Conventional Spin-echo Techniques Research Articles

A Fast Magnetic Flux Density Measurement Method With Skip-Echo Acquired Turbo Spin Echo (SATE).

The measurements of magnetic flux density ( Bz) needed in magnetic resonance electrical impedance tomography (MREIT) and magnetic resonance current density imaging (MRCDI) techniques often utilize spin echo (SE)-based sequences for data acquisition. The low imaging speed of SE-based methods significantly hampers the clinical applications of MREIT and MRCDI. Here, we propose a new sequence for substantially accelerating the acquisition of Bz measurements. A skip-echo acquired turbo spin echo (SATE) imaging sequence based on the conventional turbo spin echo (TSE) technique was proposed by adding a skip-echo module in front of the TSE acquisition module. The skip-echo module consisted of a series of refocusing pulses without acquisition. In SATE, amplitude-modulated crusher gradients were used to remove the stimulated echo pathways, and the radiofrequency (RF) pulse shape was specially selected to preserve more signals. In efficiency evaluation experiments performed on a spherical gel phantom, we demonstrated that SATE had improved measurement efficiency compared to the conventional TSE sequence via skipping one echo before acquiring signals. The accuracy of the Bz measurements by SATE was validated against those by the multi-echo injection current nonlinear encoding (ME-ICNE) method, while SATE was able to accelerate the data acquisition up to 10-fold. Volumetric coverage of Bz maps obtained in the phantom, pork, and human calf illustrated that SATE can reliably measure volumetric Bz distributions within clinically acceptable time. The proposed SATE sequence provides a fast and effective approach for volumetric coverage of Bz measurements, greatly facilitating the clinical applications of MREIT and MRCDI techniques.

Morfometrijsko-anatomski parametri interkondilarne jame kolena kod odraslih osoba u Srbiji

Objective: The aim of this investigation was to examine normal intercondylar notch morphometry in Serbian population and to determine whether there are gender differences in anatomical parameters of the intercondylar notch among asymptomatic subjects without structural change. Method: The study included Mr images of 90 patients (45 men and 45 women) receiving a 1,5-T knee scan at our radiological institute after the approval from the Ethics committee, which were taken in the period from 2010 to 2017. The knee was placed in the neutral position, and Mr images were obtained using conventional spin echo techniques. The morphology of the intercondylar notch (Ushaped and A-shaped notch) was measured for each knee. Results: The measurements of parameters for intercondylar notch geometry were obtained by analyzing coronal Mr images. U-shaped intercondylar notch was found in 46 patients (51.2%) and A-shaped intercondylar notch in 44 (48.8%). There was no significant difference in the shape incidence in Serbian population (p>0.05). According to the Notch width index (NWI) and the Notch shape index (NSI) criteria, we found U-shaped intercondylar notch with 24 men and 22 women and A-shaped intercondylar notch with 23 men and 21 women. There was no significant difference in incidence between the genders (p>0.05). Conclusion: We concluded that for all examined anatomical parameters of the intercondylar notch there were no significant differences in Serbian population. According to our findings in this study, we concluded that there was no sexual dimorphism for anatomical parameters of intercondylar notch in Serbian population.

Multiple Sclerosis: Comparison of the Conventional Spin-Echo T2-Weighted and Flair Techniques Through Image Processing

Multiple Sclerosis: Comparison of the Conventional Spin-Echo T2-Weighted and Flair Techniques Through Image Processing

T1-Weighted Magnetic Resonance Carotid Plaque Imaging: a Comparison between Conventional and Fast Spin-Echo Techniques

Magnetic resonance imaging is widely used to evaluate the intraplaque components of the cervical carotid artery. The non-gated T1-weighted spin-echo (SE) technique has been reported to have an excellent ability for discriminating stable and unstable plaques. However, the diagnostic performance of various SE-based techniques remains unclear. Hence, we compared plaque signals obtained by 3 kinds of SE-based methods with histological findings. We prospectively examined 40 patients who underwent carotid endarterectomy by using 1.5-T scanners and obtained 2-dimensional (2D) conventional spin-echo (CSE), 2D fast spin-echo (FSE), and 3-dimensional (3D)-FSE images with identical repetition times. We calculated contrast ratios (CRs) of the plaques against adjacent muscles and compared these values with the pathological classification of the specimens. The CRs of type VII-VIII (calcific/fibrous), IV-V (lipid-rich/necrotic), and VI (complex/hemorrhagic) plaques were significantly different between all the methods (P <.001) and were discriminated from each other at sensitivities of 83%-100% and specificities of 94%-100%. The CRs of type IV-V plaques significantly differed between the methods (low to high, 2D-FSE, 2D-CSE, and 3D-FSE; P <.05); those of the type VI plaques were significantly lower with the 2D-FSE method than with the other methods (P <.01). The SE-based T1-weighted images can readily discriminate plaque characteristics with high sensitivities and specificities, although the signal intensity of unstable plaques was significantly high on the 3D-FSE images and significantly low on the 2D-FSE images.

