Effect of contrast material injection protocol on first-pass myocardial perfusion assessed by dual-energy dual-layer computed tomography

Background: Dual-energy dual-layer computed tomography (CT) scanners can provide useful tools, such as iodine maps and virtual monochromatic images (VMI), for the evaluation of myocardial perfusion defects. Data about the influence of acquisition protocols and normal values are still lacking. Methods: Clinically indicated coronary CT-angiographies performed between January-October 2018 in a single university hospital with dual-energy dual-layer CT (DE-DLCT) and different injection protocols were retrospectively evaluated. The two protocols were: 35 mL in patients <80 kg and 0.5 mL/kg in patients >80 kg at 2.5 mL/sec (group A) or double contrast dose at 5 mL/sec (group B). Patients with coronary stenosis >50% were excluded. Regions of interest were manually drawn on 16 myocardial segments and iodine concentration was measured in mg/mL. Signal-to-noise, contrast-to-noise ratios (CNR) and image noise were measured on conventional images and VMI. Results: A total of 30 patients were included for each protocol. With iodine concentrations of 1.38 +/- 0.41 mg/mL for protocol A and 2.07 +/- 0.73 mg/mL for protocol B, the two groups were significantly different (P<0.001). No significant iodine concentration differences were found between the 16 segments (P=0.47 and P=0.09 for group A and B respectively), between basal, mid and apical segments for group A and B (P=0.28 and P=0.12 for group A and B respectively) and between wall regions for group A (P=0.06 on normalised data). In group B, iodine concentration was significantly different between three wall regions [highest values for the lateral wall, median =2.03 (1.06) mg/mL]. Post-hoc analysis showed highest contrast-to-noise and signal-to-noise in VMI at 40 eV (P<0.05). Conclusions: Iodine concentration in left ventricular myocardium of patients without significant coronary artery stenosis varied depending on the injection protocol and appeared more heterogeneous in different wall regions at faster injection rate and greater iodine load. Signal-to-noise and contrast-to-noise gradually improved when decreasing VMI energy, although at the expenses of higher noise, demonstrating the potential of DE-DLCT to enhance objective image quality

Velocity-based cardiac self-gating in free-running radial 4D Flow MRI

International audienceIntroduction: Free-running whole-heart acquisitions with the capability of deriving cardiac self-gating (SG) signals present clear interest, particularly at 3T, where the ECG signal suffers from the magnetohydrodynamic effect and acquisition related noise. Our goal was to develop a novel velocity-based cardiac SG strategy for free-running radial 4D Flow imaging and to investigate the impact of cardiac SG on the velocity quantification in the thoracic aorta. Methods: We implemented a free-running interleaved (8 spokes/interleaf) 3D radial velocity mapping sequence on a 1.5T Philips Ingenia (Philips, Best, The Netherlands), based on a spiral phyllotaxis pattern [1]. Imaging was performed on the thorax of 5 healthy subjects as follows: TE/TR 2.5/6 ms, FA=6•, VENC=180-240 cm/s, 2.5 mm isotropic voxel, acquisition time: 8-12 minutes. First, a sliding-window reconstruction using 64 consecutive spokes and a step of 8 spokes yielded high temporal and low spatial resolution velocity resolved volumes. The average speed in the aorta was obtained for each volume, using a mask drawn on the fully sampled reconstruction. Then, to obtain the cardiac SG signal, the temporal evolution of the aorta average speed was filtered in the frequency domain and interpolated using multiscale kernel ridge regression [2]. Finally, the cardiac SG signal and the ECG were used to bin the data in the same number of cardiac phases (N=12-18). Cardiac and velocity resolved images were then reconstructed offline using a compressed sensing algorithm implemented in Matlab (The Mathworks, Inc, Natick, MA). Velocity measurements in the thoracic aorta were then compared between SG and ECG based gating. Results: A comparison of the frequency analysis of the temporal evolution of the aorta speed and the ECG signal is presented in Figure A for a representative case. The frequency peak corresponding to the heart rate and the first harmonic can be observed at the same location. Despite similar average RR intervals between SG and ECG, the R-peak detection precision for SG was 50ms on average. Velocity quantification showed underestimation of peak systolic values for SG compared to ECG (Figure B). In order to confirm that the underestimation is due to the R-peak detection precision, we simulated 1% and 5% variability in the R-peak location in the ECG signal by random sampling according to a uniform distribution and used this simulated signal for cardiac binning. Similar to SG, an underestimation can be observed for the same case in the average speed (Figure C). Discussion: We present here a novel approach to cardiac SG specifically dedicated to 4D Flow MRI. Our results are in agreement with previously reported results using a navigator spoke based method for cardiac SG in 3D radial [3]. While this precision does not affect the resulting anatomical images, we have shown an impact on the velocity quantification, particularly an underestimation of the peak systolic values. This underestimation was described previously for 3D radial 4D Flow [1], however its source was not completely identified. Improvement of the precision in the R-peak detection is expected with the use of more advanced methods in the sliding window reconstruction. In addition, a respiratory SG signal can be obtained in absolute values and enable respiratory motion correction (not shown). This is an advantage of our method, compared to other previous fully self-gated strategies

