Radiological study of the brain at various stages of human immunodeficiency virus infection: early development of brain atrophy

Summary One hundred and one persons infected with human immunodeficiency virus (HIV-1), in whom other central nervous system infections or diseases were excluded, underwent brain CT and/or MRI at various stages of HIV-1 infection: 29 were asymptomatic (ASX), 35 had lymphadenopathy syndrome (LAS), 17 had AIDS-related complex (ARC), and 20 had AIDS. A control group of 32 HIV-1-seronegative healthy persons underwent brain MRI. The most common finding was brain atrophy, found in 9% of controls, and 31% of ASX cases, 29% of LAS, 59% of ARC and 70% of AIDS. Even the difference between the ASX or LAS groups and controls was significant. The changes were bilateral and symmetrical, and they were more severe at later stages of infection. Infratentorial atrophy was seen in the early stages; supratentorial atrophy became more pronounced at ARC, and generalized atrophy was typical of AIDS. Non-specific small hyperintense foci were found on MRI in 13% of controls and 6–15% of the infected groups. Larger, diffuse, bilateral white matter infiltrates were detected in 4 demented patients with AIDS. Four patients with AIDS and 1 with LAS had focal hyperintense lesions in the internal capsules, lentiform nuclei or thalamus, often bilateral on MRI. One patient with AIDS, examined with CT only, had low density in the lentiform nucleus. Loss of brain parenchyma can occur at an early stage of HIV-1 infection, and the atrophic process becomes more intense at later stages (ARC and AIDS). Parenchymal infiltration, seen as hyperintense areas on MRI, is most often associated with severe clinical symptoms, in the later stages of the disease.     

Dynamic imaging of intracranial lesions using fast spin-echo imaging: Differentiation of brain tumors and treatment effects

The purpose of this study was to develop a technique for differentiating between recurrent brain tumors and treatment-related changes, such as radiation necrosis, using dynamic MRI. Ninety-five patients with intracranial mass lesions were evaluated using T1-weighted fast spin-echo (FSE) MRI at 1.5 T. Pathologies included treatment-related changes (n = 32), primary tumors (n = 41), metastatic tumors (n = 5), meningiomas (n = 4), and mixed primary/treatment related changes (n = 13). Signal enhancement-time curves were analyzed by fitting to a sigmoidal-exponential function. Maximal enhancement rates were calculated as the first derivative of the fitted curve. Based on the maximal enhancement rates, treatment-related changes could be differentiated from primary tumors, metastatic tumors, and meningiomas at the P < .05 confidence level. Lesions of mixed tumor and treatment-related change had intermediate values. Dynamic MRI can be used to differentiate treatment-related changes from primary tumors in previously treated patient populations based on maximal enhancement rates. Individual case studies demonstrate the clinical significance of these findings.     

Registration of images from sequential MR studies of the brain

For sequential studies of patients with brain tumors, the authors have designed an automated registration procedure for intra- and interexamination alignment of magnetic resonance images. This was evaluated with artificially misregistered data and data from repeat studies of six healthy volunteers and six brain tumor patients. In a subset of cases, a manual procedure based on matching of neuroanatomic landmarks was also applied for comparison. The results showed that the technique is robust and reproducible, giving an accuracy in the range of 1–2 mm, which corresponded to the spatial resolution of the images. Subject motion between imaging sequences within the same study was negligible, although adjustments (one to two section thicknesses) were required in the z direction to correlate multisection and volume images and to allow accurate image segmentation. For alignment between sequential volunteer and patient examinations, translations of up to 22 mm and rotations in the x, y, and z axes of up to 9° were required. This alignment procedure may be valuable in numerous aspects of treatment planning and patient follow-up.     

Abnormalities of fetal rib number and associated fetal anomalies using three dimensional ultrasonography

Aim

To determine incidence of abnormal number of fetal ribs and its association with other fetal anomalies using 3D ultrasonography.

