MRI: use of the inversion recovery pulse sequence.
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Brain Diseases↗
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Optimization of MRI pulse sequences to visualize the normal pars interarticularis.
Magnetic resonance imaging (MRI) is a potentially useful means of detecting acute pars stress fractures. However, recent publications have highlighted the deficiencies of routine MRI in evaluating the pars interarticularis. Twenty-nine volunteers underwent thin section, multi-planar MR examinations of the lumbar spine to evaluate whether the normal pars could be more reliably demonstrated. MRI examinations were performed with sagittal and reserve angle oblique axial T1W images, and also 3D sagittal gradient echo images with reverse angle reconstructions. Sagittal STIR images were also acquired in 14 cases. Two hundred and ninety pars were evaluated, of which 66% were deemed definitely intact (type I) on the sagittal T1W images alone (continuous marrow throughout the pars). However 93% were deemed intact when all images were reviewed together. The majority of pars defects occur at L4/L5, and 74% of these were intact on the sagittal T1W sequence alone, and 90% on combined sequences. Eighteen pars (6%) were considered to be hypointense (type II) after review of all sequences, but appeared otherwise intact. One volunteer had bilateral definite pars defects (type IV) at L5 on all sequences. This study indicates that improved visualization of the normal pars interarticularis can be achieved with optimized MRI.
Adolescent↗
Comparison of MRI pulse sequences in defining prostate volume after permanent implantation: in regard to McLaughlin et al., IJROBP 2002;54:703-711.
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Brachytherapy↗
Velocity measurement of clay intrusion through a sudden contraction step using a tagging pulse sequence.
Magnetic resonance imaging (MRI) with a spatial tagging sequence was used to measure the velocity distribution of clay that was forced past a sudden contraction. A spatial tagging sequence provided magnetic resonance images of clay that allowed measurement of the velocity distribution in the clay, which can provide profound insights on the deformation process of clay during the intrusion process. The experiments were conducted using a specially-designed vessel that could operate at up to 30 MPa. The vessel offers a rectangle test section with a sudden contraction step that had a ratio of contraction of 2:1. The vessel was installed into a commercial magnetic resonance imaging equipment and then the fluid motion of clay flowing into the narrow contracted channel was quantitatively investigated to examine behaviors of flowing clay as non-Newtonian fluid. MRI results are compared with those obtained by computational fluid dynamics (CFD) calculation. Velocity distributions obtained from each tag displacement did not well agree with those predicted by CFD results near the contraction step where the fluid accelerated rapidly. However, a post-processing on calculation results, in which virtual tag displacement is calculated, gave better agreement with experiment and enabled us to compare MRI results with CFD results.
Aluminum Silicates↗
Relationship between pulse sequences and signal intensity of joint fluid in the gradient-echo MR imaging.
To depict the labrum and meniscus in terms of contrast to joint fluid by increasing its signal intensity, we examined in vitro and in a human subject the good imaging conditions of gradient-echo magnet resonance by using a 1.0 Tesla superconducting imager (Shimadzu). In our in vitro study, 3 types of joint fluid and physiological saline were imaged together with PVA gel (as the substitute for surrounding soft tissue), by using either the STAGE, SSFP, or STERF method, and with several TR's (repetition time); and mean signal intensity was obtained. In order to confirm the findings of the in vitro study, a human study was conducted: physiological saline was injected into a shoulder joint, and axial planes were depicted under the conditions equivalent to those of the in vitro study. With the STERF method, signal intensity of the fluid was high at any flip angle, but PVS gel and the surrounding soft tissues such as muscles were rarely depicted. With the STAGE and SSFP methods, depiction of the fluid, PVA gel, and the surrounding soft tissues were possible by setting an appropriate flip angle for TR: With the STAGE method (a spoiled gradient echo sequence), good imaging was possible by selecting small flip angle, regardless TR. Therefore, because of easiness in selecting conditions, the STAGE method is considered to be the best for diagnostic scanning.
Humans↗
Quantification of gadolinium-DTPA concentrations for different inversion times using an IR-turbo flash pulse sequence: a study on optimizing multislice perfusion imaging.