RESPECT: Neutron resonance spin-echo spectrometer for extreme studies

We propose the design of a REsonance SPin-echo spECtrometer for exTreme studies, RESPECT, that is ideally suited for the exploration of non-dispersive processes such as diffusion, crystallization, slow dynamics, tunneling processes, crystal electric field excitations, and spin fluctuations. It is a variant of the conventional neutron spin-echo technique (NSE) by (i) replacing the long precession coils by pairs of longitudinal neutron spin-echo coils combined with RF-spin flippers and (ii) by stabilizing the neutron polarization with small longitudinal guide fields that can in addition be used as field subtraction coils thus allowing to adjust the field integrals over a range of 8 orders of magnitude. Therefore, the dynamic range of RESPECT can in principle be varied over 8 orders of magnitude in time, if neutrons with the required energy are made available. Similarly as for existing NSE-spectrometers, spin echo times of up to approximately 1μs can be reached if the divergence and the correction elements are properly adjusted. Thanks to the optional use of neutron guides and the fact that the currents for the correction coils are much smaller than in standard NSE, intensity gains of at least one order of magnitude are expected, making the concept of RESPECT also competitive for operation at medium flux neutron sources. RESPECT can also be operated in a MIEZE configuration allowing the investigation of relaxation processes in depolarizing environments as they occur when magnetic fields are applied at the sample position, i.e. for the investigation of the dynamics of flux lines in superconductors, magnetic fluctuations in ferromagnetic materials, and samples containing hydrogen.

Meniscal tears: comparison of the conventional spin-echo and fast spin-echo techniques through image processing

BackgroundConventional spin-echo (PD-CSE) and fast spin-echo (PD-FSE) techniques are frequently used to detect meniscal tears. However, the time delay for imaging with PD-CSE has resulted in its replacement with faster techniques, such as proton density fast spin-echo (PD-FSE), which has become a frequent tool at most diagnostic centres.Qualitative analysis shows that the PD-CSE technique is more sensitive, but other authors have not found significant differences between the aforementioned techniques. Therefore, we performed a quantitative analysis in this study that aims to measure differences in the quality of the images obtained with both techniques.MethodsWe compared the PD-CSE and PD-FSE techniques by quantitatively analysing the obtained proton density images: the area shown, as well as the brightness and lesion contrast of the obtained image.A set of 100 images from 50 patients thought to contain meniscal tears of the knee were selected. These 100 images were obtained from all individuals using both the PD-CSE and PD-FSE techniques. The images were processed using software developed in Delphi. In addition to these quantifications, three physicians, who are specialists in radiology and capable of analysing magnetic resonance (MR) images of the musculoskeletal system, qualitatively analysed the diagnostic sensitivity of both techniques.ResultsOn average, samples obtained via the PD-CSE technique contained 22% more pixels in the lesion area. The contrast differed by 28%, and the brightness differed by 31%. The two techniques were correlated using Student’s t-test, which showed a statistically significant difference. The specialists detected meniscal tears in 30 of the images obtained via the PD-CSE technique, while only 72% of these cases were detected via the PD-FSE technique.ConclusionsThe PD-CSE technique was shown to be superior to PD-FSE for all of the evaluated properties, making its selection preferable.

