Fast Spin-echo Pulse Sequence Research Articles

Modern acceleration in musculoskeletal MRI: applications, implications, and challenges.

Magnetic resonance imaging (MRI) is crucial for accurately diagnosing a wide spectrum of musculoskeletal conditions due to its superior soft tissue contrast resolution. However, the long acquisition times of traditional two-dimensional (2D) and three-dimensional (3D) fast and turbo spin-echo (TSE) pulse sequences can limit patient access and comfort. Recent technical advancements have introduced acceleration techniques that significantly reduce MRI times for musculoskeletal examinations. Key acceleration methods include parallel imaging (PI), simultaneous multi-slice acquisition (SMS), and compressed sensing (CS), enabling up to eightfold faster scans while maintaining image quality, resolution, and safety standards. These innovations now allow for 3- to 6-fold accelerated clinical musculoskeletal MRI exams, reducing scan times to 4 to 6min for joints and spine imaging. Evolving deep learning-based image reconstruction promises even faster scans without compromising quality. Current research indicates that combining acceleration techniques, deep learning image reconstruction, and superresolution algorithms will eventually facilitate tenfold accelerated musculoskeletal MRI in routine clinical practice. Such rapid MRI protocols can drastically reduce scan times by 80-90% compared to conventional methods. Implementing these rapid imaging protocols does impact workflow, indirect costs, and workload for MRI technologists and radiologists, which requires careful management. However, the shift from conventional to accelerated, deep learning-based MRI enhances the value of musculoskeletal MRI by improving patient access and comfort and promoting sustainable imaging practices. This article offers a comprehensive overview of the technical aspects, benefits, and challenges of modern accelerated musculoskeletal MRI, guiding radiologists and researchers in this evolving field.

Retrospective motion correction for preclinical/clinical magnetic resonance imaging based on a conditional generative adversarial network with entropy loss.

Multishot scan magnetic resonance imaging (MRI) acquisition is inherently sensitive to motion, and motion artifact reduction is essential for improving the image quality in MRI. This work proposes and validates a new end-to-end motion-correction method for the multishot sequence that incorporates a conditional generative adversarial network with minimum entropy (cGANME) of MR images. The cGANME contains an encoder-decoder generator to obtain motion-corrected images and a PatchGAN discriminator to classify the image as either real (motion-free) or fake (motion-corrected). The entropy of the images is set as one loss item in the cGAN's loss as the entropy increases monotonically with the motion artifacts. An ablation experiment of the different weights of entropy loss was performed to evaluate the function of entropy loss. The preclinical dataset was acquired with a fast spin echo pulse sequence on a 7.0-T scanner. After the simulation, we had 10,080/2880/1440 slices for training, testing, and validating, respectively. The clinical dataset was downloaded from the Human Connection Project website, and 11,300/3500/2000 slices were used for training, testing, and validating after simulation, respectively. Extensive experiments for different motion patterns, motion levels, and protocol parameters demonstrate that cGANME outperforms traditional and some state-of-the-art, deep learning-based methods. In addition, we tested cGANME on in vivo awake rats and mitigated the motion artifacts, indicating that the model has some generalizability.

Comparison between T2-weighted two-dimensional and three-dimensional fast spin-echo MRI sequences for characterizing thoracolumbar intervertebral disc disease in small-breed dogs.

