T. Stadnik

A method for myelin fiber orientation mapping using diffusion-weighted MR images

In the past, the anisotropic diffusion of water molecules in white matter in the brain has been correlated to the basic symmetry of the myelin fibers: water diffuses more readily along the fiber direction than perpendicular to it. As a consequence, diffusion sensitized magnetic resonance imaging can be expected to be useful for studying the fiber orientation. In this work, we present a method for exploiting this type of information to map the fiber orientations in the image plane. It makes use of three diffusion-weighted images with sensitizing gradients along x, y and u, an axis at 45 degrees with respect to x and y. The orientation information contained in these images is summarized in a single image representing the angle between the fiber direction and a fixed axis, making use of a cyclic color scale. The method is evaluated using computer simulations for a variety of diffusion weighting strengths and signal-to-noise ratios, tested on a phantom and illustrated on an in vivo example. An extension to the determination of the fiber orientation in three dimensions is also described.

Breast imaging. Preoperative breast cancer staging: comparison of USPIO-enhanced MR imaging and 18F-fluorodeoxyglucose (FDC) positron emission tomography (PET) imaging for axillary lymph node staging--initial findings.

Magnetic resonance (MR) imaging after ultra-small super paramagnetic iron oxide (USPIO) injection and 18F-fluorodeoxyglucose positron emission tomography (FDG-PET) for preoperative axillary lymph node staging in patients with breast cancer were evaluated using histopathologic findings as the reference standard. USPIO-enhanced MR and FDG-PET were performed in ten patients with breast cancer who were scheduled for surgery and axillary node resection. T2-weighted fast spin echo, T1-weighted three-dimensional (3D) gradient echo, T2*-weighted gradient echo and gadolinium-enhanced T1-weighted 3D gradient echo with spectral fat saturation were evaluated. MR imaging before USPIO infusion was not performed. The results were correlated with FDG-PET (acquired with dedicated PET camera, visual analysis) and histological findings. The histopathologic axillary staging was negative for nodal malignancy in five patients and positive in the remaining five patients. There was one false positive finding for USPIO-enhanced MR and one false negative finding for FDG-PET. A sensitivity (true positive rate) of 100%, specificity (true negative rate) of 80%, positive predictive value of 80%, and negative predictive value of 100% were achieved for USPIO-enhanced MR and of 80%, 100%, 100%, 80% for FDG-PET, respectively. The most useful sequences in the detection of invaded lymph nodes were in the decreasing order: gadolinium-enhanced T1-weighted 3D gradient echo with fat saturation, T2*-weighted 2D gradient echo, T1-weighted 3D gradient echo and T2-weighted 2D spin echo. In our study, USPIO-enhanced T1 gradient echo after gadolinium injection and fat saturation emerged as a very useful sequence in the staging of lymph nodes. The combination of USPIO-enhanced MR and FDG-PET achieved 100% sensitivity, specificity, PPV and NPV. If these results are confirmed, the combination of USPIO MR with FDG-PET has the potential to identify the patient candidates for axillary dissection versus sentinel node lymphadenectomy.

Quantification of renal perfusion and function on a voxel‐by‐voxel basis: A feasibility study

The feasibility of a voxel‐by‐voxel deconvolution analysis of T1‐weighted DCE data in the human kidney and its potential for obtaining quantification of perfusion and filtration was investigated. Measurements were performed on 14 normal humans and 1 transplant at 1.5 T using a Turboflash sequence. Signal time‐courses were converted to tracer concentrations and deconvolved with an aorta AIF. Parametric maps of relative renal blood flow (rRBF), relative renal volume of distribution (rRVD), relative mean transit time (rMTT), and whole cortex extraction fraction (E) were obtained from the impulse response functions. For the normals average cortical rRBF, rRVD, rMTT, and E were 1.6 mL/min/mL (SD 0.8), 0.4 mL/mL (SD 0.1), 17s (SD 7), and 22.6% (SD 6.1), respectively. A gradual voxelwise rRBF increase is found from the center of two infarction zones toward the edges. Voxel IRFs showed more detail on the nefron substructure than ROI IRFs. In conclusion, quantitative voxelwise perfusion mapping based on deconvolved T1‐DCE renal data is feasible, but absolute quantification requires inflow correction. rRBF maps and quantitative values are sufficiently sensitive to detect perfusion abnormality in pathologic areas, but further research is necessary to separate perfusion from extraction and to characterize the different compartments of the nephron on the (sub)voxel level. Magn Reson Med, 2005.