Morphology of the Cartilaginous Endplates in Human Intervertebral Disks with Ultrashort Echo Time MR Imaging

To image human disk-bone specimens by using conventional spin-echo (SE) and ultrashort echo time (TE) techniques, to describe the morphology at magnetic resonance (MR) imaging, and to identify tissue components contributing to high signal intensity near the cartilaginous endplates (CEPs). This study was exempt from institutional review board approval, and informed consent was not required. Five cadaveric lumbar spines (mean age, 61 years ± 11) were prepared into six sample types containing different combinations of disk, uncalcified CEP, calcified CEP, and subchondral bone components and were imaged with proton density-weighted SE (repetition time msec/TE msec, 2000/15) and ultrashort TE (300/0.008, 6.6, echo-subtraction) sequences. Images were evaluated to determine the presence of intermediate-to-high signal intensity in regions excluding the bone marrow. Logistic regression was used to determine which tissue components were significant predictors of the presence of signal intensity for each MR technique. On ultrashort TE MR images, intact disk/uncalcified CEP/calcified CEP/bone samples exhibited bilaminar intermediate-to-high signal intensity in the region near the CEP, consistent with the histologic appearance of uncalcified and calcified CEPs. Conversely, proton density-weighted SE images exhibited low signal intensity in this region. Results of logistic regression suggested that the presence of uncalcified CEP (P = .023) and calcified CEP (P = .007) in the sample were strong predictors of the presence of signal intensity on ultrashort TE images, whereas the disk was the only predictor (P < .001) of signal intensity on proton density-weighted SE images. Ultrashort TE imaging, unlike proton density-weighted SE imaging, enabled direct visualization of the uncalcified and calcified CEP. Evaluation of the morphology and identification of sources of signal intensity at ultrashort TE MR imaging provides opportunities to potentially aid in the understanding of degenerative disk disease.

MRI After Arthroplasty: Comparison of MAVRIC and Conventional Fast Spin-Echo Techniques

The goal of this study was to evaluate the quality of images obtained with a prototype imaging technique, multiacquisition variable-resonance image combination (MAVRIC), compared with fast spin-echo (FSE) images in the evaluation of patients who have undergone hip, shoulder, or knee arthroplasty. MRI with metal-artifact reduction FSE and MAVRIC sequences was performed in the care of 122 patients who had undergone 74 hip, 27 shoulder, and 21 knee arthroplasties. The FSE and MAVRIC images were subjectively graded for visualization of the synovium, prosthesis-bone interface, and hip abductors or supraspinatus tendon. The presence of synovitis, osteolysis, or supraspinatus tendon tear was recorded. Visualization of the synovium was significantly better on MAVRIC images than on FSE images of the hip (p < 0.0001), shoulder (p < 0.01), and knee (p < 0.01). Synovitis was detected only on the MAVRIC images of nine subjects (12%) who had undergone hip arthroplasty and five subjects (18%) who had undergone shoulder arthroplasty. Visualization of the periprosthetic bone was significantly better on MAVRIC images of the hip (p < 0.0001), shoulder (p < 0.0001), and knee (p < 0.01). Osteolysis was detected only on the MAVRIC images of 12 subjects (16%) who had undergone hip arthroplasty, six (22%) who had undergone shoulder arthroplasty, and five (24%) who had undergone knee arthroplasty. Visualization of the supraspinatus tendon was significantly better on MAVRIC images (p < 0.0001). Supraspinatus tendon tears in 12 subjects (44%) were detected only on MAVRIC images. MAVRIC complements the information on FSE images after arthroplasty and is a useful additional sequence, particularly when there is concern about synovitis, periprosthetic osteolysis, or the presence of a supraspinatus tendon tear.

Imaging near metal with a MAVRIC‐SEMAC hybrid

The recently developed multi-acquisition with variable resonance image combination (MAVRIC) and slice-encoding metal artifact correction (SEMAC) techniques can significantly reduce image artifacts commonly encountered near embedded metal hardware. These artifact reductions are enabled by applying alternative spectral and spatial-encoding schemes to conventional spin-echo imaging techniques. Here, the MAVRIC and SEMAC concepts are connected and discussed. The development of a hybrid technique that utilizes strengths of both methods is then introduced. The presented technique is shown capable of producing minimal artifact, high-resolution images near total joint replacements in a clinical setting.

