Source of nonlinearity in echo-time-dependent BOLD fMRI.

Stimulation-induced changes in transverse relaxation rates can provide important insight into underlying physiological changes in blood oxygenation level-dependent (BOLD) contrast. It is often assumed that BOLD fractional signal change (DeltaS/S) is linearly dependent on echo time (TE). This relationship was evaluated at 9.4 T during visual stimulation in cats with gradient-echo (GE) and spin-echo (SE) echo-planar imaging (EPI). The TE dependence of GE DeltaS/S is close to linear in both the parenchyma and large vessel area at the cortical surface for TEs of 6-20 ms. However, this dependence is nonlinear for SE studies in the TE range of 16-70 ms unless a diffusion-weighting of b = 200 s/mm(2) is applied. This behavior is not caused by inflow effects, T(2)* decay during data acquisition in SE-EPI, or extravascular spin density changes. Our results are explained by a two-compartment model in which the extravascular contribution to DeltaS/S vs. TE is linear, while the intravascular contribution can be nonlinear depending on the magnetic field strength and TE. At 9.4 T, the large-vessel IV signal can be minimized by using long TE and/or moderate diffusion weighting. Thus, stimulation-induced relaxation rate changes should be carefully determined, and their physiological meanings should be interpreted with caution.     

Functional magnetic resonance imaging of the human brain based on signal enhancement by extravascular protons (SEEP fMRI).

Functional magnetic resonance imaging (fMRI) studies of the human brain were carried out at 3 Tesla to investigate an fMRI contrast mechanism that does not arise from the blood oxygen-level dependent (BOLD) effect. This contrast mechanism, signal enhancement by extravascular protons (SEEP), involves only proton-density changes and was recently demonstrated to contribute to fMRI signal changes in the spinal cord. In the present study it is hypothesized that SEEP fMRI can be used to identify areas of neuronal activity in the brain with as much sensitivity and precision as can be achieved with BOLD fMRI. A detailed analysis of the areas of activity, signal intensity time courses, and the contrast-to-noise ratio (CNR), is also presented and compared with the BOLD fMRI results. Experiments were carried out with subjects performing a simple finger-touching task, or observing an alternating checkerboard pattern. Data were acquired using a conventional BOLD fMRI method (gradient-echo (GE) EPI, TE = 30 ms), a conventional method with reduced BOLD sensitivity (GE-EPI, TE = 12 ms), and SEEP fMRI (spin-echo (SE) EPI, TE = 22 ms). The results of this study demonstrate that SEEP fMRI may provide better spatial localization of areas of neuronal activity, and a higher CNR than conventional BOLD fMRI, and has the added benefit of lower sensitivity to field inhomogeneities.     

Sources of functional apparent diffusion coefficient changes investigated by diffusion-weighted spin-echo fMRI.

The mechanism behind previously observed changes in the apparent diffusion coefficient (ADC) during brain activation is not well understood. Therefore, we investigated the signal source and spatial specificity of functional magnetic resonance imaging (fMRI) ADC changes systematically in the visual cortex of cats using diffusion-weighted (DW) spin-echo (SE) fMRI with b-values of 2, 200, and 800 s/mm(2), and echo times (TE) of 16, 28, and 60 ms at 9.4 T. For b > or = 200 s/mm(2), no ADC changes were detected in brain parenchyma, suggesting a minimal tissue contribution to the ADC change. For b < or = 200 s/mm(2), TE-dependent ADC increases were observed. When the venous blood contribution was minimized, the ADC change was higher at the middle cortical layer than at the cortical surface, which is mainly attributed to a functional elevation in arterial blood volume. At TE = 16 ms, the highest ADC changes occurred at the cortical surface with its large draining veins, which can mainly be explained by an additional contribution from the venous blood oxygenation changes. Our TE-dependent ADC results agree with computer simulations based on a three-compartment model. The contribution of arterial blood volume changes in ADC fMRI offers an improvement in spatial localization for SE-BOLD fMRI studies.     