Magnetic resonance imaging (MRI) is a standard test for diagnosis and treatment planning in dogs with degenerative thoracolumbar intervertebral disc disease (IVDD). However, published studies evaluating three-dimensional fast-spin echo (3D-FSE) pulse sequences for dogs with IVDD are currently limited. Aims of this retrospective, observational study were to compare findings from T2-weighted two- and three-dimensional fast spin-echo sequences (2D- and 3D-FSE, respectively) for a group of small breed dogs with thoracolumbar IVDD. Inclusion criteria were dogs with IVDD that underwent 1.5-Tesla MRI using both 2D-FSE and 3D-FSE sequences. For each dog and sequence, five pathologic indices were recorded: epidural fat discontinuation, vertebral canal compromise, spinal cord signal change, disc degeneration, and nerve root compression. Two independent investigators also scored visibility of the facet joint, intervertebral foramen, nerve roots, spinal cord grey-white matter differentiation, intervertebral discs, and epidural fat. The Wilcoxon signed-rank test was used to evaluate the between-sequence differences in pathologic indices and visibility scores. Interobserver agreement was measured using Cohen's weighted kappa along with 95% confidence intervals. A total of 21 dogs were sampled. The 3D-FSE sequences had higher pathologic indices of vertebral canal compromise (P=0.020) and spinal cord signal change (P=0.046) than 2D-FSE sequences. Furthermore, 3D-FSE sequences had higher visibility scores for the facet joint, intervertebral foramen, and nerve root structures (P<0.001). Findings from the current supported the use of 3D-FSE sequences over 2D-FSE sequences for the evaluation of IVDD and visualization of spinal structures in small breed dogs.

Reducing “slice cross-talk” effect in metamaterial assisted fast spin-echo MRI

Imaging of subtle changes in hand structures is challenged by the limited image quality, especially at 1.5 T. Reduction of specific absorption rate in metamaterial-assisted 1.5 T MRI provides an opportunity to utilize efficient pulse sequences and to improve the quality of acquired images. This work is devoted to the assessment of potential improvements of slice selectivity and reducing a ”slice cross-talk” artifact, using fast spin-echo (FSE) pulse sequence together with a metamaterial-based coil. The slice selection in conventional T1-weighted FSE wrist imaging pulse sequences was modeled using a ”Bloch Equations Simulator”. Two types of pulses were compared: apodized SINC pulses (reference) common for clinical FSE, and optimized selective Shinnar–Le Roux (SLR) pulses constructed in the MATPULSE program. Regular and SLR-based FSE pulse sequences were tested in a phantom experiment with different gaps between slices to investigate the “slice cross-talk” artifact presence. Combining the utilization of the metamaterial-based coil with an SLR-based FSE provided 28 times lower energy deposition in a duty cycle, as compared to the regular FSE with a conventional transmit coil. When the slice gap was decreased from 100% to 0%, the “slice cross-talk” effect reduced the signal intensity by 16%-18% in the SLR-based FSE and by 23%-32% for the regular FSE. The use of SLR pulses together with the metamaterial-based coil allowed to reduce the ”slice cross-talk” effect in contiguous FSE, while still being within the safe SAR limits.

Comparative analysis of SINC-shaped and SLR pulses performance for contiguous multi-slice fast spin-echo imaging using metamaterial-based MRI.

To comparatively assess the performance of highly selective pulses computed with the SLR algorithm in fast-spin echo (FSE) within the current radiofrequency safety limits using a metamaterial-based coil for wrist magnetic resonance imaging. Apodized SINC pulses commonly used for clinical FSE sequences were considered as a reference. Selective SLR pulses with a time-bandwidth product of four were constructed in theMATPULSE program. Slice selection profiles in conventional T1-weighted and PD-weighted FSE wrist imaging pulse sequences were modeled using a Bloch equations simulator. Signal evolution was assessed in three samples with relaxation times equivalent to those in musculoskeletal tissues at 1.5T. Regular and SLR-based FSE pulse sequences were tested in a phantom experiment in a multi-slice mode with different gaps between slices and the direct saturation effect was investigated. As compared to the regular FSEs with a conventional transmit coil, combining the utilization of the metadevice with SLR-based FSEs provided a 23 times lower energy deposition in a duty cycle. When the slice gap was decreased from 100 to 0%, the "slice cross-talk" effect reduced the signal intensity by 15.9-17.6% in the SLR-based and by 22.9-32.3% in the regular T1-weighted FSE; and by 0.0-6.4% in the SLR-based and by 0.3-9.3% in the regular PD-weighted FSE. SLR-based FSE together with the metadevice allowed to increase the slice selectivity while still being within the safe SAR limits. The "slice cross-talk" effects were conditioned by the number of echoes in the echo train, the repetition time, and T1 relaxation times. The approach was more beneficial for T1-weighted SLR-based FSE as compared to PD-weighted. The combination of the metadevice and SLR-based FSE offers a promising alternative for MR investigations that require scanning in a "Low-SAR" regime such as those for children, pregnant women, and patients with implanted devices.

