MRI-guided, open trial of abciximab for ischemic stroke within a 3- to 24-hour window.

The authors assessed the effect of IV abciximab on early neurologic improvement and ischemic lesion growth in 29 patients with supratentorial stroke and NIH stroke scale score (NIHSSS) > or = 4 (11.1 +/- 5.9), treated within 3 to 24 (13.6 +/- 5.5) hours of onset. The 48 to 72-hour NIHSSS improvement was 4.4 +/- 3.2 and the 24-hour lesion growth on DWI was +23% (-50%, +103%); 7/26 (27%) patients experienced lesion size decrease. Treatment of sub-24-hour stroke with abciximab improves early post-treatment neurologic status and often attenuates ischemic lesion growth.

Correlation between magnetic resonance spectroscopy imaging and image-guided biopsies: semiquantitative and qualitative histopathological analyses of patients with untreated glioma.

OBJECTIVE: Since intratumoral heterogeneity of gliomas is not adequately reflected in conventional magnetic resonance imaging (MRI), we sought to determine a correlation between different proton magnetic resonance spectroscopic imaging ((1)H MRSI) metabolic ratios and the degree of tumor infiltration in diffusely infiltrating gliomas. In this report, we describe the microscopic anatomy of gliomas on imaging. METHODS: Image-guided biopsies with semiquantitative and qualitative histopathological analyses from a series of 31 untreated patients with low- and high-grade gliomas were correlated with multivoxel (1)H MRSI referenced to the same spatial coordinates. RESULTS: This series yielded 247 tissue samples and 307 observations. Choline-containing compounds using contralateral creatine and choline for normalization or ipsilateral N-acetylaspartate appear to correlate best with the degree of tumor infiltration. Similar correlations were present within each grade after stratification. Despite the interpatient overlap of metabolic ratios between normal tissue and mild tumor infiltration, preliminary analyses revealed that (1)H MRSI appears more accurate than conventional MRI in defining the tumor boundary and quantifying the degree of tumor infiltration. CONCLUSION: This is the first study showing histopathological validation of tumor boundaries using (1)H MRSI. These results support the conclusion that (1)H MRSI accurately reflects the extent of the disease in patients with gliomas. This has important diagnostic and therapeutic implications for more accurately assessing the burden of disease as well as for planning and assessing response to therapy.

Single-voxel proton MRS of the human brain at 1.5T and 3.0T.

Single-voxel proton spectra of the human brain were recorded in five subjects at both 1.5T and 3.0T using the STEAM pulse sequence. Data acquisition parameters were closely matched between the two field strengths. Spectra were recorded in the white matter of the centrum semiovale and in phantoms. Spectra were compared in terms of resolution and signal-to-noise ratio (SNR), and transverse relaxation times (T(2)) were estimated at both field strengths. Spectra at 3T demonstrated a 20% improvement in sensitivity compared to 1.5T at short echo times (TE = 20 msec), which was lower than the theoretical 100% improvement. Spectra at long echo times (TE = 272 msec) exhibited similar SNR at both field strengths. T(2) relaxation times were almost twofold shorter at the higher field strength. Spectra in phantoms demonstrated significantly improved resolution at 3T compared to 1.5T, but resolution improvements in in vivo spectra were almost completely offset by increased linewidths at higher field.

MR spectroscopy study of dichloroacetate treatment after ischemic stroke.

In a double-blind, placebo-controlled study, we used 1H MR spectroscopy to assess the effect of a single infusion of sodium dichloroacetate on lesion lactate 1 to 5 days after ischemic stroke. Apparent trends toward a reduction in lactate/N-acetyl compound ratios were seen at the higher drug doses employed, and in patients treated in the first 2 days following infarction. Use of spectroscopic measures as endpoints is feasible in acute stroke clinical trials.

Premature partial closure and other deformities of the growth plate: MR imaging and three-dimensional modeling.