Hepatic malignant tumour versus cavernous haemangioma: differentiation on multiple breath-hold turbo spin-echo MRI sequences with different T2-weighting and T2-relaxation time measurements on a single slice multi-echo sequence

AIM: We evaluated the signal intensity change on breath-hold turbo spin-echo (TSE) T2-weighted sequences using different echo times (TE) and T2-relaxation time measurements on a single slice eight-echo sequence in the differentiation of hepatic malignancy from cavernous haemangioma. MATERIALS AND METHODS: Breath-hold TSE T2-weighted axial images of the liver were performed at TEs of 80, 120 and 160 ms in 34 patients with focal liver lesions (13 with cavernous haemangiomas, 14 with hepatocellular carcinomas and seven with metastases). The lesion percentage signal intensity change on the lower TE image to the higher TE image was calculated. T2-relaxation time was measured on a single slice eight-echo sequence. RESULTS: The TE pair 80/160 ms on breath-hold TSE T2-weighted sequences gave a performance (100% sensitivity, 92% specificity, 95% positive predictive value and 100% negative predictive value) better than other TE pairs in differentiating haemangioma from malignancy. Addition of fat-suppression compromised the diagnostic performance for all TE-pairs. The use of T2 relaxation time threshold of < 112 ms as indicative of malignant lesion achieved a 100% sensitivity, 77% specificity, 88% positive predictive value and 100% negative predictive value. CONCLUSION: Percentage signal intensity change on breath-hold TSE T2-weighted sequences at TE 80/160 ms appears to be a quick and potentially useful means of differentiating hepatic malignancy from haemangioma.     

Flow velocity of the cortical vein and its effect on functional brain MRI at 1.5t: Preliminary results by Cine-MR venography

The purpose of this study is to demonstrate the effect of altering flow velocity of cerebral cortical veins as the source of the signal change observed in functional magnetic resonance imaging (fMRI) of the brain. 10 healthy volunteers were examined after instructions in self-paced hand grasping. Experiments were performed using a 1.5-Tesla whole body MR scanner with a conventional two-dimensional gradient echo sequence (TR/TE/flip angle 400/60/40, first order flow rephased, reduced band width 8 Hz/pixel). Flow velocity measurements were performed for the cortical veins which corresponded to the activated areas depicted on fMRI. Velocity was estimated from the cine-MR venography (cine-MRV) with a tagging technique. Flow phantom studies were performed to delineate the effect of flow velocity differences upon the subtraction images of fMRI. The cine-MRV revealed increased flow velocity of the cortical veins during activation in seven volunteers, with a mean velocity difference of 15 mm/sec. Flow phantom studies suggested that the increased flow velocity may result in changes of the flow signal profile due to oblique flow displacement. Subtraction of the two images with different flow profiles produces flow signal enhancement. Increased flow velocity of the cortical veins during the activation is an important factor which contributes to the signal of fMRI.     

Functional magnetic resonance imaging of the human lumbar spinal cord

PURPOSE: To determine whether consistent regions of activity could be observed in the lumbar spinal cord of single subjects with spin-echo functional MRI (fMRI) if several repeated experiments were performed within a single imaging session. MATERIALS AND METHODS: Repeated fMRI experiments of the human lumbar spinal cord were performed at 1.5 T with a single-shot spin-echo technique (half-Fourier single-shot turbo spin-echo (HASTE)) as used by previous investigators, and a modified method (fluid-attenuated inversion recovery (FLAIR)-HASTE) that nulled the otherwise highly variable signal from the cerebrospinal fluid (CSF). RESULTS: FLAIR-HASTE reduced the variability of the signal in the CSF region to background levels, and presumably reduced associated artifacts in the spinal cord. Consistent areas of activation in the spinal cord in response to a thermal stimulus just below the knee were not observed across the fMRI experiments with either method. CONCLUSION: FLAIR-HASTE was useful for removing artifact in the spinal cord signal induced by variability in the CSF signal. However, with the techniques used in this study, we were not able to confirm the presence of a consistent fMRI response in the lumbar spinal cord because of the signal enhancement by extravascular protons (SEEP) effect during thermal stimulation of the hindlimb.     

