Flow Artifacts Research Articles

Subretinal Hyperreflective Material Imaged With Optical Coherence Tomography Angiography

The range of subretinal hyperreflective material (SHRM) seen in macular disease includes type 2 macular neovascularization, fibrosis, exudation, vitelliform material, and hemorrhage. The prognostic significance of SHRM has been evaluated retrospectively in clinical trials, but discriminating SHRM subtypes traditionally requires multiple imaging modalities. The purpose of this study is to describe optical coherence tomography angiography (OCTA) flow characteristics and artifacts that might help to distinguish SHRM subtypes. Validity analysis. Patients with age-related macular degeneration (AMD), myopia, pachychoroid disease, and macular dystrophy, manifesting SHRM on optical coherence tomography (OCT), were recruited. Clinical chart review and multimodal imaging established the SHRM subtype. All patients underwent OCTA. OCT and OCTA images were examined together for (1) intrinsic flow, (2) retinal projection onto the anterior SHRM surface (strong, weak, absent), (3) retinal projection through SHRM onto retinal pigment epithelium (RPE), and (4) masking of choriocapillaris flow. Thirty-three eyes of 25 patients were included (type 2 neovascularization×3; fibrosis×4; exudation×10; hemorrhage×5; vitelliform×17). Mean age per eye was 76 years (standard deviation: 12). Intrinsic flow was strongest in type 2 neovascularization. Subretinal fibrosis showed limited flow in residual large-caliber vessels and branches. Flow was not detected within foci of exudation, hemorrhage, or vitelliform lesions. Retina-SHRM surface projection was strongest onto smooth-surfaced SHRM and weaker onto exudation. Retinal projection was weakest on the surface of vitelliform lesions. Retina-RPE projection was masked by dense hemorrhage and vitelliform material. In compound SHRM, OCTA distinguished between vascular and avascular components. Optical coherence tomography angiography can distinguish vascular from avascular SHRM components. OCTA artifacts may distinguish certain avascular SHRM components.

Three-Dimensional CAIPIRINHA SPACE TSE for 5-Minute High-Resolution MRI of the Knee.

The aim of this study was to prospectively test the hypothesis that a 2-dimensional (2D) CAIPIRINHA (controlled aliasing in parallel imaging results in higher acceleration) sampling pattern facilitates 5-minute high spatial resolution 3-dimensional (3D) sampling perfection with application optimized contrast using different flip angle evolutions (SPACE) magnetic resonance imaging (MRI) of the knee with image quality similar or better than current 2D turbo spin echo (TSE) and 3D SPACE standards. The study was approved by our institutional review board. Twenty asymptomatic subjects (12 men, 8 women; mean age, 42 years; age range, 24-65 years) underwent 3 T MRI of the knee. A 4-fold accelerated 3D SPACE TSE prototype with 2D CAIPIRINHA sampling pattern and 5-minute acquisition time was compared with commercially available 2-fold and 4-fold accelerated 3D SPACE and 2D TSE pulse sequences with acquisition times of 11 minutes and 15 seconds, 6 minutes and 30 seconds, as well as 9 minutes and 48 seconds, respectively. Outcome variables included image quality, anatomic visibility, signal-to-noise ratio (SNR), and contrast-to-noise ratio (CNR). Statistical analysis included Friedman, repeated measures analysis of variances, and Cohen's weighted κ tests. Bonferroni-corrected P values of 0.005 and less were considered statistically significant. Overall, image quality, visibility of anatomic structures, SNR, and CNR of 3D CAIPIRINHA SPACE were statistically similar to 2-fold accelerated 3D SPACE and significantly better than 4-fold accelerated 3D SPACE, which exhibited degrading parallel imaging artifacts. Compared with 2.5-mm 2D TSE images, 0.5-mm 3D CAIPIRINHA SPACE images showed statistically similar good edge sharpness and very good contrast resolution, and significantly less partial volume as well as absent chemical shift and pulsatile flow artifacts. Visibility of menisci, anterior cruciate ligament, posterior cruciate ligament, medial collateral ligament, and lateral collateral ligament was good to very good on 0.5-mm 3D CAIPIRINHA SPACE images as compared with good on 2.5-mm 2D TSE image (P < 0.005). The SNR of fat, fluid, and cartilage as well as CNR between cartilage, fluid, fat, posterior cruciate ligament, and menisci were minimally higher on 2.5-mm 2D TSE image (P < 0.005). Image quality, visibility of anatomic structures, SNR, and CNR of 2.5-mm 3D CAIPIRINHA SPACE and 2.5-mm 2D TSE images were good to very good without significant differences. Three-dimensional SPACE with 2D CAIPIRINHA sampling pattern enables high-quality 3D TSE MRI of the knee at an acquisition time of 5 minutes and image quality, visibility of anatomic structures, SNR, and CNR similar to conventional 3D SPACE and 2D TSE, both of which require approximately 10-minute acquisition times.