PURPOSE: To examine growth plates of the distal femur and tibia with magnetic resonance (MR) imaging to detect bone bridges and other deformities in children. MATERIALS AND METHODS: Thirteen children (nine boys and four girls, aged 5-13 years; mean age, 9.8 years) were referred because of suspected or known bone bridging of the growth plate. Among the 13 patients, 10 had Salter-Harris fractures of the knee or ankle, two had Blount disease, and one had neonatal sepsis. Fat-saturated spoiled gradient-recalled images enabled reconstruction of a three-dimensional model of the growth plate. Patients underwent one to four MR examinations. RESULTS: Nine patients had bone bridging of less than 1% to 39% of the area of the growth plate. On MR images obtained in the growth plate of five patients, a stripe of low signal intensity indicated fracture. On MR images obtained in three patients, intrusions of growth plate cartilage into the metaphysis were seen to increase in depth over time. MR images obtained in four patients showed no bridges. In the two patients who underwent surgery, excellent correspondence was found between MR findings and surgical observations. CONCLUSION: Marked undulation or splitting of the growth plate may occur with fixation of some cartilage in the metaphysis or epiphysis while growth continues. The configuration of the growth plate and bone bridges can be accurately mapped with MR imaging. Treatment planning is facilitated.

Time course of ADCw changes in ischemic stroke: beyond the human eye!

BACKGROUND AND PURPOSE: Using newly developed computerized image analysis, we studied the heterogeneity of apparent diffusion coefficient of water (ADCw) values in human ischemic stroke within 10 hours of onset. METHODS: Echo-planar trace diffusion-weighted images from 9 patients with focal cortical ischemic stroke were obtained within 10 hours of symptom onset. An Iterative Self-Organizing Data Analysis (ISODATA) clustering algorithm was implemented to segment different tissue types with a series of DW images. ADCw maps were calculated from 4 DW images on a pixel-by-pixel basis. The segmented zones within the lesion were characterized as low, pseudonormal, or high, expressed as a ratio of the mean+/-SD of ADCw of contralateral noninvolved tissue. RESULTS: The average ADCW in the ischemic stroke region within 10 hours of onset was significantly depressed compared with homologous contralateral tissue (626.6+/-76.8 versus 842.9+/-60.4x10(-6) mm2/s; P<0.0001). Nevertheless, ISODATA segmentation yielded multiple zones within the stroke region that were characterized as low, pseudonormal, and high. The mean proportion of low:pseudonormal:high was 72%:20%:8%. CONCLUSIONS: Despite low average ADCW, computer-assisted segmentation of DW MRI detected heterogeneous zones within ischemic lesions corresponding to low, pseudonormal, and high ADCw not visible to the human eye. This supports acute elevation of ADCw in human ischemic stroke and, accordingly, different temporal rates of tissue evolution toward infarction.

Cerebral tumor volume calculations using planimetric and eigenimage analysis.

Volume determination in cerebral tumors requires accurate and reproducible segmentation. This task has been traditionally accomplished using planimetric methods which define the boundary of the lesion using thresholding and edge detection schemes. These methods lack accuracy and reproducibility when the contrast between the lesion and surrounding tissue is not maximized. Because of this limitation contrast agents are used providing reproducible results for the enhancing portion of the lesion. A novel approach for volume determination has been developed (eigenimage filter) which segments a desired feature (tissue type) from surrounding undesired features in a sequence of images. This method corrects for partial volume effects and has been shown to provide accurate and reproducible volume determinations. In addition, the eigenimage filter does not require the use of contrast and has the capability to segment a lesion into multiple regions. This allows different components of the lesion to be included and monitored in treatment. In this study planimetric methods and the eigenimage filter were compared for segmenting cerebral tumors and determining their volumes. The planimetric methods were reproducible in determining volumes for the enhancing portion of the lesion with interobserver percent differences < 8% and intraobserver percent differences < 4%. The eigenimage filter had interobserver percent differences < 7% and intraobserver percent differences < 3%. In the eigenimage procedure both the enhancing portion of the lesion as well as additional regions within the lesion were identified. Comparing the results obtained from the two methods demonstrated good agreement for presurgical studies (percent differences < 9%). When comparing postsurgical studies large differences were seen. In the postsurgical studies the eigenimage method allowed multiple regions to be followed in subsequent MRI and in two patients showed a volume change that suggested tumor recurrence more clearly. Since the amount of information obtained using the eigenimage filter may allow a more complete assessment of the lesion, it is suggested that it could improve the clinical evaluation of cerebral tumors.

