Spin-echo Magnetic Resonance Imaging Sequences Research Articles

Comparison between T2 Turbo Inversion Recovery Magnitude and T2 Frequency Selective Fat Saturation Turbo Spin Echo MRI Sequences in Detection of Perianal Fistula

Fat suppression magnetic resonance imaging (MRI) sequences are routinely included in the MRI protocol for patients with perianal fistula to improve the visibility of the abnormal tracts and abscesses against the background of hypo-signal intensity on the image. The objective of this study is to compare the turbo inversion recovery magnitude (TIRM) and frequency selective fat saturation turbo spin echo (FSTSE) MRI sequences in detecting perianal fistulas in terms of time and clarity. The MRI protocol included a coronal T2 turbo inversion recovery magnitude sequence, a T2 fat saturation turbo spin echo, and T2 turbo inversion recovery magnitude sequences in the axial plane. The evaluation of sequence image quality involved calculating the signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR). Additionally three radiologists assessed the best image using a questionnaire designed to align with the study’s objectives. The T2 TIRM sequence was found to have the highest number of ticked images. The inter-rater kappa agreement showed fair agreement (k = 0.370) between the raters. However, the SNR and CNR values for the T2 FSTSE were higher than those of the T2 TIRM sequence, with a p-value less than 0.001. There is a significant difference in the meantime in that the T2 TIRM sequence has less time than the T2 FSTSE with a p-value < 0.001. Due to its uniform fat suppression in the MR image and shorter acquisition time, the turbo inversion recovery magnitude sequence exhibited superior performance compared to the T2 frequency-selective turbo spin echo sequence.

Lung Nodule Detection With Modern Low-Field MRI (0.55 T) in Comparison to CT.

The aim of this study was to evaluate the accuracy of modern low-field magnetic resonance imaging (MRI) for lung nodule detection and to correlate nodule size measurement with computed tomography (CT) as reference. Between November 2020 and July 2021, a prospective clinical trial using low-field MRI at 0.55 T was performed in patients with known pulmonary nodules from a single academic medical center. Every patient underwent MRI and CT imaging on the same day. The primary aim was to evaluate the detection accuracy of pulmonary nodules using MRI with transversal periodically rotated overlapping parallel lines with enhanced reconstruction in combination with coronal half-Fourier acquired single-shot turbo spin-echo MRI sequences. The secondary outcome was the correlation of the mean lung nodule diameter with CT as reference according to the Lung Imaging Reporting and Data System. Nonparametric Mann-Whitney U test, Spearman rank correlation coefficient, and Bland-Altman analysis were applied to analyze the results. A total of 46 participants (mean age ± SD, 66 ± 11 years; 26 women) were included. In a blinded analysis of 964 lung nodules, the detection accuracy was 100% for those ≥6 mm (126/126), 80% (159/200) for those ≥4-<6 mm, and 23% (147/638) for those <4 mm in MRI compared with reference CT. Spearman correlation coefficient of MRI and CT size measurement was r = 0.87 ( P < 0.001), and the mean difference was 0.16 ± 0.9 mm. Modern low-field MRI shows excellent accuracy in lesion detection for lung nodules ≥6 mm and a very strong correlation with CT imaging for size measurement, but could not compete with CT in the detection of small nodules.

Forensic age estimation via magnetic resonance imaging of knee in the Turkish population: use of T1-TSE sequence

