Analytic image concept combined to SENSE reconstruction

Object: Two approaches of reconstructing undersampled partial k-space data, acquired with multiple coils are compared: homodyne detection combined with SENSE (HM_SENSE) and analytic image reconstruction combined with SENSE (AI_SENSE). The latter overcomes limitations of HM_ SENSE by considering aliased images as analytic thus avoiding the need for phase correction required for HM_SENSE. Materials and methods: In vivo imaging experiments were carried out in male Lewis rats using both gradient echo and spin echo sequences. Accelerated images obtained by using the various reconstruction algorithms were compared to fully sampled reference images both qualitatively and quantitatively. Results: For the various sampling patterns evaluated, both HM_SENSE and AI_SENSE were found to yield robust image reconstruction with small deviations from the reference image. Even for high acceleration factors AI_SENSE still provided useful results and was found superior compared to HM_SENSE. Conclusion: Combination of partial k-space sampling and parallel image acquisition allows for further acceleration of data acquisition as compared to each method alone. Image reconstruction from undersampled data sets using the AI_SENSE algorithm was found to considerably reduce reconstruction errors and artifacts observed for HM_SENSE reconstruction caused by errors in phase estimatio

Accelerated cardiovascular magnetic resonance of the mouse heart using self-gated parallel imaging strategies does not compromise accuracy of structural and functional measures

BACKGROUND: Self-gated dynamic cardiovascular magnetic resonance (CMR) enables non-invasive visualization of the heart and accurate assessment of cardiac function in mouse models of human disease. However, self-gated CMR requires the acquisition of large datasets to ensure accurate and artifact-free reconstruction of cardiac cines and is therefore hampered by long acquisition times putting high demands on the physiological stability of the animal. For this reason, we evaluated the feasibility of accelerating the data collection using the parallel imaging technique SENSE with respect to both anatomical definition and cardiac function quantification. RESULTS: Findings obtained from accelerated data sets were compared to fully sampled reference data. Our results revealed only minor differences in image quality of short- and long-axis cardiac cines: small anatomical structures (papillary muscles and the aortic valve) and left-ventricular (LV) remodeling after myocardial infarction (MI) were accurately detected even for 3-fold accelerated data acquisition using a four-element phased array coil. Quantitative analysis of LV cardiac function (end-diastolic volume (EDV), end-systolic volume (ESV), stroke volume (SV), ejection fraction (EF) and LV mass) in healthy and infarcted animals revealed no substantial deviations from reference (fully sampled) data for all investigated acceleration factors with deviations ranging from 2% to 6% in healthy animals and from 2% to 8% in infarcted mice for the highest acceleration factor of 3.0. CNR calculations performed between LV myocardial wall and LV cavity revealed a maximum CNR decrease of 50% for the 3-fold accelerated data acquisition when compared to the fully-sampled acquisition. CONCLUSIONS: We have demonstrated the feasibility of accelerated self-gated retrospective CMR in mice using the parallel imaging technique SENSE. The proposed method led to considerably reduced acquisition times, while preserving high spatial resolution at sufficiently high CNR. The accuracy of measurements of both structural and functional parameters of the mouse heart was not compromised by the application of the proposed accelerated data acquisition method

Increasing temporal resolution of DSC perfusion MRI using the analytic image concept

Object: Dynamic susceptibility contrast MRI (DSC-MRI) is increasingly being used to evaluate cerebral microcirculation. In this study, the use of the analytic image reconstruction (AIR), with the aim to increase the temporal resolution, is evaluated for DSC-MRI in small animals. Materials and methods: Imaging was performed using a T 2*- weighted sequence to acquire male Lewis rats raw data. Results show that AIR satisfactory reconstructs DSC-MRI while preserving a good reconstruction quality and the image characteristics compared to the full k-space and keyhole reconstructed images. The combination of the choice of the baseline image and the proposed asymmetric acquisition schema enables an increase in temporal resolution, by a factor of four, thus having more sample points for better estimating perfusion parameters. Results: Computer simulations result in a mean cerebral blood volume of 1.22 that deviates from the full k-space value by −3% and a mean cerebral blood flow of 1.97 deviating from the full k-space value by −3% when the mean transit time did not change. Even if these deviations increase when achieving real acquisitions, AIR still better computes quantitative values than keyhole. Conclusion: AIR allows a good reconstruction of the dynamic stage of the image series thus leading to better dynamic effects analysi

Accurate assessment of carotid artery stenosis in atherosclerotic mice using accelerated high-resolution 3D magnetic resonance angiography

Object: High-resolution magnetic resonance angiography (MRA) enables non-invasive detection and longitudinal monitoring of atherosclerosis in mouse models of human disease. However, MRA is hampered by long acquisition times putting high demands on the physiological stability of the animal. Therefore, we evaluated the feasibility of accelerated MRA using the parallel imaging technique SENSE with regard to both lesion detection and quantification. Materials and methods: MRA acquisitions of supra-aortic vessels were performed in ApoE −/− mice that have been shown to develop atherosclerotic plaques. Findings obtained from accelerated data sets were compared to fully sampled reference data sets and histology. Results: Our results revealed only minor differences in detecting vascular lesions for data collections accelerated by factors of up to 3.3 using a four-element coil array. For vessels with a mean lumen diameter of 500μm, morphometry of stenotic lesions revealed no substantial deviations from reference (fully sampled) data for all investigated acceleration factors. For the highest acceleration factor of 3.3, an average deviation of the degree of stenosis of 4.9 ± 3.6% was found. Common carotid stenoses assessed by in vivo MRA displayed a good correlation with histological analyses (slope of linear regression = 0.97, R 2 = 0.98). Conclusion: According to the results of this work, we have demonstrated the feasibility and accuracy of accelerated high-resolution 3D ToF MRA in mice suitable for detailed depiction of mouse supra-aortic vessels and amenable to non-invasive quantification of small atherosclerotic lesion