3D MRI of the Ankle: A Concise State-of-the-Art Review.

Magnetic resonance imaging (MRI) is a powerful imaging modality for visualizing a wide range of ankle disorders that affect ligaments, tendons, and articular cartilage. Standard two-dimensional (2D) fast spin-echo (FSE) and turbo spin-echo (TSE) pulse sequences offer high signal-to-noise and contrast-to-noise ratios, but slice thickness limitations create partial volume effects. Modern three-dimensional (3D) FSE/TSE pulse sequences with isotropic voxel dimensions can achieve higher spatial resolution and similar contrast resolutions in ≤ 5 minutes of acquisition time. Advanced acceleration schemes have reduced the blurring effects of 3D FSE/TSE pulse sequences by affording shorter echo train lengths. The ability for thin-slice partitions and multiplanar reformation capabilities eliminate relevant partial volume effects and render modern 3D FSE/TSE pulse sequences excellently suited for MRI visualization of several oblique and curved structures around the ankle. Clinical efficiency gains can be achieved by replacing two or three 2D FSE/TSE sequences within an ankle protocol with a single isotropic 3D FSE/TSE pulse sequence. In this article, we review technical pulse sequence properties for 3D MRI of the ankle, discuss practical considerations for clinical implementation and achieving the highest image quality, compare diagnostic performance metrics of 2D and 3D MRI for major ankle structures, and illustrate a broad spectrum of ankle abnormalities.

Rapid Musculoskeletal MRI in 2021: Clinical Application of Advanced Accelerated Techniques.

OBJECTIVE. The purpose of this article is to provide a practice-focused review of the clinical application of advanced acceleration techniques for rapid musculoskeletal MRI examinations. CONCLUSION. Parallel imaging, simultaneous multislice acquisition, compressed sensing-based sampling, and synthetic MRI techniques provide unprecedented opportunities for rapid musculoskeletal MRI examinations. For 2D and 3D fast spin-echo and turbo spin-echo pulse sequences, acceleration factors between 3 and 8 can be realized in clinical practice, amounting to a time savings of 66-85% when compared with unaccelerated acquisitions.

Reducing PNS with minimal performance penalties via simple pulse sequence modifications on a high-performance compact 3T scanner

One of the major concerns associated with high-performance gradients is peripheral nerve stimulation (PNS) of the subject during MRI exams. Since the installation, more than 680 volunteer subjects (patients and controls) have been scanned on a compact 3 T MRI system with high-performance gradients, capable of 80 mT m−1 gradient amplitude and 700 T m−1 s−1 slew rate simultaneously. Despite PNS concerns associated with the high-performance gradients, due to the smaller physical dimensions of the gradient coils, minimal or no PNS sensation was reported with most pulse sequences. The exception was PNS reported by only five of 252 subjects (about 2%) scanned with a specific 3D fast spin echo pulse sequence (3DFLAIR). Rather than derating the entire system performance across all pulse sequences and all gradient lobes, we addressed reported PNS effect with a simple and specific modification to the targeted lobes of the problematic pulse sequence. in addition, the PNS convolutional model was adapted to predict sequence-specific PNS threshold level and its reduction after derating. The effectiveness of the targeted pulse sequence modification was demonstrated by successfully re-scanning four of the subjects who previously reported PNS sensations without further reported PNS. The pulse sequence modification did not result in noticeable degradation of image quality or substantial increase in scan time. The results demonstrated that PNS was rarely reported on the compact 3 T, and when it was, utilizing a specific modification of the gradient waveform causing PNS was an effective strategy, rather than derating the performance of the entire gradient system.