Materials and methods

A prospective study conducted on 188 singleton pregnant women searching for fetal anomalies including the incidence of abnormal number of fetal ribs and other anomalies. Static 3D volumes with volume contrast imaging using spine map were used. Rendered images were displayed and the ribs were counted.

Results

173 fetuses (92%) were having normal number of ribs. Fifteen fetuses (8%) were found to have abnormal number of ribs; ten fetuses (5.3%) had 11 ribs. On the other hand five fetuses (2.7%) had supernumerary 13 ribs. Eight fetuses (4.2%) were having abnormal number of ribs with no associated anomalies (isolated abnormal number). Seven fetuses (3.7%) in this study had associated anomalies.

Conclusion

Abnormal number of fetal ribs more to be an isolated finding (4.3%) but it may also be seen with other anomalies (3.7% in this study). 3DUS is useful for scanning the fetal ribs in the mid trimester of the pregnancy for early detection of associated genetic aberrations.     

Safety of localizing epilepsy monitoring intracranial electroencephalograph electrodes using MRI: radiofrequency-induced heating

Purpose

To investigate heating during postimplantation localization of intracranial electroencephalograph (EEG) electrodes by MRI.

Materials and Methods

A phantom patient with a realistic arrangement of electrodes was used to simulate tissue heating during MRI. Measurements were performed using 1.5 Tesla (T) and 3T MRI scanners, using head‐ and body‐transmit RF‐coils. Two electrode‐lead configurations were assessed: a “standard” condition with external electrode‐leads physically separated and a “fault” condition with all lead terminations electrically shorted.

Results

Using a head‐transmit–receive coil and a 2.4 W/kg head‐average specific absorption rate (SAR) sequence, at 1.5T the maximum temperature change remained within safe limits (<1°C). Under “standard” conditions, we observed greater heating (≤2.0°C) at 3T on one system and similar heating (<1°C) on a second, compared with the 1.5T system. In all cases these temperature maxima occurred at the grid electrode. In the “fault” condition, larger temperature increases were observed at both field strengths, particularly for the depth electrodes. Conversely, with a body‐transmit coil at 3T significant heating (+6.4°C) was observed (same sequence, 1.2/0.5 W/kg head/body‐average) at the grid electrode under “standard” conditions, substantially exceeding safe limits. These temperature increases neglect perfusion, a major source of heat dissipation in vivo.

Conclusion

MRI for intracranial electrode localization can be performed safely at both 1.5T and 3T provided a head‐transmit coil is used, electrode leads are separated, and scanner‐reported SARs are limited as determined in advance for specific scanner models, RF coils and implant arrangements. Neglecting these restrictions may result in tissue injury. J. Magn. Reson. Imaging 2008;28:1233–1244. © 2008 Wiley‐Liss, Inc.     

Invited. In vivo MRI thermometry using a phase-sensitive sequence: Preliminary experience during MRI-guided laser-induced interstitial thermotherapy of brain tumors

The purpose of this study was the application of the proton-resonance-frequency method to monitor laser-induced interstitial thermotherapy (LITT) in a patient with an astrocytoma WHO II. A phase-sensitive two-dimensional (2D) fast low-angle shot (FLASH) sequence was used to determine the temperature-related phase shifts during LITT. Temperature maps were displayed during therapy with a temporal resolution of 20 seconds. Irradiation was discontinued as soon as the 60 to 65°C isotherm reached the margin of the tumor. A contrast-enhanced MRI study performed immediately after therapy showed a good correlation of the size of an enhancing rim around the lesion with the 60 to 65°C isotherm. The preliminary results of our study indicate that MRI guidance of LITT may be improved by temperature quantification based on the proton-resonance-frequency method.     