Introduction.

To demonstrate possible flow artifacts when imaging drusen with optical coherence tomography angiography (OCTA). Patients with drusen were enrolled in a prospective OCT study using the Zeiss AngioPlex OCTA instrument (Carl Zeiss Meditec, Dublin, CA). Two kinds of en face slabs were created for visualizing both structure and flow. The first slab followed the contour of Bruch's membrane. The second slab had an inner boundary following the retinal pigment epithelium (RPE) contour and an outer boundary following the contour of Bruch's membrane. The structure and flow signals from within the drusen were compared. Eleven eyes of nine patients with age-related macular degeneration and drusen were imaged. In all 11 eyes, an artifactual flow signal was seen on the first slab where it intersected the RPE. This flow signal was a projection artifact from the overlying retinal vessels. The second slab did not show evidence of flow within drusen. OCTA decorrelation projection artifacts can be misinterpreted as apparent flow within drusen if the slab region includes hyperreflective boundary layers such as the RPE. [Ophthalmic Surg Lasers Imaging Retina. 2016;47:517-522.].

Fast 3D ultrashort echo-time spiral projection imaging using golden-angle: A flexible protocol for in vivo mouse imaging at high magnetic field.

To develop a fast three-dimensional (3D) k-space encoding method based on spiral projection imaging (SPI) with an interleaved golden-angle approach and to validate this novel sequence on small animal models. A disk-like trajectory, in which each disk contained spirals, was developed. The 3D encoding was performed by tilting the disks with a golden angle. The sharpness was first calculated at different T2* values. Then, the sharpness was measured on phantom using variable undersampling ratios. Finally, the sampling method was validated by whole brain time-of-flight angiography and ultrasmall superparamagnetic iron oxide (USPIO) enhanced free-breathing liver angiography on mouse. The in vitro results demonstrated the robustness of the method for short T2* and high undersampling ratios. In vivo experiments showed the ability to properly detect small vessels in the brain with an acquisition time shorter than 1 min. Free-breathing mice liver angiography showed the insensitivity of this protocol toward motions and flow artifacts, and enabled the visualization of liver motion during breathing. The method implemented here allowed fast 3D k-space sampling with a high undersampling ratio. Combining the advantages of center-out spirals with the flexibility of the golden angle approach could have major implications for real-time imaging. Magn Reson Med 77:1831-1840, 2017. © 2016 International Society for Magnetic Resonance in Medicine.

Kinetic depth images: flexible generation of depth perception

In this paper we present a systematic approach to create smoothly varying images from a pair of photographs to facilitate enhanced awareness of the depth structure of a given scene. Since our system does not rely on sophisticated display technologies such as stereoscopy or auto-stereoscopy for depth awareness, it (a) is inexpensive and widely accessible, (b) does not suffer from vergence - accommodation fatigue, and (c) works entirely with monocular depth cues. Our approach enhances the depth awareness by optimizing across a number of features such as depth perception, optical flow, saliency, centrality, and disocclusion artifacts. We report the results of user studies that examine the relationship between depth perception, relative velocity, spatial perspective effects, and the positioning of the pivot point and use them when generating kinetic-depth images. We also present a novel depth re-mapping method guided by perceptual relationships based on the results of our user study. We validate our system by presenting a user study that compares the output quality of our proposed method against other existing alternatives on a wide range of images.