The evaluation of epiphyseal areas by magnetic resonance imaging (MRI) for forensic age estimation is an important supportive diagnostic method to prevent repeated radiation exposure without a valid medical reason. There are still not enough individuals being analyzed with MRI for age estimation. The aim of this study was to investigate the utility of T1-weighted turbo spin echo (T1-TSE) MRI sequences in determining the degree of ossification of the distal femoral and proximal tibial epiphyses in a Turkish population. In this study, images from 649 patients (335 males and 314 females) aged 10–30 years were retrospectively evaluated with sagittal T1-weighted turbo spin echo (T1-TSE) MRI sequences of the knee. Proximal tibial and distal femoral epiphysis were scored by two different observers twice using the combined staging system described by Schmeling and Kellinghaus. Spearman’s rank correlation analysis indicated a significant positive relationship between age and ossification stages of the distal femoral and proximal tibial epiphyses (p < 0.001). The intra- and inter-observer reliabilities in evaluating the femur and tibia were separately determined and gave promising results and Cohen’s kappa statistics ranged from κ = 0.886 and κ = 0.961. The minimal ages of patients with stage 4 ossification were 15.1 years for females and 15.8 years for males for the distal tibial epiphysis and 15.4 years for females and 17 years for males for the distal femoral epiphysis. This study show that (T1-TSE) MRI and the applicability and Schmeling and Kellinghaus staging method of the knee can be performed for living 14- to 17-year-old individuals in need of a supportive noninvasive method for estimating forensic age.

Distortion Correction Protocol for 3T Stereotactic Magnetic Resonance Imaging: A Clinical Study

With application of 3T magnetic resonance imaging (MRI) to functional neurosurgery procedures and given the inherent requirement of millimetric precision, the need to develop a method for correction of geometric image distortion emerged. The aim of this study was to demonstrate clinical safety and practical viability of a correction protocol in patients scheduled to undergo stereotactic procedures using 3T MRI. This prospective study comprised 20 patients scheduled to undergo computed tomography (CT) stereotactic functional procedures or encephalic brain lesion biopsies. The CT images were references for MRI geometric accuracy calculations. For each scan, 2 images were obtained: normal and reversed images. Eight distinct points on CT and MRI were selected summing 152 points that were based on a power analysis calculation value >0.999. One patient was excluded because of the inability to find reliable common landmark points on CT and MRI. The distortion range was 0-5.6 mm and increased proportionally with stereotactic isocenter distance, meaning the distortion was greater in the periphery. After correction, the minimum and maximum distortion found was 0 mm and 3.5 mm, respectively. There was no significant difference between CT and MRI corrected x-coordinates (P > 0.05). The proposed method can satisfactorily correct geometric distortions in clinical 3T MRI studies. Clinical use of the technique can be practical and efficient after software automation of the process. The method can be applied to all spin-echo MRI sequences.

High resolution hemodynamic profiling of murine arteriovenous fistula using magnetic resonance imaging and computational fluid dynamics

BackgroundArteriovenous fistula (AVF) maturation failure remains a major cause of morbidity and mortality in hemodialysis patients. The two major etiologies of AVF maturation failure are early neointimal hyperplasia development and persistent inadequate outward remodeling. Although hemodynamic changes following AVF creation may impact AVF remodeling and contribute to neointimal hyperplasia development and impaired outward remodeling, detailed AVF hemodynamics are not yet fully known. Since murine AVF models are valuable tools for investigating the pathophysiology of AVF maturation failure, there is a need for a new approach that allows the hemodynamic characterization of murine AVF at high resolutions.MethodsThis methods paper presents a magnetic resonance imaging (MRI)-based computational fluid dynamic (CFD) method that we developed to rigorously quantify the evolving hemodynamic environment in murine AVF. The lumen geometry of the entire murine AVF was reconstructed from high resolution, non-contrast 2D T2-weighted fast spin echo MRI sequence, and the flow rates of the AVF inflow and outflow were extracted from a gradient echo velocity mapping sequence. Using these MRI-obtained lumen geometry and inflow information, CFD modeling was performed and used to calculate blood flow velocity and hemodynamic factors at high resolutions (on the order of 0.5 μm spatially and 0.1 ms temporally) throughout the entire AVF lumen. We investigated both the wall properties (including wall shear stress (WSS), wall shear stress spatial gradient, and oscillatory shear index (OSI)) and the volumetric properties (including vorticity, helicity, and Q-criterion).ResultsOur results demonstrate increases in AVF flow velocity, WSS, spatial WSS gradient, and OSI within 3 weeks post-AVF creation when compared to pre-surgery. We also observed post-operative increases in flow disturbances and vortices, as indicated by increased vorticity, helicity, and Q-criterion.ConclusionsThis novel protocol will enable us to undertake future mechanistic studies to delineate the relationship between hemodynamics and AVF development and characterize biological mechanisms that regulate local hemodynamic factors in transgenic murine AVF models.