Prognostic value of perfusion-weighted imaging in brain glioma: a prospective study

SummaryObject. Biopsy targeting based on MR imaging alone may fail to identify malignant areas in brain gliomas. Considering the differences in relative Cerebral Blood Volume (rCBV) ratios reported among tumour grades, we evaluated whether perfusion-weighted MR imaging (PWI) could usefully implement the routine preoperative imaging by detecting those areas bearing a higher yield for malignancy to guide the stereotactic biopsy or the surgical removal.Clinical material and methods. We studied a series of 55 consecutive patients with newly diagnosed brain glioma using both conventional MR imaging and PWI in the preoperative assessment. The pathological diagnosis was established by stereotactic biopsy in 29 cases and by craniotomy in 24 cases. We evaluated the patient survival to detect undergrading.Discussion. Independent from contrast-enhancement, perfusion-weighted MR imaging improved the target selection in stereotactic biopsy guidance and the removal of malignant areas in tumours amenable to surgery. Particularly sensitive to the perfused part of the tumour as to small regional changes, rCBV maps allowed a better detection of malignant areas. The rCBV ratios correlated significantly to the tumour grade and the final outcome (p < 0.01).Conclusions. We found PWI valuable in the preoperative assessment of brain gliomas, discriminating high from low-grade gliomas. PWI can easily be performed on widely available MR imaging systems as part of the routine imaging of gliomas.

Deconvolution-based Dynamic Contrast-enhanced MR Imaging of Breast Tumors: Correlation of Tumor Blood Flow with Human Epidermal Growth Factor Receptor 2 Status and Clinicopathologic Findings—Preliminary Results

PURPOSE To prospectively determine whether breast carcinomas possess characteristic values of tumor blood flow (TBF) that correlate with pathologic and molecular prognostic markers. MATERIALS AND METHODS The institutional ethics committee approved this study. After informed consent was obtained, 57 women (age range, 31-80 years) with histologically proved breast cancer underwent routine magnetic resonance (MR) mammography, which included a whole-breast dynamic contrast material-enhanced (DCE) sequence. A second contrast material bolus was injected during dynamic single-section turbo field-echo imaging of the section where the lesion was maximally enhanced. The relative signal intensity changes were deconvolved in a pixelwise fashion to yield the TBF. Formalin-fixed paraffin-embedded tumor specimens on slides were evaluated for histologic size and grade, as well as for estrogen receptor (ER), progesterone receptor (PR), and human epidermal growth factor receptor 2 (HER2) protein. In patients with a HER2 protein score of 2+ or 3+, HER2 gene status was assessed. For all prognostic parameters, the Mann-Whitney U test was used to compare median TBF in the HER2-positive group with that in the HER2-negative group. RESULTS Significantly higher TBF was observed in tumors larger than 2 cm in diameter and in PR-negative and HER2 gene-amplified tumors (P < .05). In the HER2-positive and HER2-negative groups, ER-positive PR-positive tumors had a lower median TBF than did ER-negative PR-negative tumors, and the difference was significant in the HER2-positive group (P < .05). CONCLUSION Pixelwise deconvolution analysis of DCE MR data in patients with breast cancer can provide preoperative information regarding TBF. These results also support the hypothesis that there is increased TBF in HER2-positive tumors.

Choice of the regularization parameter for perfusion quantification with MRI.