Flow artifact removal in carotid wall imaging based on black and gray-blood dual-contrast images subtraction

To develop and validate a dual-contrast image subtraction (DCIS) strategy for eliminating the flow artifacts in black-blood carotid MRI. Twelve patients with carotid stenosis and eight healthy volunteers were imaged using the black and gray-blood dual-contrast imaging based on the relaxation-enhanced compressed sensing three-dimensional motion-sensitizing driven equilibrium prepared rapid-gradient-echo (RECS-3D MERGE) sequence. Subtraction of black-blood images (BBIs) and gray-blood images (GBIs), together with a preweighting procedure, was performed to eliminate the residual blood signal in BBIs. A wavelet denoising procedure was applied to offset the noise amplification. In addition to the lumen signal-to-noise ratio (SNR) and wall-lumen contrast-to-noise ratio (CNR), the signal variance ratio (SVR) and contrast variance ratio (CVR) were also used to evaluate the blood suppression efficiency. By choosing the weighting factor of one, the lumen SNR of DCIS images was approximately 1% of that of the original BBIs, and the CNR showed a 91.4% improvement as compared with the BBIs. The median of the lumen SVR decreased to zero, and the CVR increased to 123% of that of the BBIs. DCIS is demonstrated to be an effective strategy for sufficiently removing the residual flow signal from black-blood carotid MRI. Magn Reson Med 77:1612-1618, 2017. © 2016 International Society for Magnetic Resonance in Medicine.

Time Efficient 3D Radial UTE Sampling with Fully Automatic Delay Compensation on a Clinical 3T MR Scanner

This work’s aim was to minimize the acquisition time of a radial 3D ultra-short echo-time (UTE) sequence and to provide fully automated, gradient delay compensated, and therefore artifact free, reconstruction. The radial 3D UTE sequence (echo time 60 μs) was implemented as single echo acquisition with center-out readouts and improved time efficient spoiling on a clinical 3T scanner without hardware modifications. To assess the sequence parameter dependent gradient delays each acquisition contained a quick calibration scan and utilized the phase of the readouts to detect the actual k-space center. This calibration scan does not require any user interaction. To evaluate the robustness of this automatic delay estimation phantom experiments were performed and 19 in vivo imaging data of the head, tibial cortical bone, feet and lung were acquired from 6 volunteers. As clinical application of this fast 3D UTE acquisition single breath-hold lung imaging is demonstrated. The proposed sequence allowed very short repetition times (TR~1ms), thus reducing total acquisition time. The proposed, fully automated k-phase based gradient delay calibration resulted in accurate delay estimations (difference to manually determined optimal delay −0.13 ± 0.45 μs) and allowed unsupervised reconstruction of high quality images for both phantom and in vivo data. The employed fast spoiling scheme efficiently suppressed artifacts caused by incorrectly refocused echoes. The sequence proved to be quite insensitive to motion, flow and susceptibility artifacts and provides oversampling protection against aliasing foldovers in all directions. Due to the short TR, acquisition times are attractive for a wide range of clinical applications. For short T2* mapping this sequence provides free choice of the second TE, usually within less scan time as a comparable dual echo UTE sequence.

Estimation of Skin Blood Flow Artefacts in NIRS Signals During a Verbal Fluency Task.

The aim of this study was to clarify effects of skin (scalp) blood flow on functional near infrared spectroscopy (fNIRS) during a verbal fluency task. In the present study, to estimate the influence of skin blood flow on fNIRS signals, we conducted examinations on 19 healthy volunteers (39.9±13.1 years, 11 male and 8 female subjects). We simultaneously measured the fNIRS signals, skin blood flow (i.e., flow, velocity, and number of red blood cells [RBC]), and pulse wave rates using a multimodal fNIRS system. We found that the effects of skin blood flow, measured by the degree of interference of the flow, velocity, and number of RBCs, and pulse wave rates, on NIRS signals varied considerably across subjects. Further, by using the above physiological parameters, we evaluated application of the independent component analysis algorithm proposed by Molgedey and Schuster (MS-ICA) to remove skin blood flow artefacts from fNIRS signals.

