years) with initially under clinical suspicion of atypical febrile seizure and finally proved normal by CNS imaging and clinical investigations were enrolled. The peak CSF flow velocity in the cerebral aqueduct of children were 200.02±66.64 ul/s, and the mean net stroke volume is 15.07±17.42 ul/heart beat. Comparing the results in 10 normal adults (5 male, 5 female; 23 to 56 years) with the mean peak velocity of 100.86±18.13ul/s and the net stroke volume of 5.09±0.56, data in children are significantly higher than that in adults. Discussion The value of these flow parameters in children is significantly different from that in adults. Therefore, the age of a patient should be taken into consideration while interpreting these parameters.