血管外质子信号增强颈髓功能成像序列参数优化

目的通过优化成像参数,获得一种较高质量的利用血管外质子信号增强的颈髓功能成像。方法采用GRE-echoplan序列中的一种新的血管外质子信号增强(SEEP)磁共振功能成像技术,按TR、TE时间的相关关系,通过固定TR改变TE,同时通过选择使用呼吸门控或心电门控,是否加饱和带等不同参数下获得颈髓功能成像,比较上述不同参数下颈髓fMRI成像的影像质量,包括信噪比、显示激活区部位是否清晰、确定,是否可重复。结果采用SEEP成像技术能实现颈髓功能成像,TR 1065s与TE 45s时能获得较高质量的颈髓功能成像,使用心电门控较不使用心电门控图像质量明显提高,加前饱和带可减少呼吸与吞咽所致的伪影,呼吸门控对图像质量无明显影响。结论 GRE-echo plan序列的SEEP成像技术经优化技术参数后能获得较高质量的颈髓功能成像。     

Single-shot echo-planar imaging of multiple sclerosis: effects of varying echo time

Our aim was to determine the relative merits of short and long echo times (TE) with single-shot echo-planar imaging for imaging cerebral lesions such as multiple sclerosis. We examined seven patients with clinically definite multiple sclerosis were imaged at 1.5 T. Patients were scanned with spin-echo, single-shot echo-planar imaging, using TEs of 45, 75, 105, and 135 ms. Region of interest (ROI) measurements were performed on 36 lesions at or above the level of the corona radiata. The mean image contrast (IC) was highest (231.1) for a TE of 45 ms, followed by 75 ms (218.9), 105 ms (217.9), and 135 ms (191.6). When mean contrast-to-noise ratios (C/N) were compared, the value was again highest (29.7) for TE 45 ms, followed by 75 ms (28.9), 105 ms (28.5), and 135 ms (26.3). In a lesion-by-lesion comparison, TE 45 ms had the highest IC and C/N in the largest number of cases (50 % and 47.2 %, respectively). IC and C/N for TE 45 ms were superior to those of 75 ms in 64 % and 58 %, respectively. These results support the use of relatively short TEs for single-shot echo-planar imaging in the setting of cerebral lesions such as multiple sclerosis. Received: 30 December 1997 Accepted: 19 June 1998     

3T 1H-MR spectroscopy in grading of cerebral gliomas: comparison of short and intermediate echo time sequences

BACKGROUND AND PURPOSE: Echo time (TE) can have a large influence on the spectra in proton MR spectroscopy ((1)H-MR spectroscopy). The purpose of this study was to comparatively assess the diagnostic value of 3T single-voxel (1)H-MR spectroscopy with short or intermediate TEs in grading cerebral gliomas. METHODS: Single voxel (1)H-MR spectroscopy was performed at 3T in 35 patients with cerebral glioma. The spectra were obtained with both short (35 ms) and intermediate TEs (144 ms). Metabolite ratios of choline (Cho)/creatine (Cr), Cho/N-acetylaspartate (NAA), lipid and lactate (LL)/Cr and myo-inositol (mIns)/Cr were calculated and compared between short and intermediate TEs in each grade. After receiver operating characteristic curve analysis, diagnostic accuracy for each TE in differentiating high-grade glioma from low-grade glioma was compared. RESULTS: At short TE, Cho/Cr and Cho/NAA ratios were significantly lower, and LL/Cr and mIns/Cr were significantly higher, compared with those at intermediate TE, regardless of tumor grade. Lactate inversion at intermediate TE was found in only 2 patients. At both TEs, there were significant differences in Cho/Cr and LL/Cr ratios between low- and high-grade gliomas. Diagnostic accuracy was slightly higher at short TE alone or combined with intermediate TE than intermediate TE alone (85.7% versus 82.9%). CONCLUSION: Metabolite ratios were significantly different between short and intermediate TE. Cho/Cr and LL/Cr ratios at either TE were similarly useful in differentiating high-grade gliomas from low-grade gliomas. If only a single spectroscopic sequence can be acquired, short TE seems preferable because of poor lactate inversion at intermediate TE on 3T single-voxel (1)H-MR spectroscopy.     