A Spiral Spin-Echo MR Imaging Technique for Improved Flow Artifact Suppression in T1-Weighted Postcontrast Brain Imaging: A Comparison with Cartesian Turbo Spin-Echo.

A challenge with the T1-weighted postcontrast Cartesian spin-echo and turbo spin-echo brain MR imaging is the presence of flow artifacts. Our aim was to develop a rapid 2D spiral spin-echo sequence for T1-weighted MR imaging with minimal flow artifacts and to compare it with a conventional Cartesian 2D turbo spin-echo sequence. T1-weighted brain imaging was performed in 24 pediatric patients. After the administration of intravenous gadolinium contrast agent, a reference Cartesian TSE sequence with a scanning time of 2 minutes 30 seconds was performed, followed by the proposed spiral spin-echo sequence with a scanning time of 1 minutes 18 seconds, with similar spatial resolution and volumetric coverage. The results were reviewed independently and blindly by 3 neuroradiologists. Scores from a 3-point scale were assigned in 3 categories: flow artifact reduction, subjective preference, and lesion conspicuity, if any. The Wilcoxon signed rank test was performed to evaluate the reviewer scores. The t test was used to evaluate the SNR. The Fleiss κ coefficient was calculated to examine interreader agreement. In 23 cases, spiral spin-echo was scored over Cartesian TSE in flow artifact reduction (P < .001). In 21 cases, spiral spin-echo was rated superior in subjective preference (P < .001). Ten patients were identified with lesions, and no statistically significant difference in lesion conspicuity was observed between the 2 sequences. There was no statistically significant difference in SNR between the 2 techniques. The Fleiss κ coefficient was 0.79 (95% confidence interval, 0.65-0.93). The proposed spiral spin-echo pulse sequence provides postcontrast images with minimal flow artifacts at a faster scanning time than its Cartesian TSE counterpart.

Isotropic 3D black blood MRI of abdominal aortic aneurysm wall and intraluminal thrombus

IntroductionThe aortic wall and intraluminal thrombus (ILT) have been increasingly studied as potential markers of progressive disease with abdominal aortic aneurysms (AAAs). Our goal was to develop a high resolution, 3D black blood MR technique for AAA wall and ILT imaging within a clinically acceptable scan time. MethodsTwenty two patients with AAAs (maximal diameter 4.3±1.0cm), along with five healthy volunteers, were imaged at 3T with a 3D T1-weighted fast-spin-echo sequence using variable flip angle trains (SPACE) with a preparation pulse (DANTE) for suppressing blood signal. Volunteers and ten patients were also scanned with SPACE alone for comparison purposes. The signal to noise ratio (SNR) and the aortic wall/ILT to lumen contrast to noise ratio (CNR) were measured. Qualitative image scores (1–4 scale) assessing the inner lumen and outer wall boundaries of AAA were performed by two blinded reviewers. In patients with ILT, the ratio of ILT signal intensity (ILTSI) over psoas muscle SI (MuscleSI) was calculated, and the signal heterogeneity of ILT was quantified as standard deviation (SD) over the mean. ResultsAll subjects were imaged successfully with an average scan time of 7.8±0.7minutes. The DANTE preparation pulse for blood suppression substantially reduced flow artifacts in SPACE with lower lumen SNR (8.8 vs. 21.4, p<0.001) and improved the wall/ILT to lumen CNR (9.9 vs. 6.3, p<0.001) in patients. Qualitative assessment showed improved visualization of lumen boundaries (73% higher scores on average, p=0.01) and comparable visualization of outer wall boundary (p>0.05). ILT was present in ten patients, with relatively high signal and a wide SD (average ILTSI/MuscleSI 1.42±0.48 (range 0.75–2.11)) and with SD/mean of 27.7%±6.6% (range 19.6%–39.4%). ConclusionHigh resolution, 3D black blood MRI of AAAs can be achieved in a clinical accepted scan time with reduction of flow artifacts using the DANTE preparation pulse. Signal characteristics of ILT can be quantified and may be used for improved patient-specific risk stratification.