Truncated singular value decomposition (TSVD) is an effective method for the deconvolution of dynamic contrast enhanced (DCE) MRI. Two robust methods for the selection of the truncation threshold on a pixel-by-pixel basis--generalized cross validation (GCV) and the L-curve criterion (LCC)--were optimized and compared to paradigms in the literature. GCV and LCC were found to perform optimally when applied with a smooth version of TSVD, known as standard form Tikhonov regularization (SFTR). The methods lead to improvements in the estimate of the residue function and of its maximum, and converge properly with SNR. The oscillations typically observed in the solution vanish entirely, and perfusion is more accurately estimated at small mean transit times. This results in improved image contrast and increased sensitivity to perfusion abnormalities, at the cost of 1-2 min in calculation time and hyperintense clusters in the image. Preliminary experience with clinical data suggests that the latter problem can be resolved using spatial continuity and/or hybrid thresholding methods. In the simulations GCV and LCC are equivalent in terms of performance, but GCV thresholding is faster.

Quantification of perfusion and permeability in breast tumors with a deconvolution-based analysis of second-bolus T1-DCE data.

To test the feasibility of using a second‐bolus injection, added to a routine breast MRI examination, to measure regional perfusion and permeability in human breast tumors.

Deconvolution of dynamic contrast-enhanced MRI data by linear inversion: Choice of the regularization parameter

Truncated singular value decomposition (TSVD) is an effective method for the deconvolution of dynamic contrast‐enhanced MRI. Two robust methods for the selection of the truncation threshold on a pixel‐by‐pixel basis—generalized cross validation (GCV) and the L‐curve criterion (LCC)—were optimized and compared to paradigms in the literature. The methods lead to improvements in the estimate of the residue function and of its maximum and converge properly with SNR. The oscillations typically observed in the solution vanish entirely and perfusion is more accurately estimated at small mean transit times. This results in improved image contrast and increased sensitivity to perfusion abnormalities, at the cost of 1–2 min in calculation time and isolated instabilities in the image. It is argued that the latter problem may be resolved by optimization. Simulated results for GCV and LCC are equivalent in terms of performance, but GCV is faster. Magn Reson Med 52:209–213, 2004.

Pituitary microadenomas: diagnosis with dynamic serial CT, conventional CT and T1-weighted MR imaging before and after injection of gadolinium.

PURPOSE The few studies comparing CT and MR in the diagnosis of pituitary microadenomas give discordant results. This prospective study compares the value of dynamic serial CT (DSCT), conventional CT (CCT), pre-Gd T1-weighted spin echo (T1SE-Gd) and post-Gd T1-weighted SE (T1SE+Gd) in the detection of pituitary microadenomas. METHODS The value of CT and MR was assessed in 17 cases, with the surgical confirmation as reference. The CTs and MRs were independently and blindly evaluated by two neuroradiologists. Because the finding at MR and/or CT influenced the selection of patients for surgery, the positive predictive value was calculated. The sensitivity calculation applies only for a specific group of postsurgical patients with positive CT and/or MR (marked with an asterisk for these reasons). RESULTS In this study, the highest sensitivity* (88% and 82%, respectively, for observers I and II) was achieved by DSCT. The T1SE-Gd and T1SE+Gd (evaluated separately) were slightly inferior (sensitivity* of 76% for observer I). The combination of T1SE-Gd with T1SE+Gd improved the sensitivity* to 94% and 82% respectively, for observers I and II. There was also moderate improvement of sensitivity* by combination of DSCT with conventional CT (94% for observer I). CONCLUSION These results suggest that rapid injection of a large amount of contrast conjointly with a fast scanning through the pituitary is crucial for the confident detection of microprolactinomas. Taking into account the similar results of the combination DSCT + CT and T1SE-Gd + T1SE+Gd in the detection of microprolactinomas, high field MRI is the first step modality in the evaluation of presumed hypophyseal hyperprolactinemia.

Diffusion-weighted MRI in cyclosporin A neurotoxicity for the classification of cerebral edema

Abstract. Cyclosporin A, an immunosuppressive agent, is known to have neurotoxic effects, but until now, there has not been agreement on the underlying mechanism. Our report suggests, by using diffusion-weighted MRI, that the brain lesions caused by cyclosporin A, are probably related to vasogenic edema. This may explain the complete recovery of the lesions on imaging when cyclosporine therapy is stopped.