Functional MRI of the cervical spinal cord on 1.5 T with fingertapping: to what extent is it feasible?

Introduction Until recently, functional magnetic resonance imaging (fMRI) with blood oxygen level-dependent (BOLD) contrast, was mainly used to study brain physiology. The activation signal measured with fMRI is based upon the changes in the concentration of deoxyhaemoglobin that arise from an increase in blood flow in the vicinity of neuronal firing. Technical limitations have impeded such research in the human cervical spinal cord. The purpose of this investigation was to determine whether a reliable fMRI signal can be elicited from the cervical spinal cord during fingertapping, a complex motor activity. Furthermore, we wanted to determine whether the fMRI signal could be spatially localized to the particular neuroanatomical location specific for this task. Methods A group of 12 right-handed healthy volunteers performed the complex motor task of fingertapping with their right hand. T2*-weighted gradient-echo echo-planar imaging on a 1.5-T clinical unit was used to image the cervical spinal cord. Motion correction was applied. Cord activation was measured in the transverse imaging plane, between the spinal cord levels C5 and T1. Results In all subjects spinal cord responses were found, and in most of them on the left and the right side. The distribution of the activation response showed important variations between the subjects. While regions of activation were distributed throughout the spinal cord, concentrated activity was found at the anatomical location of expected motor innervation, namely nerve root C8, in 6 of the 12 subjects. Conclusion fMRI of the human cervical spinal cord on an 1.5-T unit detects neuronal activity related to a complex motor task. The location of the neuronal activation (spinal cord segment C5 through T1 with a peak on C8) corresponds to the craniocaudal anatomical location of the neurons that activate the muscles in use.     

Comparison of the dependence of blood R2 and R2* on oxygen saturation at 1.5 and 4.7 Tesla.

Gradient-echo (GRE) blood oxygen level-dependent (BOLD) effects have both intra- and extravascular contributions. To better understand the intravascular contribution in quantitative terms, the spin-echo (SE) and GRE transverse relaxation rates, R(2) and R(2)(*), of isolated blood were measured as a function of oxygenation in a perfusion system. Over the normal oxygenation saturation range of blood between veins, capillaries, and arteries, the difference between these rates, R'(2) = R(2)(*) - R(2), ranged from 1.5 to 2.1 Hz at 1.5 T and from 26 to 36 Hz at 4.7 T. The blood data were used to calculate the expected intravascular BOLD effects for physiological oxygenation changes that are typical during visual activation. This modeling showed that intravascular DeltaR(2)(*) is caused mainly by R(2) relaxation changes, namely 85% and 78% at 1.5T and 4.7T, respectively. The simulations also show that at longer TEs (>70 ms), the intravascular contribution to the percentual BOLD change is smaller at high field than at low field, especially for GRE experiments. At shorter TE values, the opposite is the case. For pure parenchyma, the intravascular BOLD signal changes originate predominantly from venules for all TEs at low field and for short TEs at high field. At longer TEs at high field, the capillary contribution dominates. The possible influence of partial volume contributions with large vessels was also simulated, showing large (two- to threefold) increases in the total intravascular BOLD effect for both GRE and SE.     

Quantitative and qualitative assessment of reactive hematopoietic bone marrow in aplastic anemia using MR spectroscopy with variable echo times

OBJECTIVE: To assess quantitative and qualitative differences in water components between normal bone marrow and reactive hematopoietic marrow in aplastic anemia using magnetic resonance (MR) spectroscopy with variable echo times (TEs). DESIGN: Water content, T2 value of the water component, and signal change in water related to TE were assessed in normal bone marrow and reactive hematopoietic bone marrow by a stimulated echo acquisition mode with TEs of 30, 45, 60, and 90 ms. PATIENTS: Six patients with aplastic anemia (13-84 years) and seven normal volunteers (25-38 years) were examined. RESULTS AND CONCLUSION: Reactive hematopoietic marrow showed significantly higher water content than normal bone marrow. The T2 value of water components tended to be longer in reactive hematopoietic marrow. Water signal ratio related to TE was significantly higher in reactive hematopoietic marrow. These results suggest a quantitative and qualitative difference in water components between normal and reactive hematopoietic bone marrow.     