Elimination of motion and pulsation artifacts using BLADE sequences in shoulder MR imaging.

To evaluate the ability of proton-density with fat-suppression BLADE (proprietary name for periodically rotated overlapping parallel lines with enhanced reconstruction in MR systems from Siemens Healthcare, PDFS BLADE) and turbo inversion recovery magnitude-BLADE (TIRM BLADE) sequences to reduce motion and pulsation artifacts in shoulder magnetic resonance examinations. Forty-one consecutive patients who had been routinely scanned for shoulder examination participated in the study. The following pairs of sequences with and without BLADE were compared: (a) Oblique coronal proton-density sequence with fat saturation of 25 patients and (b) oblique sagittal T2 TIRM-weighed sequence of 20 patients. Qualitative analysis was performed by two experienced radiologists. Image motion and pulsation artifacts were also evaluated. In oblique coronal PDFS BLADE sequences, motion artifacts have been significantly eliminated, even in five cases of non-diagnostic value with conventional imaging. Similarly, in oblique sagittal T2 TIRM BLADE sequences, image quality has been improved, even in six cases of non-diagnostic value with conventional imaging. Furthermore, flow artifacts have been improved in more than 80% of all the cases. The use of BLADE sequences is recommended in shoulder imaging, especially in uncooperative patients because it effectively eliminates motion and pulsation artifacts.

SU-E-I-67: Arachnoid Cysts: The Role of the BLADE Technique

Purpose: The purpose of this study is first to show the extent by which BLADE sequences can reduce all the image artifacts and second to verify that the usefulness of this technique in certain pathological conditions is significant. Methods: In this study, fourteen consecutive patients (5 females, 9 males), who routinely underwent MRI brain examination, between 2010–2014, were selected. The applied routine protocols for brain MR examination included the following sequences: 1) T2-W FLAIR axial; 2) T2-W TSE axial; 3) T2*-W axial, 4) T1-W TSE sagittal; 5) DWI-W axial; 6) T1-W TSE axial; 7) T1-W TSE axial+contrast. In cases of cystic tumors, the T2-W FLAIR BLADE sequence was added to the protocol. All the images were evaluated independently at two separate settings with 3 weeks interval by two radiologists. The radiologists also evaluated the presence of image artifacts (motion, flow, chemical shift, Gibbs ringing). To evaluate the size of the cyst, the two radiologists compared the two techniques (conventional and BLADE) by assessing the extent of the divergence in the measurements of the cysts. Results: Regarding the extent of the cyst size, BLADE measurements were found to be more reliable than the conventional ones with the differences being statistically significantmore » (p<0.01). The qualitative measurements indicated that the T2 FLAIR BLADE sequences were superior to the conventional T2 FLAIR with statistically significant differences (p<0.001) in the following characteristics: 1) overall image quality, 2) CSF nulling; 3) contrast at the pathology and its surrounding; 4) limits of the pathology; 5) motion artifacts; 6) flow artifacts; 7) chemical shift artifacts and 8) Gibbs ringing artifacts. Conclusion: BLADE sequence was found to decrease both flow artifacts in the temporal lobes and motion artifacts from the orbits and it is proposed for clinical use.« less

Photothermal optical lock-in optical coherence tomography for in vivo imaging.