The purpose of this study was to optimize an inversion-recovery (IR) turbo fast low-angle shot (FLASH) for multislice imaging by evaluating the accuracy of calculated the relaxation-rate (R1) for different inversion times (TI). This is important for tracer kinetic modeling because it requires a system responding linearly to input. R1 are linearly related to changes in the concentration of gadolinium (Gd)-diethylenetriaminepentaacetic acid (DTPA), and R1 is a parameter that can be derived from the magnetic resonance (MR) signal. The accuracy of calculated R1 using an IR turbo fast low-angle shot was evaluated in phantoms and for increasing TIs using spectroscopically measured R1 values as reference. Signal curves, obtained in vivo after a bolus injection of Gd-DTPA, were used in an analytical computer program to study the effect of different TI-values on accurate calculation of R1. Results show that TIeff should be <200 ms to measure the bolus-passage of Gd-DTPA in blood accurately, whereas the myocardial response can be measured correctly for TIeff < 870 ms at 1.5 T. The initial slope of the myocardial signal enhancement curve becomes steeper for larger TI values, whereas the calculated R1 curves were similar, indicating that these curves, rather than signal curves, are more suitable even for qualitative perfusion evaluation. It is concluded that the results can be incorporated in a multislice IR turbo fast low-angle shot using the first slice (with a short TI) for assessment of both the arterial input function and the tissue response and the second slice in another position for assessment of the tissue response alone.
Contrast Media↗
Pulse sequences for detection of NH2...N hydrogen bonds in sheared G . A mismatches via remote, non-exchangeable protons.
The non-detectability of NH...N hydrogen bonds in nucleic acids due to exchange broadened imino/amino protons has recently been addressed via the use of non-exchangeable protons for detecting internucleotide 2hJ(NN) couplings. In these applications, the appropriate non-exchangeable proton is separated by two bonds from the NH...N bond. In this paper, we extend the scope of this approach to protons which are separated by four bonds from the NH...N moiety. Specifically, we consider the case of the commonly occurring sheared G x A mismatch alignment, in which we use the adenine H2 proton to report on the (A)N6H6(1.2)...N3(G) hydrogen bond, in the presence of undetectable, exchange broadened N6H6(1.2) protons. Two sequences, the 'straight-through' (H6)N6N3H2 and 'out-and-back' H2N6N3 experiments, are presented for observing these correlations in H2O and D2O solution, respectively. The sequences are demonstrated on two uniformly 15N,13C labelled DNA samples: d(G1G2G3T4T5C6A7G8G9)2, containing a G3 x (C6-A7) triad involving a sheared G3 x A7 mismatch, and d(G1G2G3C4A5G6G7T8)4, containing an A5 x (G3 x G6 x G3 x G6) x A5 hexad involving a sheared G3 x A5 mismatch.
Base Pair Mismatch↗
Assigning carbon-13 NMR spectra to crystal structures by the INADEQUATE pulse sequence and first principles computation: a case study of two forms of testosterone.
A (13)C CPMAS NMR experiment at high field (11.7 T) has produced significantly improved dispersion for the alpha form of testosterone, allowing revisions and extensions to be made to the assignments. Correlations shown by an INADEQUATE two-dimensional spectrum, recorded at 16.5 T, have allowed the components of most of the doublet signals to be grouped into two sets (for the two crystallographically independent molecules). First-principles computations, employing a fully solid-state approach, have been used to obtain values for the crystallographic splittings, which are discussed in relation to the experimental values. This procedure enables assignments to the two groups to be suggested for all but one of the remaining doublet signals. It also allows the two sets of signals to be identified specifically to the two independent molecules in the crystal structure. Computations were also carried out for the beta form of testosterone (a dihydrate). The shift differences between the alpha and beta forms were compared with the experimental data, with encouraging results. Comparisons were also made between computed and experimental shielding anisotropies and asymmetries for three of the carbons of the alpha form. The methodology has a high potential for future applications, though more examples need to be evaluated before general conclusions can be drawn.
Carbon Isotopes↗
[Magnetic resonance imaging of the wrist--comparison of high resolution pulse sequences and different fat signal suppression techniques in cadavers].
PURPOSE: To evaluate high resolution sequences with and without fat-suppression techniques for MR imaging of the wrist. MATERIALS AND METHODS: 10 cadaver wrist specimens were imaged with 12 MR sequences (SE: 400 ms/20 ms, TSE: 3000 ms/119 ms/17 ms, fatsat (FS) TSE: 3000 ms/17 ms and 3000 ms/45 ms, STIR: 2619 ms/29 ms/160 ms, DESS 3D: 43.7 ms/9 ms/35 degrees FS and 25.4 ms/9 ms/35 degrees water excitation (WE), CISS 3D: 12.2 ms/5.9 ms/40 degrees and FLASH-sequences: 53 ms/11 ms/40 degrees FS, 23 ms/11 ms/40 degrees WE and 45 ms/11 ms/30 degrees FS) at 1.5 T. Slice thickness was 3 mm, FOV 80 x 70 mm (pixel size 0.31 x 0.31 mm). Signal intensity was measured by an ROI in bone marrow, fluid, hyaline cartilage, scapholunate (SL) ligament and triangular fibrocartilage and S/N- and C/N-ratios were calculated. Additionally, a visual evaluation was performed. RESULTS: The highest homogeneity and the least artifacts were achieved by the T1-w SE sequence. For the STIR and PD-FS TSE sequence high rankings were found for the detection of free water. The PD FS sequence had high ranking also for visualization of the SL ligament and the triangular fibrocartilage. The best sequence for the assessment of hyaline cartilage was the FLASH-FS sequence. For detailed analysis of bony structures the CISS sequence performed best. CONCLUSION: The isolated use of a PD-FS-TSE sequence enables for evaluation of all clinically relevant structures at the wrist. Dedicated questions for hyaline cartilage are answered best by the use of a FLASH 3D-FS sequence. Selective water excitation reduces acquisition time to 60%, nevertheless FS sequences are still diagnostically superior to WE sequences.