Sex- and age-dependence of region- and layer-specific knee cartilage composition (spin–spin–relaxation time) in healthy reference subjects

Compositional measures of articular cartilage are accessible in vivo by magnetic resonance imaging (MRI) based relaxometry and cartilage spin-spin transverse relaxation time (T2) has been related to tissue hydration, collagen content and orientation, and mechanical (functional) properties of articular cartilage. The objective of the current study was therefore to evaluate subregional variation, and sex- and age-differences, in laminar (deep and superficial) femorotibial cartilage T2 relaxation time in healthy adults. To this end, we studied the right knees of 92 healthy subjects from the Osteoarthritis Initiative reference cohort (55 women, 37 men; age range 45-78 years; BMI 24.4±3.1) without knee pain, radiographic signs, or risk factors of knee osteoarthritis in either knee. T2 of the deep and superficial femorotibial cartilages was determined in 16 femorotibial subregions, using a multi-echo spin-echo (MESE) MRI sequence. Significant subregional variation in femorotibial cartilage T2 was observed for the superficial and for the deep (both p<0.001) cartilage layer (Friedman test). Yet, layer- and region-specific femorotibial T2 did not differ between men and women, or between healthy adults below and above the median age (54 years). In conclusion, this first study to report subregional (layer-specific) compositional variation of femorotibial cartilage T2 in healthy adults identifies significant differences in both superficial and deep cartilage T2 between femorotibial subregions. However, no relevant sex- or age-dependence of cartilage T2 was observed between age 45-78 years. The findings suggest that a common, non-sex-specific set of layer-and region-specific T2 reference values can be used to identify compositional pathology in joint disease for this age group.

Magnetic Resonance Imaging in Patients With Mechanical Low Back Pain Using a Novel Rapid-Acquisition Three-Dimensional SPACE Sequence at 1.5-T: A Pilot Study Comparing Lumbar Stenosis Assessment With Routine Two-Dimensional Magnetic Resonance Sequences

To minimize the burden of overutilisation of lumbar spine magnetic resonance imaging (MRI) on a resource-constrained public healthcare system, it may be helpful to image some patients with mechanical low-back pain (LBP) using a simplified rapid MRI screening protocol at 1.5-T. A rapid-acquisition 3-dimensional (3D) SPACE (Sampling Perfection with Application-optimized Contrasts using different flip angle Evolution) sequence can demonstrate common etiologies of LBP. We compared lumbar spinal canal stenosis (LSCS) and neural foraminal stenosis (LNFS) assessment on 3D SPACE against conventional 2-dimensional (2D) MRI. We prospectively performed 3D SPACE and 2D spin-echo MRI sequences (axial or sagittal T1-weighted or T2-weighted) at 1.5-T in 20 patients. Two blinded readers assessed levels L3-4, L4-5 and L5-S1 using: 1) morphologic grading systems, 2) global impression on the presence or absence of clinically significant stenosis (n=60 disc levels for LSCS, n=120 foramina for LNFS). Reliability statistics were calculated. Acquisition time was ∼5minutes for SPACE and ∼20minutes for 2D MRI sequences. Interobserver agreement of LSCS was substantial to near perfect on both sequences (morphologic grading: kappa [k]=0.71 SPACE, k=0.69 T2-weighted; global impression: k=0.85 SPACE, k=0.78 T2-weighted). LNFS assessment had superior interobserver reliability using SPACE than T1-weighted (k=0.54 vs 0.37). Intersequence agreement of findings between SPACE and 2D MRI was substantial to near perfect by global impression (LSCS: k=0.78 Reader 1, k=0.85 Reader 2; LNFS: k=0.63 Reader 1, k=0.66 Reader 2). 3D SPACE was acquired in one-quarter the time as the conventional 2D MRI protocol, had excellent agreement with 2D MRI for stenosis assessment, and had interobserver reliability superior to 2D MRI. These results justify future work to explore the role of 3D SPACE in a rapid MRI screening protocol at 1.5-T for mechanical LBP.