Segmentation of MRS signals using ASPECT (analysis of SPectra using Eigenvector Decomposition of Targets).

Efforts to minimize the effects of partial volume contamination (PVC) in in vivo magnetic resonance spectroscopy (MRS) have focused upon improving the sensitivity and efficiency of spatially localized MRS measurements. Such improvements may improve spatial resolution and reduce the time required to acquire multiple spectra, however, PVC can affect in vivo spectra at any resolution. In this paper, a model for segmenting in vivo MRS signals compromised by PVC in selected applications is introduced. The segmentation algorithm used is linear and is based on filters originally developed for image processing applications. The model is developed from first principles and evaluated using computer simulations. It is suited for segmenting multivoxel or chemical shift imaging data, and can be used with spectra acquired at any spatial resolution. It is used to estimate the size of the partial volumes contributing to a voxel compromised by PVC and the spatially selective signal components that would be expected to arise from these partial volumes if they could be measured directly. Several spectral perturbants present in in vivo MRS measurements violate the linearity assumptions underlying the model and produce systematic errors that must be accounted for. A number of perturbants are discussed, and the potential in vivo applications of the model are illustrated using solvent-suppressed 1H-CSI spectra from the normal human brain.

Optimization of MRI protocols and pulse sequence parameters for eigenimage filtering.

The eigenimage filter generates a composite image in which a desired feature is segmented from interfering features. The signal-to-noise ratio (SNR) of the eigenimage equals its contrast-to-noise ratio (CNR) and is directly proportional to the dissimilarity between the desired and interfering features. Since image gray levels are analytical functions of magnetic resonance imaging (MRI) parameters, it is possible to maximize this dissimilarity by optimizing these parameters. For optimization, the authors consider four MRI pulse sequences: multiple spin-echo (MSE); spin-echo (SE); inversion recovery (IR); and gradient-echo (GE). The authors use the mathematical expressions for MRI signals along with intrinsic tissue parameters to express the objective function (normalized SNR of the eigenimage) in terms of MRI parameters. The objective function along with a set of diagnostic or instrumental constraints define a multidimensional nonlinear constrained optimization problem, which the authors solve by the fixed point approach. The optimization technique is demonstrated through its application to phantom and brain images. The authors show that the optimal pulse sequence parameters for a sequence of four MSE and one IR images almost doubles the smallest normalized SNR of the brain eigenimages, as compared to the conventional brain protocol.

Correction of phase effects produced by eddy currents in solvent suppressed 1H-CSI.

Accurate phasing of MRS spectra is often difficult unless time varying phase effects produced by gradient-induced eddy currents that persist during data acquisition are eliminated. This effect is particularly problematic in 1H-CSI spectra where frequency shifts produced by static field inhomogeneity and phase shifts produced by eddy currents combine. In this paper we present a method that corrects both shifts and eliminates manual phasing of individual CSI spectra typically required to recover a pure absorption line shape. The method uses a time domain phase correction derived from the ambient water signal acquired under identical conditions (i.e., acquisition parameters, gradient sequence) as the solvent-suppressed CSI data. Results from CSI experiments on phantoms and in vivo solvent suppressed 1H-CSI spectra from normal human brain are presented demonstrating the capabilities of the technique.

Predominantly extraaxial astroblastoma: imaging and proton MR spectroscopy features.

The CT, angiographic, MR, and proton MR spectroscopy findings in a case of astroblastoma, a rare neoplasm of glial cell origin, are presented. Of particular interest is the predominantly extraaxial location of the tumor. CT and MR demonstrated a complex mass consisting of a solid nodule and a peripheral septated cystic component. The extraaxial nature of the mass was suggested on MR.

Analysis of the evolution of focal cerebral ischemia in the rat using the eigenimage filter.