Accelerated dynamic Fourier velocity encoding by exploiting velocity-spatio-temporal correlations

Objective: To describe how the information content in a Fourier velocity encoding (FVE) scan can be transformed into a very sparse representation and to develop a method that exploits the compactness of the data to significantly accelerate the acquisition. Materials and Methods: For validation, fully sampled FVE datasets were acquired in phantom and in vivo experiments. Fivefold and eightfold acceleration was simulated by using only one fifth or one eighth of the data for reconstruction in the proposed method based on the k-t BLAST framework. Reconstructed images were compared quantitatively to those from the fully sampled data. Results: Velocity spectra in the accelerated datasets were comparable to the spectra from fully sampled datasets. The detected peak velocities remained accurate even at eightfold acceleration, and the overall shape of the spectra was well preserved. Slight temporal smoothing was seen in the accelerated datasets. Conclusion: A novel technique for accelerating time-resolved FVE scan is presented. It is possible to accelerate FVE to acquisition speeds comparable to a standard time-resolved phase-contrast sca

Increasing temporal resolution of DSC perfusion MRI using the analytic image concept

ISSN:0968-5243ISSN:1352-866

Oral administration of 17beta-estradiol over 3 months without progestin co-administration does not improve coronary flow reserve in post-menopausal women: a randomized placebo-controlled cross-over CMR study

BACKGROUND: Several large epidemiological outcome studies did not demonstrate a benefit of combined estrogen-progestin replacement treatment (HRT) on cardiovascular events in elderly postmenopausal women. Whether progestin antagonism is responsible for these negative results or the natural estrogen 17ss-estradial (E2) itself is not effective in the coronary circulation is unknown. AIM: To assess the effect of 3 months of E2 treatment on the coronary circulation, i.e., on coronary flow reserve (CFR), in postmenopausal women without established coronary artery disease (CAD). METHODS: In a double-blind placebo-controlled cross-over design postmenopausal women (60 +/- 5 years, n = 14) were randomized to either start with placebo or E2 (Estrofem, Novo Nordisk, Copenhagen, Denmark) 2 mg/d given orally over 3 months and to switch thereafter for another 3 months of therapy. At baseline, a stress echocardiography was performed to exclude CAD. CFR was determined by coronary sinus CMR flow measurements (with motion-adapted gating and interactive acquisition window control; spatial/temporal resolution of 0.8 x 0.9 mm2/25-30 ms) which were performed at rest and during vasodilation (dipyridamole 0.56 mg/kg over 4 minutes IV) at baseline, and after 3 and 6 months of therapy, respectively. RESULTS: Hemodynamics such as heart rate and systolic and diastolic blood pressure were not different for the control and E2 group. For CFR and for resting and hyperemic coronary sinus blood flow, no differences between the placebo and E2 group were found (2-way ANOVA for repeated measurements). Reproducibility of phase-contrast CMR measurements of CFR was -1.1 +/- 4.9%. CONCLUSIONS: In elderly postmenopausal women without significant CAD, oral administration of E2 over 3 months without a progestin co-administration does not improve CFR. This finding yields partly explanation for some large epidemiological trials which could not demonstrate a clinical cardiovascular benefit of HRT in elderly women

MRI signature in a novel mouse model of genetically induced adult oligodendrocyte cell death

Two general pathological processes contribute to multiple sclerosis (MS: acute inflammation and degeneration. While magnetic resonance imaging (MRI) is highly sensitive in detecting abnormalities related to acute inflammation both clinically and in animal models of experimental autoimmune encephalomyelitis (EAE), the correlation of these readouts with acute and future disabilities has been found rather weak. This illustrates the need for imaging techniques addressing neurodegenerative processes associated with MS.In the present work we evaluated the sensitivity of different MRI techniques (T2 mapping, macrophage tracking based on labeling cells in vivo by ultrasmall particles of iron oxide (USPIO), diffusion tensor imaging (DTI) and magnetization transfer imaging (MTI)) to detect histopathological changes in a novel animal model making use of intrinsic, temporally and spatially controlled triggering of oligodendrocyte cell death. This mouse model allows studying the MRI signature associated to neurodegenerative processes of MS in the absence of adaptive inflammatory components that appear to be foremost in the EAE models. Our results revealed pronounced T2 hyperintensities in brain stem and cerebellar structures, which we attribute to structural alteration of white matter by pronounced vacuolation. Brain areas were found devoid of significant macrophage infiltration in line with the absence of a peripheral inflammatory response. The significant decrease in diffusion anisotropy derived from DTI measures in these structures is mainly caused by a pronounced decrease in diffusivity parallel to the fiber indicative of axonal damage.Triggering of oligodendrocyte ablation did not translate into a significant increase in radial diffusivity. Only minor decreases in MT ratio have been observed, which is attributed to inefficient removal of myelin debris