Cartilage T1ρ and T2 Relaxation Times in Patients With Mild-to-Moderate Radiographic Hip Osteoarthritis.

To analyze region-specific T1ρ and T2 relaxation times of the hip joint cartilage in relation to presence or absence of radiographic hip osteoarthritis (OA) and presence or absence of magnetic resonance imaging (MRI)-detected cartilage defects. Weight-bearing radiographs and 3T MRI studies of the hip were obtained from 84 volunteers. Based on Kellgren/Lawrence (K/L) scoring of the radiographs, 54 subjects were classified as healthy controls (K/L grade ≤1) and 30 were classified as having mild or moderate radiographic hip OA (K/L grades 2 or 3, respectively). Two-dimensional fat-suppressed fast spin-echo MRI sequences were used for semiquantitative clinical scoring of cartilage defects, and a T1ρ/T2 sequence was used to quantitatively assess the cartilage matrix. The femoral and acetabular cartilage was then segmented into 8 regions and the mean T1ρ/T2 values were calculated. Differences in T1ρ and T2 relaxation times were compared between subjects with and those without radiographic hip OA, and those with and those without femoral or acetabular cartilage defects. Higher T1ρ and T2 relaxation times in the anterior superior and central regions of the acetabular cartilage were seen in individuals with radiographic hip OA and those with acetabular cartilage defects compared to their respective controls (P < 0.05). In the femoral cartilage, the differences in T1ρ and T2 were not significant for any of the comparisons. Significant differences in the T1ρ and T2 values (each P < 0.05) were found in more subregions of the cartilage and across the whole cartilage when subjects were stratified based on the presence of MRI-detected cartilage defects than when they were stratified based on the presence of radiographic hip OA. T1ρ and T2 relaxation parameters are sensitive to the presence of cartilage degeneration. Both parameters may therefore support MRI evidence of cartilage defects of the hip.

Correlation between brain volume change and T2 relaxation time induced by dehydration and rehydration: implications for monitoring atrophy in clinical studies.

Brain volume change measured from magnetic resonance imaging (MRI) provides a widely used and useful in vivo measure of irreversible tissue loss. These measurements, however, can be influenced by reversible factors such as shifts in brain water content. Given the strong effect of water on T2 relaxation, we investigated whether an estimate of T2 relaxation time would correlate with brain volume changes induced by physiologically manipulating hydration status. We used a clinically feasible estimate of T2 (“pseudo-T2”) computed from a dual turbo spin-echo MRI sequence and correlated pseudo-T2 changes to percent brain volume changes in 12 healthy subjects after dehydration overnight (16-hour thirsting) and rehydration (drinking 1.5 L of water).We found that the brain volume significantly increased between the dehydrated and rehydrated states (mean brain volume change = 0.36%, p = 0.0001) but did not change significantly during the dehydration interval (mean brain volume change = 0.04%, p = 0.57). The changes in brain volume and pseudo-T2 significantly correlated with each other, with marginal and conditional correlations (R2) of 0.44 and 0.65, respectively.Our results show that pseudo-T2 may be used in conjunction with the measures of brain volume to distinguish reversible water fluctuations and irreversible brain tissue loss (atrophy) and to investigate disease mechanisms related to neuro-inflammation, e.g., in multiple sclerosis, where edema-related water fluctuations may occur with disease activity and anti-inflammatory treatment.