The eigenimage filter was used to evaluate the results of a MRI study of cerebral ischemia in a rat model. This linear filter segments a desired feature in an image sequence from other features which may interfere with its observation. The animals were imaged temporally, after occlusion of the middle cerebral artery, to investigate the evolution of the ischemic process. The temporal evolution of ischemia was evaluated by analysis of the "eigenimages," calculated T2 and T1 map images, and images for the angles between signature vectors defined in the eigenimage technique. The eigenimages and angle map images demonstrated an improved visibility of the lesion at all time points, as compared to the original images and T2 and T1 map images. The eigenimages also demonstrated signal intensity changes within the area of ischemia. These changes are speculated to be related to variations in local cerebral blood flow resulting in varying degrees of tissue damage. The eigenimage intensities and the angles between signature vectors demonstrated time-related changes similar to the T2 and T1 values. Since the eigenimage filter and angle calculations are not dependent upon physical models (like T2 and T1), and the errors associated with these models, they may be preferable as methods for tissue characterization.

Comparison of velocity-encoded MR imaging and fluid dynamic modeling of steady and disturbed flow.

The contrast of flow-encoded magnetic resonance (MR) images obtained in vivo and the accuracy of velocity measurements are complicated by the presence of complex flow states. The effects of complex flow states on MR flow-encoded images were studied and quantitative flow information was obtained with an MR phase-subtraction technique. Regions of complex flow, including flow stagnation and separation and laminar flow, could be clearly identified on the phase images. The MR imaging velocity measurements were validated by comparison with numerical simulation results for three-dimensional velocity distributions. The velocity MR images and the profiles obtained from the simulation generally agreed well for flow rates of 660 and 1,680 mL/min. This agreement lends support to both the fluid dynamic model and the physical basis of the phase imaging technique and establishes the validity of flow-encoded phase imaging as an in vivo flow quantitation method, especially under low Reynolds number flow conditions.

Importance of absence of CSF pulsation artifacts in the MR detection of significant myelographic block at 1.5 T.

MR imaging was performed on 21 patients who had high-grade myelographic block due to various diseases in all spinal compartments (extradural, intradural/extramedullary, and intramedullary) and in all portions of the spinal canal (cervical, thoracic, and lumbosacral). Loss of CSF pulsation artifacts due to significant compression of the spinal cord was demonstrated on non-motion-compensated T2-weighted examinations in each case. We believe that the absence of such artifacts on these sequences indicates significant spinal cord compression in patients without classic signs and symptoms of cord compression but with intraspinal disease identified on T1-weighted studies.

Eigenimage filtering in MR imaging: an application in the abnormal chest wall.

A postprocessing linear filter was applied to spin-echo images on 10 patients with known or suspected chest wall invasion due to bronchogenic carcinoma. This technique known as eigenimage filtering allows selective feature extraction of suspected abnormalities from conventional MR images. The final result is an image with marked increased contrast range through enhancement of a desired process (tumor) with suppression of an interfering process (e.g., normal surrounding tissue). This preliminary work demonstrates the ease with which the technique may be implemented, the contrast enhancement obtained between the desired and the interfering feature in the final eigenimage, and its ability to correct for partial volume averaging effects. Also demonstrated are artifacts that can interfere with the interpretation of the eigenimage and a method for minimizing these artifacts in the final eigenimage.

Meniscal abnormalities of the knee: 3DFT fast-scan GRASS MR imaging.

The ability to use fast-scan techniques to obtain MR images without sacrificing diagnostic accuracy is a desirable goal in MR imaging. We describe a series of patients in whom fast-scan MR imaging was found to be equal to conventional spin-echo imaging in the detection and characterization of meniscal abnormalities. Thirty-five patients with suspected meniscal tears were studied with fast-scan imaging (3DFT-GRASS), and the results were compared with those of conventional spin-echo imaging. Three-millimeter contiguous sections through the entire knee were obtained in 5 min by using the 3DFT-GRASS technique. 3DFT-GRASS and spin-echo images agreed in all cases regarding the presence or absence of an abnormality and its degree of severity. We conclude that fast-scan 3DFT-GRASS MR imaging is useful when screening the knee for the presence of meniscal abnormalities.

SAR reduced pulse sequences.