Photothermal OCT (PTOCT) provides high sensitivity to molecular targets in tissue, and occupies a spatial imaging regime that is attractive for small animal imaging. However, current implementations of PTOCT require extensive temporal sampling, resulting in slow frame rates and a large data burden that limit its in vivo utility. To address these limitations, we have implemented optical lock-in techniques for photothermal optical lock-in OCT (poli-OCT), and demonstrated the in vivo imaging capabilities of this approach. The poli-OCT signal was assessed in tissue-mimicking phantoms containing indocyanine green (ICG), an FDA approved small molecule that has not been previously imaged in vivo with PTOCT. Then, the effects of in vivo blood flow and motion artifact were assessed and attenuated, and in vivo poli-OCT was demonstrated with both ICG and gold nanorods as contrast agents. Experiments revealed that poli-OCT signals agreed with optical lock-in theory and the bio-heat equation, and the system exhibited shot noise limited performance. In phantoms containing biologically relevant concentrations of ICG (1 µg/ml), the poli-OCT signal was significantly greater than control phantoms (p<0.05), demonstrating sensitivity to small molecules. Finally, in vivo poli-OCT of ICG identified the lymphatic vessels in a mouse ear, and also identified low concentrations (200 pM) of gold nanorods in subcutaneous injections at frame rates ten times faster than previously reported. This work illustrates that future in vivo molecular imaging studies could benefit from the improved acquisition and analysis times enabled by poli-OCT.

Flow void artifact mimicking aneurysm in the anterior communicating artery region on T1- and T2-weighted images.

We observed an unusual magnetic resonance imaging (MRI) artifact on T1- and T2-weighted sequences resembling an aneurysm in the region of anterior communicating artery (ACoA) in a child patient. A 6-year-old patient with neurofibromatosis underwent brain MRI for a follow-up investigation. Imaging was performed at 1.5 T scanner (Philips Gyroscan Intera, Best, Netherlands). The protocol consisted of axial and coronal T2-weighted turbo spin echo images [repetition time (TR) =4,616 ms, echo time (TE) =100 ms, slice thickness =5 mm, spacing between slices =1 mm, field of view (FOV) =260 mm × 182 mm, acquisition matrix: 228×150, echo train length =15], and 3D T1-weighted turbo field echo [TR =8.27 ms, TE =3.83 ms, flip angle =8°, FOV =256 mm × 192 mm, acquisition matrix: 116×93, Sensitivity Encoding (SENSE) acceleration factor (out-of-plane) =3]. Signal void near ACoA resembling an aneurysm was observed on axial and coronal T2-weighted and T1-weighted images ( Figure 1A-C ). The signal void was initially interpreted as an aneurysm based on its appearance on three sequences. Time-of-flight (TOF) angiography was requested and performed on a different scanner (1.5 T, Magnetom Aera, Siemens, Erlangen, Germany) together with conventional MRI. The second MRI showed no evidence of aneurysm ( Figure 1D-F ) indicating the findings in the first acquisition to be an artifact. What is interesting about this artifact is its appearance on three sequences (T2 axial, T2 coronal, and 3D T1) contrary to the acknowledged radiological rule that artifacts usually appear in one sequence. In practice, if a radiologist suspects an unseemly signal to be an artifact on an axial image, he/she checks with coronal/sagittal images and other sequences to confirm his interpretation. Since the signal void appeared on both turbo spin echo (T2-weighted) and turbo field echo (T1-weighted) sequences, it was independent of magnetic resonance (MR) sequence. We came to the conclusion that it is a flowvoid artifact in the region of ACoA where flow dynamics is complex (1). ACoA bridges two anterior cerebral arteries, separates the junction between A1 and A2 segments, and gives rise to a number of small branches. Due to its complex anatomy, flow direction changes at ACoA. This may cause disorderly and turbulent flow and formation of eddy currents. Turbulent flow causes dephasing of proton signal, resulting in signal loss artifacts on conventional MRI, mimicking aneurysms. False aneurysms in the ACoA due to flow effects were reported to occur on TOF MR angiograms (2,3). When evaluating such lesions on conventional MRI, the possibility of being a flow artifact should be kept in mind and the techniques such as TOF angiography should be exploited prior to invasive techniques such as catheter angiography (2).

4D spiral imaging of flows in stenotic phantoms and subjects with aortic stenosis.