Comparison of the Signal-to-Noise Ratio and the Geometric Accuracy between Conventional-Magnetic Bore and Wide-Magnetic Bore 3-T Magnetic Resonance Imaging

In this study, we compared the signal-to-noise ratio (SNR) and the geometric accuracy between conventional-bore and wide-bore 3-T magnetic resonance imaging (MRI) by using both balanced fast field echo (bFFE) and turbo spin-echo (TSE) pulse sequences with a large field of view (FOV). A large-diameter phantom was scanned using clinical 60-cm conventional-bore and 70-cm wide-bore scanners. The signal-to-noise ratios (SNRs) of both the bFFE and the TSE pulse sequences were calculated for each MR scanner for various acceleration factors (AFs). The diameter of the phantom was measured in four directions to evaluate the geometric accuracy. The SNR values were found to increase as the FOV increased for both the conventional- and the wide-bore scanners. No statistically significant differences in the SNR and the geometric accuracy were observed in either sequences between the two bores (p > 0.05), although the image noise tended to increase as the AF of both bores increased. Wide-bore MRI using a large FOV can provide a SNR and a geometric accuracy comparable to those of conventional-bore MRI, despite the increase in the image noise as the AF of both bores is increased.

Passive Shield Structure to Reduce Acoustic Noise Around Magnetic Resonance Imaging Device and Prevent Deterioration of Images

A spatial arrangement of passive shield copper rings which prevents the deterioration of tomographic image was proposed to reduce acoustic noise around magnetic resonance imaging (MRI) devices. Tests for the copper rings, the conventional copper shield, and the non-shielded structures were conducted to compare the sound level in four kinds of pulse sequences and image quality in the fast spin echo (FSE) pulse sequence with a clinical 1.5 T MRI system. Numerical analyses revealed the influences of the electromagnetic force and unnecessary magnetic field caused by the eddy current. For the copper ring structures, the sound level outside the magnet decreased 5 dB(A) from that of the non-shielded structure. The percentages of image deterioration number in the FSE pulse sequence for the conventional and the copper ring structures were increased 15% and decreased 4%, respectively. Numerical results showed that the electromagnetic force of the MRI devices decreased 60% and the unnecessary magnetic field at the imaging space decreased 30%, supporting the test results. The position of the eddy current was the most important factor for each contribution. The proposed copper ring structure is able to reduce acoustic noise outside the magnet and prevent image deterioration.

A multi-band double-inversion radial fast spin-echo technique for T2 cardiovascular magnetic resonance mapping of the heart

BackgroundDouble inversion recovery (DIR) fast spin-echo (FSE) cardiovascular magnetic resonance (CMR) sequences are used clinically for black-blood T2-weighted imaging. However, these sequences suffer from slice inefficiency due to the non-selective inversion pulses. We propose a multi-band (MB) encoded DIR radial FSE (MB-DIR-RADFSE) technique to simultaneously excite two slices. This sequence has improved signal-to-noise ratio per unit time compared to a single slice excitation. It is also motion robust and enables the reconstruction of high-resolution black-blood T2-weighted images and T2 maps for the excited slices.MethodsHadamard encoded MB pulses were used in MB-DIR-RADFSE to simultaneously excite two slices. A principal component based iterative reconstruction was used to jointly reconstruct black-blood T2-weighted images and T2 maps. Phantom and in vivo experiments were performed to evaluate T2 mapping performance and results were compared to a T2-prepared balanced steady state free precession (bSSFP) method. The inter-segment variability of the T2 maps were assessed using data acquired on healthy subjects. A reproducibility study was performed to evaluate reproducibility of the proposed technique.ResultsPhantom experiments show that the T2 values estimated from MB-DIR-RADFSE are comparable to the spin-echo based reference, while T2-prepared bSSFP over-estimated T2 values. The relative contrast of the black-blood images from the multi-band scheme was comparable to those from a single slice acquisition. The myocardial segment analysis on 8 healthy subjects indicated a significant difference (p-value < 0.01) in the T2 estimates from the apical slice when compared to the mid-ventricular slice. The mean T2 estimate from 12 subjects obtained using T2-prepared bSSFP was significantly higher (p-value = 0.012) compared to MB-DIR-RADFSE, consistent with the phantom results. The Bland-Altman analysis showed excellent reproducibility between the MB-DIR-RADFSE measurements, with a mean T2 difference of 0.12 ms and coefficient of reproducibility of 2.07 in 15 clinical subjects. The utility of this technique is demonstrated in two subjects where the T2 maps show elevated values in regions of pathology.ConclusionsThe use of multi-band pulses for excitation improves the slice efficiency of the double inversion fast spin-echo pulse sequence. The use of a radial trajectory and a joint reconstruction framework allows reconstruction of TE images and T2 maps for the excited slices.