Three techniques were considered for reducing the RF (radiofrequency) power deposition in the body while maintaining scan time efficiency: reducing the RF peak amplitude while increasing the pulse width, substituting gradient echoes for spin echoes, and reducing the flip angle of the phase reversal pulse. The use of gradient echoes was found to be the most efficient means to reduce the power delivered to the patient and to obtain rapid data acquisition. The effect upon SAR (specific absorption rate) and SNR (signal-to-noise ratio) was demonstrated on a phantom when the phase reversal pulse was reduced from the standard 180 degrees to 90 degrees. Data in the body indicated a fairly constant SNR down to a refocusing flip angle between 110 degrees and 135 degrees. An initial clinical evaluation was performed at three institutions using the method of reducing the flip angle of the phase reversal pulse. The scan with theta = 120 degrees was rated by readers in a blinded study as having acceptable diagnostic image quality while the 135 degrees scan had comparable image quality to a conventional 90 degrees - 180 degrees pulse sequence. The use of reduced phase reversal pulses was seen as an efficient protocol to obtain T1-weighted images at rapid data rates while reducing the power delivered to the body by about 40%.

The development of a pH-sensitive contrast agent for NMR 1H imaging.

Fe(III)meso-tetra(4-sulfonatophenyl)porphine (Fe-TPPS4) has been investigated as a potential pH-sensitive nuclear magnetic resonance (NMR) proton image contrast agent. Relaxation rates (1/T1 and 1/T2) of water protons were measured as a function of pH and concentration of Fe-TPPS4 in phosphate-buffered isotonic saline. Transverse relaxation rates (1/T2) did not change appreciably with pH above 6.0. Longitudinal relaxation rates (1/T1) increased significantly between pH 7.75 and 5.75. This effect was more pronounced with the increasing concentration of Fe-TPPS4 from 0.1 to 1.5 mM and is attributed to a pH-dependent equilibrium between the high-spin (S = 5/2) Fe-TPPS4 monomer at low pH and the antiferromagnetically coupled mu-oxodimer O-(FeTPPS4)2 at high pH. The efficacy of this pH-dependent contrast agent is demonstrated in vitro.

Chest-wall invasion by carcinoma of the lung: detection by MR imaging.

Nineteen patients with bronchogenic carcinoma were studied by MR imaging to determine the presence of chest-wall invasion. All studies were carried out at 1.5 T, and the results were correlated with chest radiographs or CT scans. All MR studies were interpreted before surgery (13 cases) and without knowledge of the results of other radiologic studies. MR findings indicative of chest-wall invasion included a high-signal focus within the chest wall and/or chest-wall thickening with increased signal on spin-echo (SE) images having a repetition time of 2500 msec and an echo time of 50-100 msec (SE 2500/50-100). In one case, noncontour-deforming high-signal intensity within chest-wall musculature (but no other abnormality) was demonstrated on SE 2500/50-100 images. Coronal or sagittal imaging facilitated identification of tumor contiguity with extrathoracic structures in apical lesions. Contrast differences between normal and invaded chest wall on T2-weighted images were the most helpful in assessing chest-wall involvement. These preliminary observations indicate that MR imaging is useful in the evaluation of chest-wall invasion by carcinoma of the lung.

Automated analysis of multiple performance characteristics in magnetic resonance imaging systems.

As with other digital imaging systems in heavy medical use, it is desirable with magnetic resonance imaging (MRI) to obtain extensive, rigorous system performance measures from a small set of images of one or two relatively simple test objects. Digital analysis of the parallel square rod (PSR) test object introduces digital image system self-evaluation to MRI and extends automated image evaluation to include rigorous measures throughout the imaging volume rather than just average measures over the image. Precise comparisons with theory and between systems can be performed as well as quality control and corrections for nonuniformities. The PSR test object consists of an 18 X 18 X 36 cm rectangular acrylic container enclosing 60 parallel square acrylic rods running the entire length. The inter-rod space is filled with a liquid or gel that produces strong, tissuelike signals in MRI and high contrast relative to the rods for computed tomography (CT). For profiles of slice thickness and separation, the rods are tilted in the test object to intersect the image plane at a 45 degree angle when the test object sides are parallel and perpendicular to the image plane. The test object itself is rotated 6-12 degrees about its major axis so that the sides of the rods make a small angle to the rows and columns of pixels. This allows digital sampling at finer spacing than the pixels for determination of edge response functions.(ABSTRACT TRUNCATED AT 250 WORDS)