The utility of four-dimensional (4D) spiral flow in imaging of stenotic flows in both phantoms and human subjects with aortic stenosis is investigated. The method performs 4D flow acquisitions through a stack of interleaved spiral k-space readouts. Relative to conventional 4D flow, which performs Cartesian readout, the method has reduced echo time. Thus, reduced flow artifacts are observed when imaging high-speed stenotic flows. Four-dimensional spiral flow also provides significant savings in scan times relative to conventional 4D flow. In vitro experiments were performed under both steady and pulsatile flows in a phantom model of severe stenosis (one inch diameter at the inlet, with 87% area reduction at the throat of the stenosis) while imaging a 6-cm axial extent of the phantom, which included the Gaussian-shaped stenotic narrowing. In all cases, gradient strength and slew rate for standard clinical acquisitions, and identical field of view and resolution were used. For low steady flow rates, quantitative and qualitative results showed a similar level of accuracy between 4D spiral flow (echo time [TE] = 2 ms, scan time = 40 s) and conventional 4D flow (TE = 3.6 ms, scan time = 1:01 min). However, in the case of high steady flow rates, 4D spiral flow (TE = 1.57 ms, scan time = 38 s) showed better visualization and accuracy as compared to conventional 4D flow (TE = 3.2 ms, scan time = 51 s). At low pulsatile flow rates, a good agreement was observed between 4D spiral flow (TE = 2 ms, scan time = 10:26 min) and conventional 4D flow (TE = 3.6 ms, scan time = 14:20 min). However, in the case of high flow-rate pulsatile flows, 4D spiral flow (TE = 1.57 ms, scan time = 10:26 min) demonstrated better visualization as compared to conventional 4D flow (TE = 3.2 ms, scan time = 14:20 min). The feasibility of 4D spiral flow was also investigated in five normal volunteers and four subjects with mild-to-moderate aortic stenosis. The approach achieved TE = 1.68 ms and scan time = 3:44 min. The conventional sequence achieved TE = 2.9 ms and scan time = 5:23 min. In subjects with aortic stenosis, we also compared both MRI methods with Doppler ultrasound (US) in the measurement of peak velocity, time to peak systolic velocity, and eject time. Bland-Altman analysis revealed that, when comparing peak velocities, the discrepancy between Doppler US and 4D spiral flow was significantly less than the discrepancy between Doppler and 4D Cartesian flow (2.75 cm/s vs. 10.25 cm/s), whereas the two MR methods were comparable (-5.75 s vs. -6 s) for time to peak. However, for the estimation of eject time, relative to Doppler US, the discrepancy for 4D conventional flow was smaller than that of 4D spiral flow (-16.25 s vs. -20 s). Relative to conventional 4D flow, 4D spiral flow achieves substantial reductions in both the TE and scan times; therefore, utility for it should be sought in a variety of in vivo and complex flow imaging applications.

Distributed capillary adiabatic tissue homogeneity model in parametric multi-channel blind AIF estimation using DCE-MRI.

One of the main challenges in quantitative dynamic contrast-enhanced (DCE) MRI is estimation of the arterial input function (AIF). Usually, the signal from a single artery (ignoring contrast dispersion, partial volume effects and flow artifacts) or a population average of such signals (also ignoring variability between patients) is used. Multi-channel blind deconvolution is an alternative approach avoiding most of these problems. The AIF is estimated directly from the measured tracer concentration curves in several tissues. This contribution extends the published methods of multi-channel blind deconvolution by applying a more realistic model of the impulse residue function, the distributed capillary adiabatic tissue homogeneity model (DCATH). In addition, an alternative AIF model is used and several AIF-scaling methods are tested. The proposed method is evaluated on synthetic data with respect to the number of tissue regions and to the signal-to-noise ratio. Evaluation on clinical data (renal cell carcinoma patients before and after the beginning of the treatment) gave consistent results. An initial evaluation on clinical data indicates more reliable and less noise sensitive perfusion parameter estimates. Blind multi-channel deconvolution using the DCATH model might be a method of choice for AIF estimation in a clinical setup.

Ruptured traumatic ovarian artery pseudoaneurysm in a pregnant patient.