Physiological origin of low‐frequency drift in blood oxygen level dependent (BOLD) functional magnetic resonance imaging (fMRI)

We investigated the biophysical mechanism of low‐frequency drift in blood‐oxygen‐level‐dependent (BOLD) functional magnetic resonance imaging (fMRI) (0.00–0.01 Hz), by exploring its spatial distribution, dependence on imaging parameters, and relationship with task‐induced brain activation. Cardiac and respiratory signals were concurrently recorded during MRI scanning and subsequently removed from MRI data. It was found that the spatial distribution of low‐frequency drifts in human brain followed a tissue‐specific pattern, with greater drift magnitude in the gray matter than in white matter. In gray matter, the dependence of drift magnitudes on TE was similar to that of task‐induced BOLD signal changes, i.e., the absolute drift magnitude reached the maximum when TE approached T whereas relative drift magnitude increased linearly with TE. By systematically varying the flip angle, it was found that drift magnitudes possessed a positive dependence on image intensity. In phantom experiments, the observed drift was not only much smaller than that of human brain, but also showed different dependence on TE and flip angle. In fMRI studies with visual stimulation, a strong positive correlation between drift effects at baseline and task‐induced BOLD signal changes was observed both across subjects and across activated pixels within individual participants. We further demonstrated that intrinsic, physiological drift effects are a major component of the spontaneous fluctuations of BOLD fMRI signal within the frequency range of 0.0–0.1 Hz. Our study supports brain physiology, as opposed to scanner instabilities or cardiac/respiratory pulsations, as the main source of low‐frequency drifts in BOLD fMRI. Magn Reson Med 61, 2009. © 2009 Wiley‐Liss, Inc.     

High-resolution fMRI using multislice partial k-space GR-EPI with cubic voxels.

The premises of this work are: 1) the limit of spatial resolution in fMRI is determined by anatomy of the microcirculation; 2) because of cortical gray matter tortuosity, fMRI experiments should (in principle) be carried out using cubic voxels; and 3) the noise in fMRI experiments is dominated by low-frequency BOLD fluctuations that are a consequence of spontaneous neuronal events and are pixel-wise dependent. A new model is proposed for fMRI contrast which predicts that the contrast-to-noise ratio (CNR) tends to be independent of voxel dimensions (in the absence of partial voluming of activated tissue), TE, and scanner bandwidth. These predictions have been tested at 3 T, and results support the model. Scatter plots of fMRI signal intensities and low-frequency fluctuations for activated pixels in a finger-tapping paradigm demonstrated a linear relationship between signal and noise that was independent of TE. The R(2) value was about 0.9 across eight subjects studied. The CNR tended to be constant across pixels within a subject but varied across subjects: CNR = 3.2 +/- 1.0. fMRI statistics at 20- and 40-ms TE values were indistinguishable, and TE values as short as 10 ms were used successfully. Robust fMRI data were obtained across all subjects using 1 x 1 x 1 mm(3) cubic voxels with 10 contiguous slices, although 1.5 x 1.5 x 1.5 mm(3) was found to be optimum. Magn Reson Med 46:114-125, 2001.     

