Günther Grabner

Diffusion-weighted MR for Differentiation of Breast Lesions at 3.0 T: How Does Selection of Diffusion Protocols Affect Diagnosis?

PURPOSEnTo compare the diagnostic quality of diffusion-weighted (DW) imaging schemes with regard to apparent diffusion coefficient (ADC) accuracy, ADC precision, and DW imaging contrast-to-noise ratio (CNR) for different types of lesions and breast tissue.nnnMATERIALS AND METHODSnInstitutional review board approval and written, informed consent were obtained. Fifty-one patients with histopathologic correlation or follow-up performed with a 3.0-T MR imager were included in this study. There were 112 regions of interest drawn in 24 malignant, 17 benign, 20 cystic, and 51 normal tissue regions. ADC maps were calculated for combinations of 10 b values (range, 0-1250 sec/mm(2)). Differences in ADC among tissue types were evaluated. The CNRs of lesions at DW imaging were compared for all b values. A repeated-measures analysis of variance was used to assess lesion differentiation.nnnRESULTSnADCs calculated from b values of 50 and 850 sec/mm(2) were 0.99 x 10(-3) mm(2)/sec +/- 0.18 (standard deviation), 1.47 x 10(-3) mm(2)/sec +/- 0.21, 1.85 x 10(-3) mm(2)/sec +/- 0.22, and 2.64 x 10(-3) mm(2)/sec +/- 0.30 for malignant, benign, normal, and cystic tissues, respectively. An ADC threshold level of 1.25 x 10(-3) mm(2)/sec allowed discrimination between malignant and benign lesions with a diagnostic accuracy of 95% (P < .001). ADC calculations performed with multiple b values were not significantly more precise than those performed with only two. We found an overestimation of ADC for maximum b values of up to 1000 sec/mm(2). The best CNR for tumors was identified at 850 sec/mm(2).nnnCONCLUSIONnOptimum ADC determination and DW imaging quality at 3.0 T was found with a combined b value protocol of 50 and 850 sec/mm(2). This provided a high accuracy for differentiation of benign and malignant breast tumors.

A combined high temporal and high spatial resolution 3 Tesla MR imaging protocol for the assessment of breast lesions: initial results.

Purpose:To develop a 3.0 Tesla breast imaging protocol that combines high temporal and spatial resolution three-dimensional MR sequences for quantitative time course and morphologic analysis of breast lesions. Materials and Methods:Thirty-four patients were included in the study (age range, 31–82; mean age, 54.3). The study protocol was approved by the Institutional Review Board and written informed consent was obtained from all patients. The magnetic resonance imaging protocol included: a coronal T1-weighted volume-interpolated-breathhold-examination sequence, focused on high temporal resolution for optimal assessment of the contrast-enhancement behavior of lesions (SI 1.7 mm isotropic; TA 3.45 minutes for 17 measurements); a coronal T1-weighted turbo fast-low-angle-shot-three-dimensional sequence, with water-excitation and fat suppression, focused on high spatial resolution for morphologic analysis (SI 1 mm isotropic; TA 2 minutes); and a repeated coronal volume-interpolated-breathhold-examination sequence for detection of washout. Lesion size and morphology were assessed. Region-of-interests for suspicious areas were manually drawn and evaluated for contrast-enhancement behavior by plotting intensity courses against time. Sensitivity and specificity with a 95% confidence interval and the negative predictive value and positive predictive value were calculated. Diagnostic accuracy was assessed. The histopathological diagnoses were used as a standard of reference. Results:Fifty-five lesions were detected in 34 patients. All malignant breast lesions were identified correctly. There were 5 false-positive lesions. The sensitivity of contrast-enhanced magnetic resonance imaging of the breast at 3 T was 100%, with a 95% confidence interval (CI) of 90.6% to 100%. The specificity was 72.2%, with a 95% CI of 49.1% to 87.5%. The positive predictive value was 0.88 and the negative predictive value was 1. Diagnostic accuracy was 91% with a 95% CI of 80.4% to 96.1%. Conclusion:Our prospective study demonstrates that the presented 3 Tesla MR imaging protocol, comprising both high temporal and high spatial resolution, enables accurate detection and assessment of breast lesions.

The topograpy of demyelination and neurodegeneration in the multiple sclerosis brain

Multiple sclerosis is characterized by widespread primary demyelination and progressive degeneration, driven by heterogeneous mechanisms. Haider et al. provide a topographic map of the frequency with which different brain regions are affected by these processes, and show that demyelination and neurodegeneration involve inflammatory as well as vascular changes.