Body diffusion-weighted imaging using magnetization prepared single-shot fast spin echo and extended parallel imaging signal averaging.

This work demonstrates a magnetization prepared diffusion-weighted single-shot fast spin echo (SS-FSE) pulse sequence for the application of body imaging to improve robustness to geometric distortion. This work also proposes a scan averaging technique that is superior to magnitude averaging and is not subject to artifacts due to object phase. This single-shot sequence is robust against violation of the Carr-Purcell-Meiboom-Gill (CPMG) condition. This is achieved by dephasing the signal after diffusion weighting and tipping the MG component of the signal onto the longitudinal axis while the non-MG component is spoiled. The MG signal component is then excited and captured using a traditional SS-FSE sequence, although the echo needs to be recalled prior to each echo. Extended Parallel Imaging (ExtPI) averaging is used where coil sensitivities from the multiple acquisitions are concatenated into one large parallel imaging (PI) problem. The size of the PI problem is reduced by SVD-based coil compression which also provides background noise suppression. This sequence and reconstruction are evaluated in simulation, phantom scans, and in vivo abdominal clinical cases. Simulations show that the sequence generates a stable signal throughout the echo train which leads to good image quality. This sequence is inherently low-SNR, but much of the SNR can be regained through scan averaging and the proposed ExtPI reconstruction. In vivo results show that the proposed method is able to provide diffusion encoded images while mitigating geometric distortion artifacts compared to EPI. This work presents a diffusion-prepared SS-FSE sequence that is robust against the violation of the CPMG condition while providing diffusion contrast in clinical cases. Magn Reson Med 79:3032-3044, 2018. © 2017 International Society for Magnetic Resonance in Medicine.

Adenoviral vector mediated ferritin over-expression in mesenchymal stem cells detected by 7T MRI in vitro

ObjectiveThe aim of the present work was to verify whether adenoviral vector mediated ferritin over-expression in mesenchymal stem cells could be detected by 7T MRI device, and to explore the relationship between ferritin content and MRI signal intensities.MethodsA recombined adenoviral vector (rAdV) encoding ferritin heavy chain (FTH1) subunit was specially designed for the aim of infecting bone marrow mesenchymal stem cells (BMSCs). Ferritin over-expression in BMSCs was determined by cell immunocytochemistry and the ferritin content in cells was determined by ELISA assay. BMSCs were subjected to cell viability, proliferation and multi-differentiation analyses as well as 7T MRI test using fast spin-echo pulse sequence. The R2 value andδR2 were calculated according to T2 mapping images.ResultsAs was confirmed by cell immunocytochemistry and ELISA assay, rAdV mediated ferritin was over-expressed in BMSCs. Ferritin over-expression did not interfere with stem cell viability or pluripotent differentiation but slowed cell proliferation. The R2 value of BMSCs-FTH1 vs control BMSCs from 1–4 weeks was16.65±1.28 s-1 vs 13.99±0.80 s-1, (t = 3.94, p = 0.004), 15.63±1.37 s-1 vs 13.87±0.83 s-1 (t = 2.47, p = 0.039), 15.53±0.88 s-1 vs 14.25±0.53 s-1 (t = 2.80, p = 0.023) and 14.61±1.28 s-1 vs 13.69±1.03 s-1 (t = 1.25, p = 0.24), respectively. δR2 gradually decreased from 1–4 weeks and the difference between the groups had statistical significance (F = 12.45, p<0.01).δR2 was positively correlated with OD value (r = 0.876, p<0.01) and ferritin concentration (r = 0.899, p<0.01) as determined by Pearson correlation.ConclusionsOur study confirms that ferritin could be over-expressed in BMSCs as a result of rAdV mediated infection and could be quantitatively detected by 7T MRI device. The differences in T2 signal intensities and R2 values stem from internal contrast generated by endogenous ferritin over-expression. The correlation between δR2, OD and ferritin concentration suggests that MRI can detect ferritin signal change accurately.