Abstract 18: The Effect of Lipid Modification on Peripheral Arterial Disease after Endovascular Intervention Trial (ELIMIT)

BACKGROUND The Effect of Lipid Modification on Peripheral Arterial Disease after Endovascular Intervention Trial (ELIMIT), a prospective double-blind randomized study, was designed to determine over 24-months, the effects of triple drug lipid modification therapy versus mono therapy on the progression of atherosclerotic lesions in the distal superficial femoral artery (SFA), as assessed by 3.0T magnetic resonance imaging (MRI). METHODS A total of 95 patients were randomized to either mono therapy with simvastatin (40mg) or triple therapy with simvastatin (40mg), extended-release niacin (1.5g), and ezetimibe (10mg). MR imaging was performed at baseline, 6-, 12-, and 24-months. SFA wall, lumen, and total vessel volumes were quantified using inter-visit co-registered proton-density-weighted turbo spin echo MRI sequences. MRI derived SFA parameters and lipids were analyzed with multi-level models and non-parametric tests, respectively. RESULTS Baseline characteristics did not differ between mono and triple therapy groups, except for ethnicity (Table). There was no difference in adverse cardiovascular events between groups (p=0.99). SFA wall, lumen, and vessel volumes increased non-significantly for both groups between baseline and 24-months. Non-high-density lipoprotein cholesterol showed a larger reduction in triple therapy compared with mono therapy at 12-months (p=0.01). CONCLUSION Despite improved atherogenic lipid profiles, there was no significant difference between mono therapy with simvastatin and triple therapy with simvastatin, extended-release niacin, and ezetimibe for the 24-month changes in total SFA wall, lumen, and vessel volumes.

Isotropic three‐dimensional MRI‐Fricke‐infused gel dosimetry

Fricke-infused gel has been shown to be a simple and attainable method for the conformal measurement of absorbed radiation dose. Nevertheless, its accuracy is seriously hindered by the irreversible ferric ion diffusion during magnetic resonance imaging, particularly when three-dimensional (3D) dose measurement in radiosurgery is considered. In this study, the authors developed a fast three-dimensional spin-echo based Fricke gel dosimetry technique to reduce the adverse effects of ferric ion diffusion and to obtain an accurate isotropic 3D dose measurement. A skull shaped phantom containing Fricke-infused gel was irradiated using Leksell Gamma Knife. The rapid image-based dosimetry technique was applied with the use of a 3D fast spin-echo magnetic resonance imaging sequence. The authors mathematically derived and experimentally validated the correlations between dose-response characteristics and parameters of the 3D fast spin-echo MR imaging sequence. Absorbed dose profiles were assessed and compared to the calculated profiles given by the Gamma Knife treatment planning system. Coefficient of variance (CV%) and coefficient of determination (R(2)) were used to evaluate the precision of dose-response curve estimation. The agreement between the measured and the planned 3D dose distributions was quantified by gamma-index analysis of two acceptance criteria. Proper magnetic resonance imaging parameters were explored to render an accurate three-dimensional absorbed dose mapping with a 1 mm(3) isotropic image resolution. The efficacy of the dose-response estimation was approved by an R(2) > 0.99 and an average CV% of 1.6%. Average gamma pass-rate between the experimentally measured and GammaPlan calculated dose distributions were 83.8% and 99.7% for 2%/2 and 3%/3 mm criteria, respectively. With the designed MR imaging sequence and parameters, total 3D MR acquisition time was confined to within 20 min postirradiation, during which time ferric ion diffusion effects were negligible, thus enabling an accurate 3D radiation dose measurement.

Respiratory Amplitude Guided 4-Dimensional Magnetic Resonance Imaging

To evaluate the feasibility of prospectively guiding 4-dimensional (4D) magnetic resonance imaging (MRI) image acquisition using triggers at preselected respiratory amplitudes to achieve T(2) weighting for abdominal motion tracking. A respiratory amplitude-based triggering system was developed and integrated into a commercial turbo spin echo MRI sequence. Initial feasibility tests were performed on healthy human study participants. Four respiratory states, the middle and the end of inhalation and exhalation, were used to trigger 4D MRI image acquisition of the liver. To achieve T(2) weighting, the echo time and repetition time were set to 75 milliseconds and 4108 milliseconds, respectively. Single-shot acquisition, together with parallel imaging and partial k-space imaging techniques, was used to improve image acquisition efficiency. 4D MRI image sets composed of axial or sagittal slices were acquired. Respiratory data measured and logged by the MRI scanner showed that the triggers occurred at the appropriate respiratory levels. Liver motion could be easily observed on both 4D MRI image datasets by sensing either the change of liver in size and shape (axial) or diaphragm motion (sagittal). Both 4D MRI image datasets were T(2)-weighted as expected. This study demonstrated the feasibility of achieving T(2)-weighted 4D MRI images using amplitude-based respiratory triggers. With the aid of the respiratory amplitude-based triggering system, the proposed method is compatible with most MRI sequences and therefore has the potential to improve tumor-tissue contrast in abdominal tumor motion imaging.