Combining phase images from multi-channel RF coils using 3D phase offset maps derived from a dual-echo scan†

A method is presented for the combination of phase images from multi‐channel RF coils in the absence of a volume reference coil. It is based on the subtraction of 3D phase offset maps from the phase data from each coil. Phase offset maps are weighted combinations of phase measurements at two echo times. Multi‐Channel Phase Combination using measured 3D phase offsets (MCPC‐3D) offers a conceptually and computationally simple solution to the calculation of combined phase images. The dual‐echo data required for the phase maps can be intrinsic to the high‐resorlution gradient‐echo scan to be reconstructed (MCPC‐3D‐I). Alternatively, a separate, fast, low‐resolution dual‐echo scan can be used (MCPC‐3D‐II). Both variants are shown to give near perfect phase matching, yielding images with high SNR throughout and high GM‐WM contrast. MCPC‐3D is compared with other reference‐free phase image crombination methods; high‐pass phase filtering, phase difference imaging, and matching using constant offsets (MCPC‐C). Multi‐Channel Phase Combination using measured 3D phase offsets method does not need an overlap between the signals from individual coils and can be used with parallel imaging, making it ideally suited to multi‐channel coils with a large number of elements, and to high and ultra‐high field systems. Magn Reson Med, 2011.

Analysis of multiple sclerosis lesions using a fusion of 3.0 T FLAIR and 7.0 T SWI phase: FLAIR SWI

To improve multiple sclerosis (MS) research by introducing a new type of contrast, namely, the combination of fluid‐attenuated inversion recovery (FLAIR) data acquired at 3.0 T and 7.0 T susceptibility‐weighted imaging (SWI) phase data. The approach of this new contrast is whole‐brain coverage with 3.0 T‐FLAIR data for lesion detection—currently limited at 7.0 T due to specific absorption rate (SAR) limits—overlaid with high‐resolution, small vessel, and iron‐related 7.0 T SWI contrast. Lesion analysis in terms of penetrating veins and local iron depositions were performed.

Three-dimensional susceptibility-weighted imaging at 7 T using fractal-based quantitative analysis to grade gliomas

IntroductionSusceptibility-weighted imaging (SWI) with high- and ultra-high-field magnetic resonance is a very helpful tool for evaluating brain gliomas and intratumoral structures, including microvasculature. Here, we test whether objective quantification of intratumoral SWI patterns by applying fractal analysis can offer reliable indexes capable of differentiating glial tumor grades.MethodsThirty-six patients affected by brain gliomas (grades II–IV, according to the WHO classification system) underwent MRI at 7xa0T using a SWI protocol. All images were collected and analyzed by applying a computer-aided fractal image analysis, which applies the fractal dimension as a measure of geometrical complexity of intratumoral SWI patterns. The results were subsequently statistically correlated to the histopathological tumor grade.ResultsThe mean value of the fractal dimension of the intratumoral SWI patterns was 2.086u2009±u20090.413. We found a trend of higher fractal dimension values in groups of higher histologic grade. The values ranged from a mean value of 1.682u2009±u20090.278 for grade II gliomas to 2.247u2009±u20090.358 for grade IV gliomas (pu2009=u20090.013); there was an overall statistically significant difference between histopathological groups.ConclusionThe present study confirms that SWI at 7xa0T is a useful method for detecting intratumoral vascular architecture of brain gliomas and that SWI pattern quantification by means of fractal dimension offers a potential objective morphometric image biomarker of tumor grade.

Longitudinal brain imaging of five malignant glioma patients treated with bevacizumab using susceptibility-weighted magnetic resonance imaging at 7 T

Malignant glioma is a rare tumor type characterized by prominent vascular proliferation. Antiangiogenic therapy with the monoclonal antibody bevacizumab is considered as a promising therapeutic strategy, although the effect on tumor vascularization is unclear. High-field susceptibility-weighted imaging (SWI) visualizes the microvasculature and may contribute to the investigation of antiangiogenic therapy responses in gliomas. We prospectively studied five adult malignant glioma patients treated with bevacizumab-containing regimens. In each patient, we performed three 7-T SWI and T1-weighted imaging investigations (baseline and 2 and 4 weeks after the start of bevacizumab treatment). In addition, we imaged a postmortem brain of a patient with glioblastoma using 7-T SWI and performed detailed histopathological analysis. We observed almost total resolution of brain edema in three of five patients after initiation of bevacizumab therapy. In one case with rapid increase of the lesion size despite bevacizumab therapy, SWI showed progressive increase of irregular hypointense structures, most likely corresponding to increasing amounts of pathological microvasculature. In one case with progressive neurological decline, 7-T images showed multiple intratumoral microhemorrhages after the first bevacizumab application. Correlation of postmortem neuroimaging with histopathology confirmed that SWI-positive structures correspond to tumor vasculature. The experience from our case series indicates that longitudinal 7-T SWI seems to be an appropriate method for investigation of changes in brain tumor vascularization over time under antiangiogenic therapy.