Adipose Tissue↗
[CT and MRI in tumors of the hypopharynx and larynx--comparison of methods with reference to rapid and ultra-fast MR pulse sequences].
A total of 86 patients with malignant tumours of the hypopharynx and larynx were examined with CT and MRI. The most frequent malignant tumours of the larynx namely, the glottic carcinomas, were better detected with CT than with MRI. The other tumours of the larynx, however, were better visualised with MRI. MRI proved superior to CT in the detection and staging of carcinomas of the hypopharynx. Functional MR images (phonation studies, Valsalva's manoeuvre) were attainable using ultrafast sequences, thus enhancing the diagnostic value of MRI. MRI proved superior to CT enabling a better differentiation of recurrent tumours, inflammatory tissue and scar. For this purpose, T1-weighted plain and contrast-enhanced spin-echo images and T2-weighted spin-echo images were necessary in most cases. T2 weighting turbo spin-echo sequences with relatively short acquisition times proved superior to conventional T2 weighting spin-echo sequences; thanks to shorter acquisition times, the motion artifacts could be reduced and the image quality improved.
Carcinoma, Squamous Cell↗
[CT and MRI in tumors of the mouth and oropharynx--comparison of methods with reference to fast and ultra-fast MR pulse sequences].
A total of 488 patients with neoplasms (in 474 cases with malignant tumours) of the oropharynx, floor of the mouth and oral cavity, were examined with MRI and CT. MRI proved superior to CT, on account of its coronal and sagittal slice orientation enabling not only a better demonstration of findings, but also improved tumour detection and staging. The diagnostic value of MRI was further enhanced with additional fast and ultrafast MR sequences rather than spin echo sequences alone, as previously practised.
Adenocarcinoma↗
Magnetic resonance imaging of hyaline cartilage defects at 1.5T and 3.0T: comparison of medium T2-weighted fast spin echo, T1-weighted two-dimensional and three-dimensional gradient echo pulse sequences.
PURPOSE: To evaluate and compare the diagnostic accuracy of appropriate magnetic resonance (MR) sequences in the detection of cartilage lesions at 1.5T and 3.0T. MATERIAL AND METHODS: Twelve chondral defects of varying depths, widths, and locations were created in the retropatellar hyaline cartilage in six sheep cadaver limbs. Axial images employing three fat-suppressed imaging sequences--(1) a T2-weighted fast spin-echo (FSE) sequence, (2) a two-dimensional (2D) and (3) three-dimensional (3D) gradient-echo (GE) sequence at 1.5T and 3.0T using an extremity quadrature coil--were evaluated by three experienced radiologists. Statistical analysis of the results consisted of receiver operating characteristics (ROC) and significant testing using the bivariate chi-square test. In addition, signal-to-noise ratios (SNR) and contrast-to-noise ratios (CNR) were evaluated with significance testing using the Wilcoxon test. RESULTS: The 3D GE sequence compared favorably with other sequences at 3.0T and 1.5T (Az=0.88 at 3.0T and Az=0.85 at 1.5T) missing only one small grade 2 lesion. 2D GE imaging was inferior to 3D imaging at both field strengths (P<0.05) in general. However, compared to 1.5T, lesion detectability was improved at the higher magnetic field of 3.0T (Az=0.81 and 0.73 at 3.0T and 1.5T, respectively). FSE images showed significantly inferior sensitivity and less anatomical detail compared to the GE sequences at both field strengths (Az=0.64 and 0.72 at 3.0T and 1.5T, respectively; P<0.05). However, compared to 1.5T, lesion detectability SNR and CNR values were superior in all sequences tested at 3.0T. CONCLUSION: MRI at 3.0T improves SNR and CNR significantly in the most common sequences for cartilage MRI, resulting in an improvement in chondral lesion detection. GE imaging therefore allows resolution to be increased in an acceptable time manner for patient comfort, and the 3D GE fat-suppressed sequence at 3.0T appears to be best suited for cartilage imaging in a clinical setting.