Hematopoietic bone marrow in the adult knee: spin-echo and opposed-phase gradient-echo MR imaging

Hematopoietic bone marrow in the distal femur of the adult may be mistaken for a pathologic marrow process in magnetic resonance imaging of the knee. We investigated the incidence of hematopoietic marrow in the distal femur in a series of 51 adult patients and compared spin-echo (TR/TE in ms: 500/35, 2000/80) and opposed-phase gradient-echo (0.35 T, TR/TE in ms: 1000/30, = 75°) magnetic resonance images. Zones with intermediate to low signal intensity on T1-weighted spinecho and opposed-phase gradient-echo sequences representing hematopoietic marrow within high signal intensity fatty marrow were observed in 18 of the 51 patients. Five patterns of marrow signal reduction were identified; type 0: uniform high signal, i.e., no signal change; type I, focal signal loss; type II, multifocal signal loss without confluence; type III, confluent signal loss; and type IV, complete homogeneous reduction in marrow signal. Opposed-phase gradient-echo sequences demonstrated markedly greater red-yellow marrow contrast than conventional spin-echo sequences. Follow-up studies in three patients using a gradient-echo sequence with TE varying from 10 to 21 ms at 1-ms increments showed a cyclic increase and decrease in red and yellow marrow signal intensity depending on the TE. The contribution of intravoxel chemical shift effects on red-yellow marrow contrast in opposed-phase gradient-echo images was verified by almost complete cancellation of the TE-dependent marrow signal oscillation with use of a chemically selective pulse presaturating the water protons.Hematopoietic marrow in the adult distal femur in the absence of hematologic abnormalities is found primarily in women of menstruating age. It may be residual and may represent a biologic variation in the normal adult pattern of red-yellow marrow distribution. Reconverted red marrow appears to be related to increased erythrocyte demand. Residual and reconverted red marrow should not be mistaken for bone marrow malignancy. Opposed-phase gradient-echo imaging is easily implemented and appears ideally suited to monitor the distribution of hematopoietic marrow as a function of age and erythrocyte demand in vivo.     

Theoretical noise model for oxygenation-sensitive magnetic resonance imaging.

Contrast-to-noise ratio (CNR) in blood oxygenation level-dependent (BOLD) based functional MRI (fMRI) studies is a fundamental parameter to determine statistical significance and therefore to map functional activation in the brain. The CNR is defined here as BOLD contrast with respect to temporal fluctuation. In this study, a theoretical noise model based on oxygenation-sensitive MRI signal formation is proposed. No matter what the noise sources may be in the signal acquired by a gradient-echo echo-planar imaging pulse sequence, there are only three noise elements: apparent spin density fluctuations, S(0)(t); transverse relaxation rate fluctuations, R(2) (*)(t); and thermal noise, n(t). The noise contributions from S(0)(t), R(2) (*)(t), and n(t) to voxel time course fluctuations were evaluated as a function of echo time (TE) at 3 T. Both noise contributions caused by S(0)(t) and R(2) (*)(t) are significantly larger than that of thermal noise when TE = 30 ms. In addition, the fluctuations between S(0)(t) and R(2) (*)(t) are cross-correlated and become a noise factor that is large enough and cannot be ignored. The experimentally measured TE dependences of noise, temporal signal-to-noise ratio, and BOLD CNR in finger-tapping activation regions were consistent with the proposed model. Furthermore, the proposed theoretical models not only unified previously proposed BOLD CNR models, but also provided mechanisms for interpreting apparent controversies and limitations that exist in the literature.     

T2* and proton density measurement of normal human lung parenchyma using submillisecond echo time gradient echo magnetic resonance imaging.