High-field, high-resolution, susceptibility-weighted magnetic resonance imaging: improved image quality by addition of contrast agent and higher field strength in patients with brain tumors

IntroductionTo demonstrate intratumoral susceptibility effects in malignant brain tumors and to assess visualization of susceptibility effects before and after administration of the paramagnetic contrast agent MultiHance (gadobenate dimeglumine; Bracco Imaging), an agent known to have high relaxivity, with respect to susceptibility effects, image quality, and reduction of scan time.MethodsIncluded in the study were 19 patients with malignant brain tumors who underwent high-resolution, susceptibility-weighted (SW) MR imaging at 3xa0T before and after administration of contrast agent. In all patients, Multihance was administered intravenously as a bolus (0.1xa0mmol/kg body weight). MR images were individually evaluated by two radiologists with previous experience in the evaluation of pre- and postcontrast 3-T SW MR images with respect to susceptibility effects, image quality, and reduction of scan time.ResultsIn the 19 patients 21 tumors were diagnosed, of which 18 demonstrated intralesional susceptibility effects both in pre- and postcontrast SW images, and 19 demonstrated contrast enhancement in both SW images and T1-weighted spin-echo MR images. Conspicuity of susceptibility effects and image quality were improved in postcontrast images compared with precontrast images and the scan time was also reduced due to decreased TE values from 9xa0min (precontrast) to 7xa0min (postcontrast).ConclusionThe intravenous administration of MultiHance, an agent with high relaxivity, allowed a reduction of scan time from 9xa0min to 7xa0min while preserving excellent susceptibility effects and image quality in SW images obtained at 3xa0T. Contrast enhancement and intralesional susceptibility effects can be assessed in one sequence.

Slow expansion of multiple sclerosis iron rim lesions: pathology and 7 T magnetic resonance imaging

In multiple sclerosis (MS), iron accumulates inside activated microglia/macrophages at edges of some chronic demyelinated lesions, forming rims. In susceptibility-based magnetic resonance imaging at 7xa0T, iron-laden microglia/macrophages induce a rim of decreased signal at lesion edges and have been associated with slowly expanding lesions. We aimed to determine (1) what lesion types and stages are associated with iron accumulation at their edges, (2) what cells at the lesion edges accumulate iron and what is their activation status, (3) how reliably can iron accumulation at the lesion edge be detected by 7xa0T magnetic resonance imaging (MRI), and (4) if lesions with rims enlarge over time in vivo, when compared to lesions without rims. Double-hemispheric brain sections of 28 MS cases were stained for iron, myelin, and microglia/macrophages. Prior to histology, 4 of these 28 cases were imaged at 7xa0T using post-mortem susceptibility-weighted imaging. In vivo, seven MS patients underwent annual neurological examinations and 7xa0T MRI for 3.5xa0years, using a fluid attenuated inversion recovery/susceptibility-weighted imaging fusion sequence. Pathologically, we found iron rims around slowly expanding and some inactive lesions but hardly around remyelinated shadow plaques. Iron in rims was mainly present in microglia/macrophages with a pro-inflammatory activation status, but only very rarely in astrocytes. Histological validation of post-mortem susceptibility-weighted imaging revealed a quantitative threshold of iron-laden microglia when a rim was visible. Slowly expanding lesions significantly exceeded this threshold, when compared with inactive lesions (pxa0=xa00.003). We show for the first time that rim lesions significantly expanded in vivo after 3.5xa0years, compared to lesions without rims (pxa0=xa00.003). Thus, slow expansion of MS lesions with rims, which reflects chronic lesion activity, may, in the future, become an MRI marker for disease activity in MS.

Fractal Analysis of the Susceptibility Weighted Imaging Patterns in Malignant Brain Tumors During Antiangiogenic Treatment: Technical Report on Four Cases Serially Imaged by 7 T Magnetic Resonance During a Period of Four Weeks

OBJECTIVEnThe need for new and objective indexes for the neuroradiologic follow-up of brain tumors and for monitoring the effects of antiangiogenic strategies in vivo led us to perform a technical study on four patients who received computerized analysis of tumor-associated vasculature with ultra-high-field (7 T) magnetic resonance imaging (MRI). The image analysis involved the application of susceptibility weighted imaging (SWI) to evaluate vascular structures.nnnMETHODSnFour patients affected by recurrent malignant brain tumors were enrolled in the present study. After the first 7-T SWI MRI procedure, the patients underwent antiangiogenic treatment with bevacizumab. The imaging was repeated every 2 weeks for a period of 4 weeks. The SWI patterns visualized in the three MRI temporal sequences were analyzed by means of a computer-aided fractal-based method to objectively quantify their geometric complexity.nnnRESULTSnIn two clinically deteriorating patients we found an increase of the geometric complexity of the space-filling properties of the SWI patterns over time despite the antiangiogenic treatment. In one patient, who showed improvement with the therapy, the fractal dimension of the intratumoral structure decreased, whereas in the fourth patient, no differences were found.nnnCONCLUSIONSnThe qualitative changes of the intratumoral SWI patterns during a period of 4 weeks were quantified with the fractal dimension. Because SWI patterns are also related to the presence of vascular structures, the quantification of their space-filling properties with fractal dimension seemed to be a valid tool for the in vivo neuroradiologic follow-up of brain tumors.