Animals↗
Magnetic resonance imaging of the temporomandibular joint: preliminary evaluation of partial flip angle three-dimensional volume acquisitions against conventional single and multiecho pulse sequences.
The authors imaged 20 temporomandibular joints (TMJs) in 20 patients with high field surface coil magnetic resonance imaging, to compare the accuracy and the clinical utility of thin section partial flip angle (PFA) three dimensional (3D) volume acquisitions with T1-weighted images (T1WI), spin echo, multiecho, long TR/short and long TE images, PFA gradient recalled acquisition in the steady state (GRASS) images in the diagnosis of internal derangement of the TMJ. Pathological conditions demonstrated on imaging studies included disk derangement, joint effusion, and osteocartilaginous lesions, such as degenerative arthritis, osteoporosis, osteochondritis dissecans and early avascular necrosis of the mandibular condyle.
Humans↗
Interactions of paramagnetic contrast agents and the spin echo pulse sequence.
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Contrast Media↗
Effects of superparamagnetic iron oxide (AMI-25) on liver and spleen imaging using spin-echo and fast spin-echo magnetic resonance pulse sequences.
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Adult↗
Comparative efficiency of different pulse sequences in MR imaging.
This article examines the relative performance of various sequences in terms of a figure of merit. The range of possible options is large but there are also major constraints on possible improvements by manipulating sequences. The performance of inversion recovery and partial saturation techniques is better than is often suggested.
Adult↗
Comparison of in-phase and opposed-phase GRE and conventional SE MR pulse sequences in T1-weighted imaging of liver lesions.
PURPOSE: Our goal was to compare in-phase (IP) and opposed-phase (OP) GRE and conventional SE sequences in T1-weighted (T1-W) imaging of the liver and to evaluate chemical shift GRE imaging in characterizing liver/lesions for fat content. METHOD: IP and OP T1-W GRE with fast low angle shot (FLASH) technique and T1-W SE sequences were compared in 162 patients at 1.0 T. Chemical shift GRE imaging was used to characterize lesions with fat content. Two hundred sixteen lesions were analyzed in three groups of liver: (a) "normal" liver (n = 74 with 110 lesions); (b) cirrhotic liver (n = 76 with 85 lesions); and (c) fatty liver (n = 12 with 21 lesions). Liver/lesion contrast and liver/lesion contrast-to-noise ratio were assessed for lesion detectability. The percentage of signal intensity variation (SIV) between IP and OP images was used to characterize lesions for fat content. RESULTS: The OP GRE sequence had significantly higher contrast for normal and cirrhotic livers (p < 0.001), and the IP GRE sequence had significantly higher contrast and contrast-to-noise ratio for fatty liver (p < 0.001). There were no significant differences between OP, IP, and T1-W SE imaging in cirrhotic cases for contrast-to-noise ratio (p < 0.28). Chemical shift imaging detected fat in 21 lesions (9.7%, mean SIV, 191.1%) (sensitivity and specificity 100% when compared with fine needle aspiration cytology). CONCLUSION: OP GRE sequences could replace conventional SE sequences in T1-W imaging in nonfatty livers, whereas in fatty livers, T1-W SE sequences could be obviated, but both OP and IP sequences are necessary. Chemical shift imaging (OP and IP) can be used to accurately characterize lesions for fat content.
Analysis of Variance↗
Efficacy of contrast medium use for neuroimaging at 3.0 T: utility of IR-FSE compared to other T1-weighted pulse sequences.
As inversion-recovery (IR) technique improves T1 contrast at high field strength, signal enhancement by T1-shortening contrast media may be affected. To clarify the different enhancement properties at 3.0 T, the authors compared T1-weighted sequences. Twelve contrast-enhancing lesions were investigated by spin-echo (SE), inversion recovery fast spin-echo (IR-FSE), two-dimensional gradient-echo (2D GE), and magnetization-prepared three-dimensional gradient-echo (3D GE) sequences and evaluated by comparing signal-intensity enhancements within the lesions. In addition, signal-to-noise-ratios (SNR) and contrast-to-noise-ratios (CNR) were measured. On average, signal enhancement of the lesions amounted to 60% for SE, 57% for IR-FSE, 32% for 2D GE, and 35% for 3D GE images. CNR of gray matter versus white matter was significantly higher for IR SE and GE imaging than for genuine SE and 2D GE acquisitions (Wilcoxon test), while 2D GE imaging alone had an excellent SNR. As IR-FSE images provide an excellent CNR for gray and white matter in the brain and contrast enhancement performs almost similarly well compared with SE imaging, this technique appears to be well suited for T1-weighted neuroimaging without and with contrast enhancement at 3.0 T. However, the inherent blurring of the IR-FSE can lead to poor performance for very small lesions.
Adult↗