SINGLE-SHOT TURBO SPIN ECHO PULSE SEQUENCE FINDINGS IN DOGS WITH AND WITHOUT PROGRESSIVE MYELOMALACIA.

Progressive myelomalacia is an uncommon type of ischemic, hemorrhagic spinal cord infarction. Diagnosis can be difficult, but prompt recognition is important. We hypothesized that cerebrospinal fluid signal attenuation on magnetic resonance (MR) images would be more extensive in dogs that developed progressive myelomalacia vs. control dogs. A retrospective analytic cohort study was designed. Dogs were included if they presented for acute paraplegia and loss of deep pain perception and had undergone MR imaging using both sagittal single-shot turbo spin echo (SSTSE) and standard sagittal T2-weighted fast spin echo (T2W) pulse sequences. Dogs were divided into progressive myelomalacia and control groups for comparisons. All MR examinations were evaluated by three reviewers blinded to patient outcome. Length of cerebrospinal fluid attenuation was recorded as a ratio to the length of the L2 vertebral body in SSTSE and T2W sequences (CSF:L2SSTSE and CSF:L2T2 , respectively). Length of intramedullary spinal cord hyperintensity was recorded as a ratio to the length of the L2 vertebral body in T2W sequences. A total of 21 dogs were included (five in the progressive myelomalacia group and 16 in the control group). The mean CSF:L2SSTSE attenuation value was significantly higher in dogs that developed progressive myelomalacia (CSF:L2SSTSE = 10.7) compared to controls (CSF:L2SSTSE = 5.4; P = 0.015). A cut off ratio of attenuation >7.4 provided optimal differentiation between groups in this study. Findings supported the conclusion that dogs with CSF:L2SSTSE ≤ 7.4 are unlikely to develop progressive myelomalacia while dogs with CSF:L2SSTSE > 7.4 are indeterminate for progressive myelomalacia.

Global and Regional Brain Assessment with Quantitative MR Imaging in Patients with Prior Exposure to Linear Gadolinium-based Contrast Agents.

Purpose To assess the association of global and regional brain relaxation times in patients with prior exposure to linear gadolinium-based contrast agents (GBCAs). Materials and Methods The institutional review board approved this cross-sectional study. Thirty-five patients (nine who had received GBCA gadopentetate dimeglumine injections previously [one to eight times] and 26 patients who did not) who underwent brain magnetic resonance (MR) imaging with a mixed fast spin-echo pulse sequence were assessed. The whole brain was segmented according to white and gray matter by using a dual-clustering algorithm. In addition, regions of interest were measured in the globus pallidus, dentate nucleus, thalamus, and pons. The Mann-Whitney U test was used to assess the difference between groups. Multiple regression analysis was performed to assess the association of T1 and T2 with prior GBCA exposure. Results T1 values of gray matter were significantly shorter for patients with than for patients without prior GBCA exposure (P = .022). T1 of the gray matter of the whole brain (P < .001), globus pallidus (P = .002), dentate nucleus (P = .046), and thalamus (P = .026) and T2 of the whole brain (P = .004), dentate nucleus (P = .023), and thalamus (P = .002) showed a significant correlation with the accumulated dose of previous GBCA administration. There was no significant correlation between T1 and the accumulated dose of previous GBCA injections in the white matter (P = .187). Conclusion Global and regional quantitative assessments of T1 and T2 demonstrated an association with prior GBCA exposure, especially for gray matter structures. The results of this study confirm previous research findings that there is gadolinium deposition in wider distribution throughout the brain. © RSNA, 2016 Online supplemental material is available for this article.