多层螺旋CT三维血管成像在颅内动脉瘤夹闭术后随访中的初步应用

目的探讨多层螺旋CT三维血管成像（MS3D-CTA）在颅内动脉瘤夹闭术后随访中的应用价值。方法回顾性分析16例颅内动脉瘤患者夹闭术前后的MS3D-CTA资料。用16层螺旋CT扫描仪获得原始图像，然后采用容积重组（VR）、薄层最大密度投影（MIP）和多平面重组（MPR）技术对图像进行后处理。结果16例颅内动脉瘤夹闭术后复查共发现17个动脉瘤夹，其中后交通动脉瘤6例，前交通动脉瘤5例，大脑中动脉瘤4例，胼周动脉瘤1例2个动脉瘤夹。MS 3D-CTA检查未见异常7例，动脉瘤残留2例，载瘤动脉局限性狭窄4例，伴有血管痉挛3例，所有患者均未见载瘤动脉闭塞及动脉瘤夹滑脱移位征象。VR上12例清晰显示瘤夹及载瘤动脉的三维空间关系，3例较清晰显示，1例胼周动脉瘤使用2个瘤夹者线束硬化性伪影明显而显示较差；动脉瘤夹的形态及大小在薄层MIP与MPR上均能准确显示，但瘤夹与载瘤动脉的三维空间感较差。结论MS3D-CTA是颅内动脉瘤夹闭术后快捷、安全和有效的随访检查手段，VR与薄层MIP、MPR结合可更好地显示颅内动脉瘤夹闭术后改变。     

MR imaging of intracranial hemorrhage in neonates and infants at 2.35 Tesla

Summary The variations of the relative signal intensity and the time dependent changing contrast of intracranial hemorrhages on high-field spin-echo magnetic resonance images (MRI) were studied in 28 pediatric patients. For T1-weighted images, a repetition time (TR) of 500 ms and an echo time (TE) of 30 or 23 ms was used. The corresponding times for T2-weighted images were TR 3000 ms and TE 120 ms. Intracranial hematomas, less than 3 days old, were iso- to mildly hypointense on short TR/TE scans and markedly hypointense on long TR/TE scans (acute stage). In the following four days the signal of the hematomas became hyperintense on short TR/TE scans, beginning in the periphery and proceeding towards the center. On long TR/TE scans the signal remained markedly hypointense (early subacute stage). 7–14 days old hematomas were of high signal intensity on short TR/TE scans. On long TR/TE scans they appeared hypointense in the center and hyperintense in the periphery (late subacute stage). By the end of the second week the hematomas were of high signal intensity on all pulse sequences (chronic stage). Chronic hematomas were surrounded by a parenchymal rim of hypointensity on long TR/TE scans. 28 neonates and infants (with 11 follow-up examinations) of 31.5–70.6 weeks postconceptional age (PCA), with an intracranial hemorrhage were examined. The etiologies of the hemorrhages were: asphyxia (17 cases), brain infarct (2), thrombocytopenia (1), clotting disorder (1) and unknown origin (7). The aim of this study was to describe the appearance of intracranial hemorrhages inneonates and infants with MRI at2.35 Tesla using spine-cho sequences.     

Computer-assisted identification and quantification of multiple sclerosis lesions in MR imaging volumes in the brain

Magnetic resonance (MR) imaging is the principal imaging technique for the diagnosis of multiple sclerosis (MS). However, quantifying the number and extent of lesions on MR images manually is arduous. The authors have developed a computerized three-dimensional (3D) quantitative system to assist in the identification and analysis of MS lesions in proton-density (PD)- and T2-weighted volumes of the head. The system provides intuitive, interactive operations that allow flexible extraction of information from the data. Use of the system to analyze MR examinations of a phantom containing regular “lesions” showed that accurate (average error, <0.21 cm³) and precise (10% or better for lesions > 1 cm³) measurements of objects less than 7 cm³ is possible, and that an estimate of the quantization error predicted the uncertainty in the volume. Analysis of four MR examinations of a chronic-progressive MS patient conducted over an 18-month period was performed. A two-dimensional histogram showing the frequency of voxels with particular PD- and T2-weighted intensities revealed a distinct cluster only in histograms of sections that contained lesions. Measurements and 3D volume rendering of lesions clearly showed changes in lesion shape, position, and size.     