Development of a novel optimized breathhold technique for myocardial T2 measurement in thalassemia

To develop a reproducible fast spin-echo (FSE) technique for accurate myocardial T2 measurement with application to iron overload assessment in thalassemia. An FSE sequence was developed to permit acquisition of multiple TE images in one breathhold (BH-FSE). A dynamic black-blood scheme was introduced to better cancel blood signal. A nonselective refocusing train was also adopted to suppress stimulated echoes. The optimized technique was tested on phantoms and then applied to 10 normal volunteers and 10 thalassemia patients. Interstudy reproducibility was measured on all the 20 subjects. The mean difference in T2 values was 1.7% from phantom experiments between BH-FSE and the conventional spin-echo (SE) technique. High contrast BH-FSE images were acquired from human subjects, with minimal stimulated echoes and effective blood suppression (P = 0.0005). The coefficient of variation for interstudy reproducibility was 4.3%. T2 values from thalassemia patients were substantially lower than those from the normal subjects (45.2 +/- 26.1 msec vs. 56.9 +/- 8.4 ms, P = 0.02). The dynamic black-blood T2 sequence is a fast reproducible acquisition that compares favorably with conventional techniques, is robust to motion artifacts, and yields high blood-myocardium contrast. This technique may provide a useful tool in thalassemia and other scenarios requiring myocardial T2 quantification.

Cortical layer-dependent BOLD and CBV responses measured by spin-echo and gradient-echo fMRI: Insights into hemodynamic regulation

Spatial specificity of functional magnetic resonance imaging (fMRI) signals to sub-millimeter functional architecture remains controversial. To investigate this issue, high-resolution fMRI in response to visual stimulus was obtained in isoflurane-anesthetized cats at 9.4 T using conventional gradient-echo (GE) and spin-echo (SE) techniques; blood oxygenation-level dependent (BOLD) and cerebral blood volume (CBV)-weighted data were acquired without and with injection of 10 mg Fe/kg monocrystalline iron oxide nanoparticles (MION), respectively. Studies after MION injection at two SE times show that the T 2′ contribution to SE fMRI is minimal. GE and SE BOLD changes were spread across the cortical layers. GE and SE CBV-weighted fMRI responses peaked at the middle cortical layer, which has the highest experimentally-determined microvascular volume; full-width at half-maximum was <1.0 mm. Parenchymal sensitivity of GE CBV-weighted fMRI was ∼3 times higher than that of SE CBV-weighted fMRI and ∼1.5 times higher than that of BOLD fMRI. It is well known that GE CBV-weighted fMRI detects a volume change in vessels of all sizes, while SE CBV-weighted fMRI is heavily weighted toward microvascular changes. Peak CBV change of 10% at the middle of the cortex in GE measurements was 1.8 times higher than that in SE measurements, indicating that CBV changes occur predominantly for vasculature connecting the intracortical vessels and capillaries. Our data supports the notion of laminar-dependent CBV regulation at a sub-millimeter scale.

Application of k- and q-space encoding NMR techniques on granular media in a 3D model fluidized bed reactor

A combination of PFG–NMR imaging and velocity encoding methods was applied to investigate the dynamic behavior of a bed of poppy seeds subjected to air flow, representing a model setup for fluidized bed reactors. The particle motion is described both from a statistical point of view, by determining propagators and dispersion coefficients representing an average over the whole bed volume, as well as combined with spatial resolution by generating velocity maps. Velocity images of different horizontal slices in the bed confirm the notion of a toroidal particle flow pattern inside the shallow granular bed. Despite the need of considerable averaging due to the random motion of the relatively few particles in the bed, quantitative velocity images and statistical information about the random particle motion can be obtained from monitoring the fluid component in the seeds by conventional spin-echo techniques.

The use of magnetic resonance and MR angiography in the detection of cerebral infarction: A complication of pediatric bacterial meningitis