Magnetic resonance imaging in pediatric appendicitis: a systematic review.

Magnetic resonance imaging for the evaluation of appendicitis in children has rapidly increased recently. This change has been primarily driven by the desire to avoid CT radiation dose. This meta-analysis reviews the diagnostic performance of MRI for pediatric appendicitis and discusses current knowledge of cost-effectiveness. We used a conservative Haldane correction statistical method and found pooled diagnostic parameters including a sensitivity of 96.5% (95% confidence interval [CI]: 94.3-97.8%), specificity of 96.1% (95% CI: 93.5-97.7%), positive predictive value of 92.0% (95% CI: 89.3-94.0%) and negative predictive value of 98.3% (95% CI: 97.3-99.0%), based on 11 studies. Assessment of patient outcomes associated with MRI use at two institutions indicates that time to antibiotics was 4.7h and 8.2h, time to appendectomy was 9.1h and 13.9h, and negative appendectomy rate was 3.1% and 1.4%, respectively. Alternative diagnoses were present in ~20% of cases, most commonly adnexal cysts and enteritis/colitis. Regarding technique, half-acquisition single-shot fast spin-echo (SSFSE) pulse sequences are crucial. While gadolinium-enhanced T1-weighted pulse sequences might be helpful, any benefit beyond non-contrast MRI has not been confirmed. Balanced steady-state free precession (SSFP) sequences are generally noncontributory. Protocols do not need to exceed five sequences; four-sequence protocols are commonly utilized. Sedation generally is not indicated; patients younger than 5years might be attempted based on the child's ability to cooperate. A comprehensive pediatric cost-effectiveness analysis that includes both direct and indirect costs is needed.

Possibility Study of Scale Invariant Feature Transform (SIFT) Algorithm Application to Spine Magnetic Resonance Imaging.

The purpose of this study is an application of scale invariant feature transform (SIFT) algorithm to stitch the cervical-thoracic-lumbar (C-T-L) spine magnetic resonance (MR) images to provide a view of the entire spine in a single image. All MR images were acquired with fast spin echo (FSE) pulse sequence using two MR scanners (1.5 T and 3.0 T). The stitching procedures for each part of spine MR image were performed and implemented on a graphic user interface (GUI) configuration. Moreover, the stitching process is performed in two categories; manual point-to-point (mPTP) selection that performed by user specified corresponding matching points, and automated point-to-point (aPTP) selection that performed by SIFT algorithm. The stitched images using SIFT algorithm showed fine registered results and quantitatively acquired values also indicated little errors compared with commercially mounted stitching algorithm in MRI systems. Our study presented a preliminary validation of the SIFT algorithm application to MRI spine images, and the results indicated that the proposed approach can be performed well for the improvement of diagnosis. We believe that our approach can be helpful for the clinical application and extension of other medical imaging modalities for image stitching.

Three-dimensional isotropic fast spin-echo MR lymphangiography of T1-weighted and intermediate-weighted pulse sequences in patients with lymphoedema

To evaluate the feasibility of magnetic resonance (MR) lymphangiography acquired using three-dimensional (3D) isotropic T1-weighted fast spin-echo (FSE) and 3D isotropic intermediate-weighted FSE sequences, as the new method of MR lymphangiography, and to compare the results of these two methods in patients with lymphoedema. Thirty-three extremities of 27 patients with primary or secondary lymphoedema and who had undergone radionuclide lymphoscintigraphy and MR lymphangiography with 3D isotropic T1-weighted FSE and 3D isotropic intermediate-weighted FSE were included in the study. The results of both imaging techniques were independently reviewed by two readers in consensus who rated the lymphatic drainage pattern, the quality of the depiction of lymphatic vessels and lymph nodes, and the level of lymph vessel enhancement. The assessment scores of each imaging sequence were compared using the Wilcoxon signed-rank test. The results were expressed as means with standard deviations. More lymphatic vessels were visualised on T1-weighted FSE than on intermediate-weighted FSE (p<0.001). As more lymphatic vessels were detected on T1-weighted FSE, the per-extremity grade of the lymphatic drainage pattern was higher (p=0.046) and the visible levels of lymph-vessel enhancement were also significantly higher (p=0.004) on the T1-weighted FSE sequence, whereas the conspicuity of lymph nodes was superior on intermediate-weighted FSE (p=0.004). MR lymphangiography using the 3D FSE pulse sequence is a feasible and noticeable new technique of MR lymphangiography. Between the two applicable protocols used, T1-weighted FSE provided better information regarding lymphatic vessels and their drainage, whereas intermediate-weighted FSE has the advantage of depicting lymph nodes in lymphoedematous extremities.