Protocol for MRI of the Hips After Spica Cast Placement

In reduction of hip displacement in developmental dysplasia, concentric placement of the femoral head within the acetabulum is key. Magnetic resonance imaging (MRI) is an effective modality to assess the adequacy of the reduction, but sedation may be required due to the length of the examination. MRI is also more expensive than other imaging modalities. Our goal was to provide an MRI protocol that does not require sedation and can be performed in <15 minutes. We retrospectively reviewed 34 consecutive MRI studies performed without sedation after spica cast placement in 24 developmental hip dysplasia patients. The MRI examinations were performed with a variety of techniques. Sequences used were evaluated for contrast, resolution, and motion artifact. Ninety-seven percent of studies were diagnostic, although 18% of examinations had significant motion artifact. Seven sequences were analyzed. T2-weighted fast spin echo sequences had the best overall scores and were performed in <3 minutes. T1 and fat-suppressed T2-weighted fast spin echo sequences did not score as well, and also required <3 minutes. Single-shot fast spin echo sequences scored poorly due to decreased contrast and resolution, despite shorter acquisition times of 20 to 40 seconds. Three-dimensional (3D) gradient recovery imaging scored poorly due to lower contrast and increased motion due to longer acquisition times of approximately 4 minutes. Both coronally and axially oriented sequences satisfactorily assessed femoral head position within the acetabulum. MRI is a useful tool in evaluating the hips without radiation exposure and without sedation in infants and toddlers after spica cast placement. Both axial and coronal T2 fast spin echo MRI sequences provided excellent anatomic definition and required ≤3 minutes per sequence. Orthopaedic surgeons can request these 2 sequences for accurate assessment of concentric reduction with a potential study time of 15 minutes, obviating the need for sedation. Level II.

Anatomical and Functional Assessment of Brown Adipose Tissue by Magnetic Resonance Imaging

Brown adipose tissue (BAT) is the primary tissue responsible for nonshivering thermogenesis in mammals. The amount of BAT and its level of activation help regulate the utilization of excessive calories for thermogenesis as opposed to storage in white adipose tissue (WAT) which would lead to weight gain. Over the past several years, BAT activity in vivo has been primarily assessed by positron emission tomography-computed tomography (PET-CT) scan using 2-[18F]-fluoro-2-deoxy-D-glucose (18F-FDG) to measure glucose utilization associated with BAT mitochondrial respiration. In this study, we demonstrate the feasibility of mapping and estimating BAT volume and metabolic function in vivo in rats at a 9.4T magnetic resonance imaging (MRI) scanner using sequences available from clinical MR scanners. Based on the morphological characteristics of BAT, we measured the volume distribution of BAT with MRI sequences that have strong fat-water contrast. We also investigated BAT volume by utilizing spin-echo MRI sequences. The in vivo MRI-estimated BAT volumes were correlated with direct measurement of BAT mass from dissected samples. Using MRI, we also were able to map hemodynamic responses to changes in BAT metabolism induced pharmacologically by β3-adrenergic receptor agonist, CL-316,243 and compare this to BAT activity in response to CL-316,243 assessed by PET 18F-FDG. In conclusion, we demonstrate the feasibility of measuring BAT volume and function in vivo using routine MRI sequences. The MRI measurement of BAT volume is consistent with quantitative measurement of the tissue ex vivo.