A woman at 36 weeks' gestation was involved in a motor vehicle crash. She required emergency delivery of a healthy infant by cesarean section. She received anticoagulation, despite a splenic injury, for a possible inferior vena cava clot. She re-presented with new retroperitoneal hemorrhage around the juxtarenal aorta. A computed tomography scan suggested a vague contrast blush anterior to the aorta. Arteriography disclosed a right ovarian artery pseudoaneurysm, which was treated with microcoil embolization. The patient has subsequently recovered fully. In major trauma in pregnant patients, ovarian artery pathology needs to be considered in the differential diagnosis of post-traumatic hemorrhage.

Effect of segmentation of k-space in SSFP flow artifacts

Background Steady State Free Precession is a fast technique with high contrast between myocardium and blood in cardiovascular MR imaging. According to the time consuming data acquisition and short cardiac cycle (almost 0.9 second), data is obtained in several heartbeats depending on the number of frames and K-space size. The K-Space is divided to segments and each segment is acquired in one cardiac cycle. However, spins in the flowing blood do not experience enough pulses to reach the steady state condition. As a result, shadows called flow artifacts appear in images. In this study, we investigate the flow artifacts and in particular, how the number of frames (or segments) and in-plane velocity affect them.

Estimation of the flow motion in SSFP images using moving shadows; reliable or not?

Background SSFP plays an important role in cardiovascular MRI due to its high speed and unrivaled contrast between blood and myocardium. Some “flow artifacts”, however, rises because blood flow prevents spins from reaching the steady state. One artifact in this category is the moving shadows in the blood pool that appear to represent the actual flow behavior. In this study, we show that the shadows are not necessarily representing actual flow behavior. Therefore, cardiologists should consider the moving shadows cautiously to avoid misinterpretations.

Positive contrast high-resolution 3D-cine imaging of the cardiovascular system in small animals using a UTE sequence and iron nanoparticles at 4.7, 7 and 9.4T.

BackgroundTo show that 3D sequences with ultra-short echo times (UTEs) can generate a positive contrast whatever the magnetic field (4.7, 7 or 9.4 T) and whatever Ultra Small Particles of Iron Oxide (USPIO) concentration injected and to use it for 3D time-resolved imaging of the murine cardiovascular system with high spatial and temporal resolutions.MethodsThree different concentrations (50, 200 and 500 μmol Fe/kg) of USPIO were injected in mice and static images of the middle part of the animals were acquired at 4.7, 7 and 9.4 T pre and post-contrast with UTE (TE/TR = 0.05/4.5 ms) sequences. Signal-to-Noise Ratio (SNR) and Contrast-to-Noise Ratio (CNR) of blood and static tissus were evaluated before and after contrast agent injection. 3D-cine images (TE/TR = 0.05/3.5 ms, scan time < 12 min) at 156 μm isotropic resolution of the mouse cardiopulmonary system were acquired prospectively with the UTE sequence for the three magnetic fields and with an USPIO dose of 200 μmol Fe/kg. SNR, CNR and signal homogeneity of blood were measured. High spatial (104 μm) or temporal (3.5 ms) resolution 3D-cine imaging (scan time < 35 min) isotropic resolution were also performed at 7 T with a new sequence encoding scheme.ResultsUTE imaging generated positive contrast and higher SNR and CNR whatever the magnetic field and the USPIO concentration used compared to pre-contrast images. Time-resolved 3D acquisition enables high blood SNR (66.6 ± 4.5 at 7 T) and CNR (33.2 ± 4.2 at 7 T) without flow or motion artefact. Coronary arteries and aortic valve were visible on images acquired at 104 μm resolution.ConclusionsWe have demonstrated that by combining the injection of iron nanoparticles with 3D-cine UTE sequences, it was possible to generate a strong positive contrast between blood and surrounding tissues. These properties were exploited to produce images of the cardiovascular system in small animals at high magnetic fields with a high spatial and temporal resolution. This approach might be useful to measure the functional cardiac parameters or to assess anatomical modifications to the blood vessels in cardio-vascular disease models.Electronic supplementary materialThe online version of this article (doi:10.1186/s12968-015-0167-4) contains supplementary material, which is available to authorized users.