0113: Cardiac magnetic resonance T1 mapping pre and post contrast in heart transplant patients with clinical antibody-mediated rejection: a preliminary experience

Antibody-mediated rejection (AMR) is characterized by histopathological and immunophenotypic findings such as activated endothelial cells, intravascular macrophages and evidence of capillary C4d deposition. This inflammatory reaction could be followed by diffuse fibrosis. Cardiac magnetic resonance (CMR) with recently T1 mapping is a promising technique to identify diffuse myocardial fibrosis. The purpose of this study was to assess T1 mapping in patients with AMR. 2 patients with clinical AMR (histopathological and immunophenotypic findings, presence of donor-specific allo antibodies and allograft dysfunction) performed a CMR study one week (for the first patient) and 3 weeks (for the second patient) after the treatment of AMR (plasmapheresis, IV Immunoglobulins and Rituximab). Images were acquired on a 1.5 Tesla scanner (Siemens) including T1 mapping using a shortened modified look-locker inversion-recovery sequence and T2 mapping in a matched mid-ventricular short axis slice using a black- blood single shot fast spin echo pulse sequence. Segmental and global T1 values were measured before and 15 minutes after administration of 0.2 mmol/kg of Gadoteric acid and compared to our cohort of 17 controls. Mean non contrast T1 values were significantly higher in heart transplants patients compared to controls (1100±5ms vs 947±29ms, P<0.001). Segmental T1 values were significantly higher in the 6 regions of interest compared to controls (P <0.001 in all segments). Mean post contrast T1 values were not significantly different in patients and controls. Mean T2 value was higher in patients compared to controls (73±13 vs 50± 4ms), suggesting the presence of global edema. Heart transplant patients with clinical antibody-mediated rejection show a significant increased global and segmental non contrast T1 values suggesting the presence of diffuse myocardial fibrosis. Further studies are required to confirm these data.

Fast T2 mapping with multiple echo, Caesar cipher acquisition and model-based reconstruction.

Fast, quantitative T2 mapping is of value to both clinical and research environments. However, many protocols utilizing fast spin echo (FSE) pulse sequences contain acceleration-induced artifacts that are compounded when fitting parameter maps, especially in the presence of imperfect refocusing. This work presents a B1 -corrected, model-based reconstruction and associated Cartesian FSE phase-encode ordering that provides enhanced accuracy in T2 estimates compared with other common accelerated protocols. The method, known as multiple echo, Caesar cipher acquisition and model-based reconstruction (ME-CAMBREC), directly fitted T2 , flip angle, and proton density maps on a row-by-row basis to k-space data using the extended phase graph model. Regularization was enforced in order to minimize noise amplification effects. ME-CAMBREC was evaluated in computational and physical phantoms, as well as human brain, and compared with other FSE-based T2 mapping protocols, DESPOT2, and parallel imaging acceleration. In computational, phantom, and human experiments, ME-CAMBREC provided T2 maps with fewer artifacts and less or similar error compared with other methods tested at moderate-to-high acceleration factors. In vivo, ME-CAMBREC provided error rates approximately one-half those of other methods. Directly fitting multi-echo data to k-space using the extended phase graph can increase fidelity of T2 maps significantly, especially when using an appropriate phase-encode ordering.