Evaluation of the contrast between tissues and thermal lesions in rabbit in vivo produced by high intensity focused ultrasound using fast spin echo MRI sequences

In this paper the goal was to measure the contrast to noise ratio (CNR) of fast spin echo (FSE) magnetic resonance imaging (MRI) sequences in detecting thermal lesions created by high intensity focused ul-trasound (HIFU) in rabbit kidney, liver, heart, and brain and lamb pancreas. A spherically focused transducer was used which is navigated inside MRI by a custom made positioning device. A simple simu-lation model was developed which predicts the CNR for the two FSE MRI sequences. The maximum con-trast measured with T1-W FSE ranges from 10 to 25. For all 5 tissues of interest if one uses TR between 400 and 500 ms the contrast is maximized. The T1 and T2 value of lesion depends strongly on the host tissue and is always lower than the host tissue. The greater the difference in T1 value, the greater the CNR. The simulated model for predicting the CNR was proven successful. The CNR measured with T2-W FSE varies between 12 and 15 for all 5 tissues. With T2-W FSE if one uses TE between 40 and 50 ms, the contrast is maximized.

Pulse sequence and timing of contrast‐enhanced MRI for assessing blood–brain barrier disruption after transcranial focused ultrasound in the presence of hemorrhage

To optimize the timing of contrast-enhanced magnetic resonance imaging (MRI) that best indicates blood-brain barrier (BBB) disruption induced by focused ultrasound (FUS) along with an ultrasound contrast agent (UCA) and to verify that the contrast-enhanced spin-echo MRI sequence can indicate the degree and location of BBB disruption in the presence of hemorrhage better than a gradient-echo sequence. Sonication was applied to 12 rat brains with four different doses of UCA to cause variable degrees of hemorrhage. Two imaging sequences were performed to acquire T1-weighted (T1W) images at two time-points after the administration of a T1-shortening contrast agent. The contrast enhancement at the sonicated regions was quantified and correlated against Evans blue (EB) staining. The spin-echo T1W images at 10 minutes post-contrast enhancement showed the best correlation with EB staining in both quantity of EB extravasation (r = 0.812; P < 0.01) and spatial distribution (r = 0.528, P < 0.01). This capability was more robust than the gradient-echo sequence. Our results suggest that contrast-enhanced T1W spin-echo sequence acquired in the early phase post-contrast enhancement should be considered to monitor the degree and location of BBB disruption under the possibility of hemorrhage induced by FUS.

Prevalence, Distribution, and Morphology of Ossification of the Ligamentum Flavum

Large scale, cross-sectional imaging study of a general population. To evaluate the prevalence, morphology, and distribution of ossification of the ligamentum flavum (OLF) in a population, and synthesize the scientific literature on the prevalence of OLF and some factors associated with its occurrence. OLF is a rare disease in which the pathogenesis has not been conclusively established. Little is known about its epidemiology. To date, there is no study that comprehensively assessed the distribution and prevalence of OLF in the whole spine using magnetic resonance imaging (MRI). A total of 1736 southern Chinese volunteers (1068 women; 668 men) between 8 and 88 years of age (mean, 38 years) were recruited by open invitation. MRI was administered to all the participants. T2-weighted, 5-mm spin-echo MRI sequences of the whole spine were obtained. Presence of OLF was identified as an area of low signal intensity in the T2 sagittal sequence located in the posterior part of the spinal canal, and subsequently confirmed by computed tomography scans showing areas of ossification within the ligamentum flavum. The distribution of OLF was classified into 3 types: the isolated type, continuous type, and noncontinuous type. While the morphology of the lesion was classified into triangular, round, and beak shapes based on the pattern of ossification on T2-weighted sagittal MRIs. OLF was identified in a total of 66 subjects or 3.8% of the population (52 women and 14 men). In 45(68.2%) cases, OLF was present at a single-level (isolated type), whereas in 21 (31.8%) cases OLF was present at multiple levels. The isolated type was found in 45 (68.2%) cases, continuous type in 11 (16.7%), and noncontinuous type in 10 (15.2%). The most common site of involvement is the lower thoracic spine, but they can also occur in the upper thoracic spine. The majority of the segments had a round morphology (n = 75: 81.5%), while 17 (18.5%) segments were triangular in shape. A literature review of the past 26 years showed only 4 reports on the prevalence of OLF, all were in special patient groups. Case reports have described postoperative paraplegia from failure to identify and decompress all stenotic segments of OLF. This study demonstrated that OLF is not uncommon, and that some 15% of the lesions are noncontinuous, and therefore could be missed. The authors recommend that for patients undergoing surgical decompression for 1 level of OLF, the whole spine should be routinely screened for other stenotic segments. Failure to do so could result in paraplegia from the nondecompressed levels.