In vitro, nonrigid model of aortic arch aneurysm

[DOI:\hrefhttps://dx.doi.org/10.1016/j.jvir.2008.02.00910.1016/j.jvir.2008.02.009] [PubMed:\hrefhttps://www.ncbi.nlm.nih.gov/pubmed/1850390818503908]International audienceTo develop and validate a controlled patient-derived process for producing an in vitro, nonrigid model of aortic arch aneurysm.\ A three-dimensional magnetic resonance (MR) angiogram derived from a patient with an aortic arch aneurysm was segmented by using a homemade software package, meshed and converted to Standard Tessellation Language (STL) file format. The authors transferred this format to a stereolithography machine to produce a replica of the entire aorta, including the arch aneurysm and supraaortic arteries, by pouring silicone rubber.\ A sturdy, life-size, soft, transparent plastic cast, accurately reproducing both the internal and external anatomy of the aortic aneurysm, was produced in less than 1 week. Comparison between the STL file format of MR angiographic images of both the patient's aorta and model enabled validation of the reliability of the manufacturing process.\ The combination of easy segmentation and conversion to the STL file format with stereolithography techniques enabled a realistic, life-size, silicone vascular phantom to be created from a live patient imaging dataset

Human Knee Phantom for Spectral CT: Validation of a Material Decomposition Algorithm

International audienceOsteoarthritis is the most common degenerative joint disease. Spectral computed tomography generates energy-resolved data which enable identification of materials within the sample and offer improved soft tissue contrast compared to conventional X-ray CT. In this work, we propose a realistic numerical phantom of a knee to assess the feasibility of spectral CT for osteoarthritis. The phantom is created from experimental synchrotron CT mono-energetic images. After simulating spectral CT data, we perform material decomposition using Gauss-Newton method, for different noise levels. Then, we reconstruct virtual mono-energetic images. We compare decompositions and mono-energetic images with the phantom using mean-squared error. When performing material decomposition and tomographic reconstruction, we obtain less than 1 % error for both, using noisy data. Moreover , it is possible to see cartilage with naked eye on virtual mono-energetic images. This phantom has great potential to assess the feasibility and current limitations of spectral CT to characterize knee osteoarthritis

High-resolution magnetic resonance imaging at 2 Tesla: potential for atherosclerotic lesions exploration in the apolipoprotein E knockout mouse

International audienceINTRODUCTION: The aim of the present study was to evaluate the potential of high-resolution MRI at 2 Tesla (T) for direct noninvasive imaging of the aortic wall in a mouse model of atherosclerosis.MATERIAL AND METHODS: A specific mouse antenna was developed and sequence parameters were adjusted. T(1)- and T2-weighted images of abdominal aorta were obtained at 2 T with a spatial resolution of 86 x 86 x 800 microm3 in vivo. With a dedicated small coil, ex vivo MRI of the aorta was performed with a spatial resolution of 54 x 54 x 520 microm3.RESULTS: In vivo, the aortic wall was clearly defined on T(2)-weighted images in 15 of 16 mice: along the aorta the lumen circumference ranged from 1.07 to 3.61 mm and mean wall thickness from 0.11 to 0.67 mm. In vivo measurements of plaque distribution were confirmed by ex vivo MR imaging and by histology, with a good correlation with histology regarding lumen circumference (r = 0.94) and wall thickness (r = 0.97).CONCLUSION: Magnetic resonance imaging at 2 T to analyze in vivo atherosclerotic lesions in mice is possible with a spatial resolution of 86 x 86 x 800 microm3 and thus can be used for noninvasive follow-up in evaluation of new drugs

In vivo magnetic resonance imaging of large spontaneous aortic aneurysms in old apolipoprotein E-deficient mice

[PubMed:\hrefhttps://www.ncbi.nlm.nih.gov/pubmed/1537793715377937]International audienceOld ApoE-deficient mice were studied in vivo by magnetic resonance imaging (MRI) to prospectively evaluate vascular remodeling associated with atherosclerotic lesions.\ Old female ApoE-/- mice on a normal diet were followed by MRI at 2 Tesla for a 3-month period and killed for histopathology. Aortic dimensions were measured and compared.\ High-quality in vivo MR images were obtained at 2 Tesla with in plane spatial resolution of 86 X 86 microm2. On MRI, aortic lumen enlargement (>1.5-fold dilation) was seen in 10 of 13 mice, located predominantly in the suprarenal portion of the aorta. The mean maximal diameter of the aneurysms and of the aorta above and below the aneurysm were, respectively, 1.12 +/- 0.32 mm and 0.53 +/- 0.08 mm by MRI and 1.3+/- 0.41 mm and 0.55 +/- 0.15 mm by histology. Matched histologic cross-sections of the aortic wall showed medial degradation with rupture of the internal elastic lamina at multiple sites, associated with fibrolipidic plaque containing cholesterol crystals.\ Aortic lumen enlargement was diagnosed in old ApoE-/- mice at sites with advanced atherosclerotic plaques. MRI has potential both as an in vivo imaging technique for screening mouse models for vascular wall pathology and to follow arterial remodeling associated with the disease progression