Unsupervised,automated segmentation of the normal brain using a multispectral relaxometric magnetic resonance approach

The purpose of this study was the development and testing of a method for unsupervised, automated brain segmentation. Two spin-echo sequences were used to obtain relaxation rates and proton-density maps from 1.5 T MR studies, with two axial data sets including the entire brain. Fifty normal subjects (age range, 16 to 76 years) were studied. A Three-dimensional (3D) spectrum of the tissue voxels was used for automatic segmentation of gray matter (GM), white matter (WM), and cerebrospinal fluid (CSF) and for calculation of their volumes. Accuracy and reproducibility were tested with a three-compartment phantom simulating GM, WM, and CSF. In the normal subjects, a significant decrease of GM fractional volume and increased CSF volume with age were observed (P < 0.0001), with no significant changes in WM. This multi-spectral segmentation method permits reproducible, operator-independent volumetric measurements.     

Obstructive lesions of the central airways: evaluation by using spiral CT with multiplanar and three-dimensional reformations

The purpose of this study was to assess the accuracy of transverse CT scans as well as multiplanar (MPR) and three-dimensional (3D) reconstructions in the evaluation of obstructive lesions of the central airways. A total of 64 patients were evaluated for the presence of obstructive lesions of the central tracheobronchial tree with transverse spiral CT scans, multiplanar reformations (MPRs), 3D shaded surface displays (3D SSDs) and minimum intensity projections (MIPs). The findings of these modalities were then compared with those obtained at bronchoscopy. The severity, length, and shape of airway narrowing were analyzed comparatively on the four sets of images. Transverse CT scans and MPRs had a similar accuracy (99%) in detecting obstructive airway lesions. The accuracy of both was significantly higher than that of 3DSSDs (90%, p <0.05) and MIPs (81%; p < 0.01). There was no statistically significant difference between the four imaging modalities in the analysis of the morphology of airway stenoses. Symmetric stenoses were similarly analyzed on the four sets of images, whereas MPRs and MIPs failed to depict accurately simple and complex asymmetric stenoses. Transverse CT scans are accurate in the depiction of obstructive lesions of the central airways and may be complemented by MPRs and/or 3DSSDs in their morphologic evaluation.Correspondence to: M. Remy-Jardin     

Intraoperative dynamic MRI: Localization of sites of brain tumor recurrence after high-dose radiotherapy

In patients with malignant astrocytomas or metastatic brain disease treated with high-dose radiotherapy, conventional imaging methods may not adequately distinguish recurrent tumor from radiation change. We used a fast spoiled gradient refocusing technique in the open-configuration intraoperative MR system to assess the rate of regional enhancement of the treated tumor bed and to localize specific sites for pathologic sampling to determine whether gadolinium uptake correlated with histologic data. Twenty-four patients were studied. Fourteen of 15 patients with areas of early enhancement had recurrent tumor present in histologic samples, and 8 of the remaining 9 patients had only reactive changes. Dynamic MRI was predictive of recurrent tumor (P < .0005, Fisher exact test and P < .002, Student t test). We conclude that dynamic MRI in the open-bore magnet is a promising method for localizing potential sites of active tumor growth in patients treated for malignant astrocytomas and metastatic brain lesions.     