Association of both cerebral infarction and acute bacterial meningitis is more common in younger patients than in the elderly. The rate of mortality and the frequency of sequela are very high inspite of the use of modern antibiotic therapy. In more than 30% of the cases of childhood bacterial meningitis, both arterial and venous infarctions can occur. The aim of this study was to present the role of the use of magnetic resonance (MRI), and MR angiography (MRA) in the detection of bacterial meningitis in children complicated with cerebral infarctions. In the Centre for MR, the Clinical Centre of Serbia, 25 patients with the diagnosis of bacterial meningitis, of which 9 children with cerebral infarction whose clinical condition deteriorated acutely, despite the antibiotic therapy, underwent MRI and MR angiography examination on a 1T scanner. Examination included the conventional spin-echo techniques with T1-weighted saggital and coronal, and T2- weighted axial and coronal images. Coronal fluid attenuated inversion recovery (FLAIR) and the postcontrast T1-weighted images in three orthogonal planes were also used. The use MR angiography was accomplished by the three-dimensional time-of-flight (3D TOF) technique. The findings included: multiple hemorrhagic infarction in 4 patients, multiple infarctions in 3 patients, focal infarction in 1 patient and diffuse infarction (1 patient). Common sites of involvement were: the frontal lobes, temporal lobes and basal ganglia. The majority of infarctions were bilateral. In 3 of the patients empyema was found, and in 1 patient bitemporal abscess was detected. In 8 of the patients MR angiography confirmed inflammatory vasculitis. Infarction is the most common sequela of severe meningitis in children. Since the complication of cerebral infarction influences the prognosis of meningitis, repetitive MRI examinations are very significant for the evaluation of the time course of vascular involvement. The use of MRI, especially FLAIR imaging, confirmed its value in the detection and determination of the site and the extent of cerebral infarction. Non-invasive technique of examination, 3D TOF MR angiography clearly shoud show the presence of inflammatory vasculitis.

Accuracy of MR imaging for staging prostate cancer: A meta-analysis to examine the effect of technologic change

The purpose of this study was to summarize the accuracy of magnetic resonance (MR) imaging for staging prostate cancer and to determine the effect of high magnetic field strength, use of the endorectal coil, use of fast spin-echo (SE) imaging, and study size on staging accuracy. A literature search and review yielded 27 studies comparing MR imaging to a pathologic standard in patients with clinically limited prostate cancer. Subgroup analyses examined magnetic field strength, use of an endorectal coil, use of fast SE imaging, publication date, and study size. A summary receiver operating characteristic curve for all studies had a maximum joint sensitivity and specificity of 74%. At a specificity of 80% on this curve, sensitivity was 69%. Subgroup analyses showed that fast SE imaging was statistically significantly more accurate than conventional SE techniques (P < .001). Unexpectedly, studies employing higher magnetic field strength and those employing an endorectal coil were less accurate. Seemingly small technologic advances may influence test accuracy. Early and small studies, however, may overstate accuracy because of publication bias, bias in small samples, or earlier studies being performed by the experts who developed the technology itself.

EVALUATION OF DURAL SINUS INVASION AND EXTENSION OF EXTRA-AXIAL INTRACRANIAL TUMORS. The advantages of a high-resolution postcontrast 3-D gradient-echo technique

Objective: To assess the usefulness of a postcontrast 3-D Fourier transform (3DFT) gradient-echo (GRE) technique in dural sinus invasion and extension of extraaxial intracranial tumors in comparison with a conventional spin-echo (SE) technique. Material and Methods: Fourteen consecutive patients with 15 extra-axial tumors in contiguity with the dural sinus, including 14 meningiomas and 1 adenoid cystic carcinoma, underwent postcontrast T1-weighted SE and GRE MR studies. Detectability of dural sinus invasion and extension was evaluated using two sequences by two neuroradiologists in a blinded manner and compared with surgical results. Quantitative analysis was also performed to calculate the contrast-to-noise ratio (CNR) between lesion and dural sinus on SE and GRE images. The data were analyzed statistically using a matched paired t-test. Results: In the qualitative evaluation, the detectability of dural sinus invasion in 3DFT-GRE images was superior to that using SE images. The mean CNR for all lesions was 3.86 on SE images and 5.63 on 3DFT-GRE images (p=0.03). Conclusion: For evaluation of dural sinus invasion and the extension of extra-axial tumors, postcontrast 3DFT-GRE MR images were superior to conventional SE images.