Evaluation of fast spin echo MRI sequence for an MRI guided high intensity focused ultrasound system for in vivo rabbit liver ablation

The effectiveness of magnetic resonance imaging (MRI) to monitor thermal lesions created by High Intensity Focused Ultrasound (HIFU) in rabbit liver in vivo is investigated. The MRI sequences of T1- weighted, and T2-weighted fast spin echo (FSE) were evaluated. The main goal in this paper was to find the range of repetition time (TR) and range of echo time (TE) which maximizes the contrast to noise ratio (CNR). An ultrasonic transducer operating at 2 MHz was used, which is navigated using a positioning device. With T1W FSE the range of TR under which CNR is maximized ranges from 400 to 900 ms. The maximum contrast measured is approximately 25. With T2W FSE the range of TE that establishes maximum contrast is between 40 ms and 80 ms, with CNR of approximately 14. T1W FSE is much better than T2W FSE in detecting thermal lesions in liver. Both T1W and T2 W FSE were proven successful to image thermal lesions created by HIFU in rabbit liver in vivo.

The Appendix in Pregnancy

To estimate the position of the appendix in term pregnancy using magnetic resonance imaging (MRI) technique. Appendiceal distance from the iliac crest and axis rotation were determined in women between 39 and 40 weeks of gestation who were undergoing scheduled repeat cesarean delivery. A single-shot fast spin-echo MRI sequence of the maternal pelvis was performed without gadolinium contrast. A board-certified radiologist interpreted the MRIs and measured the distance from the base of appendix (or cecum) to the iliac crest in centimeters as well as the axis of the appendix using clock position annotation. Seventy-two women had optimal imaging for interpretation. The mean displacement of the appendix above the iliac crest was 45 mm and was significantly higher than previously described in the term pregnant woman (P<.001). Despite recent studies supporting the contrary view, the upward displacement of the appendix in term pregnancy is confirmed in this study. II.

Active MS plaques: efficiency of contrast-enhanced magnetization transfer subtraction technique

T1-weighted (T1W) magnetic resonance images with magnetization transfer (MT) are widely used in the evaluation of multiple sclerosis (MS) plaques. We aimed to evaluate the contribution of the subtraction technique with MT in the detection of acute MS plaques. Sixty-four patients during an MS attack were enrolled in the study. Axial T1W spin echo (SE) with MT, axial-sagittal T2W fast SE, axial FLAIR and postcontrast axial T1W SE magnetic resonance imaging sequence with MT were acquired from all patients. The subtraction (postcontrast-precontrast) images were obtained on the workstation. FLAIR and T2W images were used as reference for plaque imaging. Contrast material enhanced plaques were considered as acute plaques. Qualitatively, both subtracted and contrast-enhanced with MT images were evaluated visually. Quantitatively, signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR) were calculated. A total of 464 plaques were detected on T2W and FLAIR images. Thirty-five acute plaques were detected on both postcontrast MT and subtracted images. Additionally, 66 acute plaques were only detected on subtracted images visually. CNR and SNR values of acute MS plaques were significantly higher on subtracted MT images than on postcontrast MT images (P < 0.001). The subtraction technique seems to facilitate the detection of acute MS plaques by intensifying the visibility of poorly enhanced plaques without use of high dose contrast medium. We suggest the use of subtraction technique in routine imaging work-up of MS patients with acute attacks.