Three-dimensional MR imaging and display of intracranial disease: Improvements with the MP-RAGE sequence and gadolinium

Three-dimensional (3D) image rendering was performed in 14 patients who had undergone magnetic resonance (MR) imaging for focal brain lesions. The MR study included the magnetization-prepared rapid gradient-echo (MP-RAGE) sequence with 64 or 128 partitions. Resultant contiguous sections 2.5 or 1.25 mm thick, respectively, were obtained. Images were acquired before and after administration of gadopen-letate dimeglumine. Resultant 3D data sets were processed on a commercially available workstation. Correlative surgical observation was performed in four cases. All data sets were successfully processed into 3D images. The precontrast images proved superior to gadolinium-enhanced images for brain surface rendering. Postcontrast images proved superior for reconstruction of tumors and vascular structures. The 64-partition data set proved sufficient for all postprocessing. Coronal orientation was preferred to sagittal orientation for surface rendering because it provided optimal orthogonal orientation of sulcal and gyral brain surface features. Three-dimensional rendition allowed easy superposition of lesion, brain, vessels, and scalp features-all useful for surgical planning. The central sulcus was easily recognized in the mid-line partitions and traced mediolaterally for projection on the cortical surface. MP-RAGE provides a 3D data set that can be obtained in just over 3 minutes, from which clinically useful 3D renderings are possible. The rapidity of acquisition and capability for 3D rendering provides additional clinical utility.     

Reproducibility of nonparametric feature map segmentation for determination of normal human intracranial volumes with MR imaging data

Semiautomated segmentation of dual-contrast magnetic resonance images was used to determine volumes of total brain, gray matter, white matter, and cerebrospinal fluid (CSF) in healthy volunteers. Reproducibility of the technique was evaluated in terms of intraobserver, interobserver, and study-to-study variations. Intraobserver coefficients of variation ranged from 0.4% to 6.0%, while interobserver values ranged from 0.8% to 9.9%. In both cases, the maximum variations were obtained in volume measurements of tissues with maximum complexity (ie, CSF), and the minimum variation was obtained in determining total brain volume. This was also true in the case of study-to-study variations in volume measurements, for which the coefficients of variation ranged from 0.5% to 8.7%. The use of appropriate preprocessing techniques, which are crucial to the accuracy and reproducibility of the segmentation technique, are described in detail.     

Cognitive impairment after traumatic brain injury: a functional magnetic resonance imaging study using the Stroop task

The anterior cingulate cortex (ACC) plays a key role in cognition, motor function, and emotion processing. However, little is known about how traumatic brain injury (TBI) affects the ACC system. Our purpose was to compare, by functional magnetic resonance imaging (fMRI) studies, the patterns of cortical activation in patients with cognitive impairment after TBI and those of normal subjects. Cortical activation maps of 11 right-handed healthy control subjects and five TBI patients with cognitive impairment were recorded in response to a Stroop task during a block-designed fMRI experiment. Statistical parametric mapping (SPM99) was used for individual subjects and group analysis. In TBI patients and controls, cortical activation, found in similar regions of the frontal, occipital, and parietal lobes, resembled patterns of activation documented in previous neuroimaging studies of the Stroop task in healthy controls. However, the TBI patients showed a relative decrease in ACC activity compared with the controls. Cognitive impairment in TBI patients seems to be associated with alterations in functional cerebral activity, especially less activation of the ACC. These changes are probably the result of destruction of neural networks after diffuse axonal injury and may reflect cortical disinhibition attributable to disconnection or compensation for an inefficient cognitive process.     

腹腔内高压对颅脑创伤患者颅内压的影响

目的 探讨腹腔内高压对颅脑创伤患者颅内压的影响以及腹腔减压术的临床意义.方法对15例同时存在腹部和颅脑创伤的患者腹腔内压力和颅内压监测,比较腹腔减压术后颅内压的变化情况.结果 所有颅脑创伤合并腹部损伤的患者,在行腹腔减压术后,颅内高压均得到一定程度的改善,颅内压下降(15.2±3.6)mm Hg.结论腹腔内压力变化影响颅内压变化,对于颅脑创伤合并腹部损伤的患者,如出现颅内压升高征象,行腹腔减压术可能是一种有效的降低颅内压的于段.     