Evaluation of dural sinus invasion and extension of extra-axial intracranial tumors: The advantages of a high-resolution postcontrast 3-D gradient-echo technique

To assess the usefulness of a postcontrast 3-D Fourier transform (3DFT) gradient-echo (GRE) technique in dural sinus invasion and extension of extraaxial intracranial tumors in comparison with a conventional spin-echo (SE) technique. Fourteen consecutive patients with 15 extra-axial tumors in contiguity with the dural sinus, including 14 meningiomas and 1 adenoid cystic carcinoma, underwent postcontrast T1-weighted SE and GRE MR studies. Detectability of dural sinus invasion and extension was evaluated using two sequences by two neuroradiologists in a blinded manner and compared with surgical results. Quantitative analysis was also performed to calculate the contrast-to-noise ratio (CNR) between lesion and dural sinus on SE and GRE images. The data were analyzed statistically using a matched paired t-test. In the qualitative evaluation, the detectability of dural sinus invasion in 3DFT-GRE images was superior to that using SE images. The mean CNR for all lesions was 3.86 on SE images and 5.63 on 3DFT-GRE images (p = 0.03). For evaluation of dural sinus invasion and the extension of extra-axial tumors, postcontrast 3DFT-GRE MR images were superior to conventional SE images.

Magnetic Resonance Angiography

Magnetic Resonance Angiography

MRI findings in 32 consecutive lipomas using conventional and advanced sequences.

Intracranial lipomas are histologically benign and usually incidental magnetic resonance imaging findings that must be differentiated from ominous lesions. The authors describe 32 lipomas in 30 patients using conventional spin-echo (CSE) T1-weighted images (T1WI), CSE proton density (PDWI), CSE T2-weighted images (T2WI), fast spin-echo (FSE) T2WI, and FSE fluid-attenuated inversion recovery (FLAIR). Lipomas occurred most commonly in the trigonal choroid plexus, cerebral convexity, pericallosal, and quadrigeminal cistern regions. Lipomas were hyperintense on CSE T1WI and of variable appearance on CSE PDWI and CSE T2WI. Lipomas were isointense to hyperintense on FSE T2WI and hyperintense on FLAIR. Chemical shift artifact (CSA) usually was present on either CSE PDWI or CSE T2WI but was not seen on FSE images. One patient had intracranial hypotension associated with a large convexity lipoma. The authors conclude that lipomas appear different on CSE T2WI than on FSE T2WI. CSE PDWI and CSE T2WI are complementary in detecting CSA. The lack of CSA being detected in lipomas on FSE images most likely relates to inherent bandwidth differences compared with those of CSE. The hyperintense appearance of lipomas on FSE FLAIR and FSE T2WI may be confused with subacute hematomas. The authors recommend that if CSE technique by itself is used to exclude lipomas (in centers that are not using FSE), then T1WI, PDWI, and T2WI usually are sufficient. For centers using FSE routinely, fat saturation or CSE sequences also may be needed to exclude lipomas. Finally, the authors' series suggests that intracranial lipomas may occur in lateral locations more frequently than reported previously.

MR imaging of congenital anomalies of the thoracic veins.

Congenital anomalies of the thoracic veins are infrequent but important developmental abnormalities. Thoracic venous anomalies can be classified as systemic or pulmonary. Systemic venous anomalies are often incidental findings, whereas pulmonary venous anomalies are more likely to manifest with cyanosis and to be associated with congenital cardiac abnormalities, especially atrial septal defect. Magnetic resonance (MR) imaging provides excellent delineation of the abnormal vessels and associated cardiac defects. Conventional spin-echo (SE) techniques show blood flow as a signal void and are sufficient for demonstrating the aberrant venous anatomy in most cases. Gradient-echo images show flowing blood as high signal intensity and are useful for clarifying the course of anomalous veins when vessel walls are difficult to visualize on SE images. Phase-contrast images are valuable for ascertaining the direction of blood flow and thus provide a physiologic method of distinguishing the vertical vein of anomalous pulmonary venous return from a left superior vena cava. MR imaging is useful for delineating both the thoracic venous and accompanying intracardiac anomalies and is a valuable, complementary technique to echocardiography, angiography, and computed tomography in the evaluation of patients with these abnormalities.

A practical approach to MRI of coronary artery bypass graft patency and flow.

Direct visualization of coronary artery bypass grafts can be obtained non-invasively by magnetic resonance imaging. Several studies demonstrated a high sensitivity and somewhat lower specificity for detection of vein-graft patency, using the conventional spin-echo and gradient-echo techniques. In addition, the true functional status can be assessed by determining the flowrate within the graft using phase velocity mapping. Important limitations of the previously applied techniques include the inability to accurately evaluate the different segments of jump grafts and the presence of graft stenoses. Further improvement is to be expected from the recent introduction of breath-hold imaging sequences and the forthcoming introduction of bloodpool-avid contrast agents.