OBJECTIVE: To obtain T2* and proton density measurements of normal human lung parenchyma in vivo using submillisecond echo time (TE) gradient echo (GRE) magnetic resonance (MR) imaging. MATERIALS AND METHODS: Six normal volunteers were scanned using a 1.5-T system equipped with a prototype enhanced gradient (GE Signa, Waukausha, WI). Images were obtained during breath-holding with acquisition times of 7-16 s. Multiple TEs ranging from 0.7 to 2.5 ms were tested. Linear regression was performed on the logarithmic plots of signal intensity versus TE, yielding measurements of T2* and proton density relative to chest wall muscle. Measurements in supine and prone position were compared, and effects of the level of lung inflation on lung signal were also evaluated. RESULTS: The signal from the lung parenchyma diminished exponentially with prolongation of TE. The measured T2* in six normal volunteers ranged from 0.89 to 2.18 ms (1.43 +/- 0.41 ms, mean +/- S.D.). The measured relative proton density values ranged between 0.21 and 0.45 (0.29 +/- 0.08, mean +/- S.D.). Calculated T2* values of 1.46 +/- 0.50, 1.01 +/- 0.29 and 1.52 +/- 0.18 ms, and calculated relative proton densities of 0.20 +/- 0.03, 0.32 +/- 0.13 and 0.35 +/- 0.10 were obtained from the anterior, middle and posterior portions of the supine right lung, respectively. The anterior-posterior proton density gradient was reversed in the prone position. There was a pronounced increase in signal from lung parenchyma at maximum expiration compared with maximum inspiration. The ultrashort TE GRE technique yielded images demonstrating signal from lung parenchyma with minimal motion-induced noise. CONCLUSION: Quantitative in vivo measurements of lung T2* and relative proton density in conjunction with high-signal parenchymal images can be obtained using a set of very rapid breath-hold images with a recently developed ultrashort TE GRE sequence.     

An improved method for spinal functional MRI with large volume coverage of the spinal cord

PURPOSE: To develop a spinal functional MRI (fMRI) method with three-dimensional coverage of a large extent of the spinal cord with minimal partial volume effects MATERIALS AND METHODS: fMRI data of the cervical spinal cord were obtained at 1.5 T with a single-shot fast spin-echo imaging method, from thin contiguous sagittal slices spanning the cord. Thermal stimulation was applied to the palm of the hand in a block pattern with 15 degrees C for stimulation and 32 degrees C during baseline periods. Prior to analysis, the image data at each time point were reformatted into three-dimensional volumes and resliced perfectly transverse to the spinal cord. Smoothing was applied only in the superior-inferior (S/I) direction across uniform tissue types. Active voxels were then identified by means of a correlation to a model paradigm. RESULTS: The resulting activity maps demonstrate activity primarily in ipsilateral sensory areas and in some motor areas, consistent with the spinal cord neuroanatomy. These data also demonstrate detail of the subsegmental organization of the spinal cord, as well as anatomical detail of the spinous processes and positions of nerve roots. CONCLUSION: The spinal fMRI method described enables large volume coverage of the spinal cord in three dimensions, with reliable and reproducible results.     

MR灌注成像的回波时间和对比剂剂量的选择

目的　研究回波时间 (TE)和对比剂剂量对MR灌注成像 (PWI)的图像质量和计算参数的影响作用 ,确定二者的最适值。方法　 35例健康志愿者 ,分别以TE =2 0、30、4 0ms和 0 1、0 2mmol/kg的钆喷替酸葡甲胺 (Gd DTPA)及TE =30ms、0 3mmol/kg的对比剂行PWI ,观察PWI图像的质量 ,计算脑白质的最大信号强度下降百分率 (SRRmax)和平均通过时间 (MTT)。结果　未用对比剂的PWI图像 ,TE =2 0、30、4 0ms时各组间脑白质信噪比差异有显著意义 (q2 0ms,3 0ms=18 3,q2 0ms,40ms=2 5 9,q3 0ms,40ms=7 5 ,P <0 0 1)。剂量相同或TE相同时各组白质的SRRmax间差异有显著意义 (F0 1mmol/kg=31 5 ,F0 2mmol/kg=131 5 ,F2 0ms=12 1 9,F3 0ms=4 6 9,F40ms=91 4 ,P <0 0 1) ,但MTT间差异无显著意义 (F =0 0 9,P >0 0 5 )。对比剂剂量为 0 3mmol/kg、TE =30ms时与 0 2mmol/kg、TE =30ms方案相比SRRmax差异无显著意义 (F =0 91,P >0 0 5 ) ,而MTT则差异有显著意义 (F =10 2 ,P <0 0 5 )。结论　TE =30ms和 0 2mmol/kg的对比剂剂量 ,可获得最优化的PWI结果