18F-FDG PET/CT脑显像与EEG用于颞叶癫(癎)灶术前定位

目的 对比研究18F-FDG PET/CT脑显像与EEG对颞叶癫(癎)灶术前定位的价值.方法 回顾性分析临床诊断为颞叶癫(癎)的患者152例,其中男108例,女44例,年龄范围3～59岁.所有患者行18F-FDG PET/CT脑显像和长程和(或)视频EEG检查,其中29例无法准确定位者行颅内电极EEG检查.所有患者行手术治疗,手术切除组织行病理检查,以术后病理为“金标准”,术后随访6个月以上.用x2检验对PET/CT脑显像及长程和(或)视频EEG的准确性进行统计学分析.结果 152例患者PET/CT脑显像定位致(癎)灶的准确性为80.92％ (123/152),长程和(或)视频EEG定位致(癎)灶准确性为43.42％ (66/152),2种检查方法定位致(癎)灶的准确性差异有统计学意义(x2=22.72,P＜0.01),29例术前无法准确定位的患者行颅内电极EEG定位致(癎)灶,其准确性为100％.结论 发作间期18F-FDG PET/CT脑显像定位癫(癎)灶价值优于长程和(或)视频EEG,与颅内电极EEG联合使用,可进一步提高对致(癎)灶定位的准确性.     

Three-dimensionla images of the brain surface from standard CT examination

Three-dimensional (3D) image rendering was performed using data from standard CT examinations of the head. In this new method for 3D imaging of the brain surface interactive image segmentation and integral rendering were combined. Interactive segmentation operations meant that 3D images could be obtained within a short period of time. When combined with integral rendering this permits good-quality 3D views, even when generated from standard thick slices, together with visualisation of both the shape and densities of the brain surface. Surface infarctions can be evaluated in terms of their anatomical localisation to gyri and sulci, thus allowing their relationship to functional areas to be better defined. The technique can be an additional, easily obtainable tool, even in routine practice, for a better understanding of neurological signs. Correspondence to: R. Pozzi Mucelli     

Sonography of congenital malformations of the brain

Summary A variety of congenital malformations of the brain can be diagnosed by cranial sonography. Those which alter macroscopic morphology can be recognized, the findings are similar to those seen on computed tomography and pneumoencephalography. The findings in the Chiari II malformation, agenesis of the corpus callosum, the Dandy-Walker syndrome, holoprosencephaly, lissencephaly, schizencephaly, tuberous sclerosis, and arteriovenous malformations are described in this chapter.     

In vivo validation of tissue segmentation based on a 3D feature map using both a hamster brain tumor model and stereotactically guided biopsy of brain tumors in man

The purpose of this study was to validate our MR tissue segmentation technique using a hamster brain tumor model and malignant brain tumors in man. We used a multispectral tissue segmentation analysis. Three sets of MRI data were included: proton density, T2-weighted fast spin echo, and T1-weighted spin echo, as inputs. Three image preprocessing steps included correcting image nonuniformity, application of an anisotropic diffusion type filter, and data point selection by a qualified observer. We used the k-Nearest Neighbor segmentation algorithm, which does not require prior knowledge of the sample distribution. This choice allowed us to optimize the different tissue clusters present in three-dimensional (3D) feature space. In vivo validation of the technique was performed in hamsters harboring tumors induced with JC virus-transformed HJC-15 cells, as compared to three control animals. Human brain tumors obtained by stereotactically guided biopsy in six patients were also included in the study. Finally, brain tumors were removed from two patients who underwent conventional craniotomy using segmentation-derived images as a guide. In the hamsters, 10 tissues were correctly identified by segmentation and were confirmed histologically (P < .02). In the patients, there was also a strong correlation between our segmentation results and the tissue obtained by stereotactic biopsy (P < .01). In one of the two patients who underwent open craniotomy, segmentation images were useful in revealing tumor spread into vital areas of the brain (motor area). In conclusion, the results of segmentation correlate well with the tissues in vivo and thus warrant further clinical utilization and evaluation.