T1-weighted Turbo Fast Low-angle Shot Research Articles

The Direction of Flow and Phase-encoding Schemes Effects on Signal Intensity in T1-weighted Inversion Recovery TurboFLASH Images.

It is needed to minimize the effect of flow direction on the desired area, such as arterial input function (AIF) in magnetic resonance imaging (MRI). The current study aimed to investigate the effect of flow direction on different velocities (0-80.39 cm/s) for the strength of the signal intensity (SI) at the linear phase-encoding (LPE) and the center out phase-encoding (COPE) schemes and to recommend the best flow direction in a selected slice and scheme for absolute perfusion measurement by inversion recovery T1-weighted turbo fast low-angle shot (TurboFLASH) MR images. In this experimental study, the flow rates were measured using a flow phantom, and the signal intensity (SI) was measured at the two opposite flow directions in the Z-axis perpendicular to the coronal image at a concentration of 0.8 mmol/L of gadolinium-diethylenetriaminepantaacetic acid (Gd-DTPA) by using the LPE and COPE schemes. The increase in velocity along with the growth in SI and inflow affected the use of LPE and COPE acquisitions in both directions. The velocity of the arterial input function is needed to calculate the inflow correction factor by using two schemes in two opposite flow directions to investigate perfusion. The COPE scheme was better than the LPE scheme in measuring perfusion since the velocity and direction of blood flow affect SI less.

Initial Evaluation of Non–Contrast-Enhanced Magnetic Resonance Angiography in Patients With Peripheral Arterial Occlusive Disease at 7 T

The aim of this study was to achieve initial experience with non-contrast-enhanced (ne) magnetic resonance angiography (MRA) of the lower leg arteries in patients with peripheral arterial occlusive disease (PAOD) at 7 T. Seven patients with PAOD were examined on a 7-T whole-body magnetic resonance system. A custom-built 16-channel transmit/receive coil and a manually positionable AngioSURF table were used for multistation imaging. For ne-MRA, an axial T1-weighted Turbo-fast low angle shot sequence (repetition time, 700 milliseconds; echo time, 3.84 milliseconds; bandwidth, 930 Hz/pixel; voxel volume, 1 × 1 × 2 mm; matrix, 384 × 288) with phonocardiogram gating was acquired at 7 T. Acquisition time of an entire angiogram covering the vasculature from pelvis to feet amounted to approximately 30 minutes, depending on the patient's heart frequency. All patients underwent a contrast-enhanced MRA (ce-MRA) at 1.5 T as standard of reference. The presence of stenosis and occlusions was evaluated segment based and compared for both MRA techniques. The degree of stenosis was defined as low grade (<50%), high grade (50%-99%), and occlusion (100%). High-grade stenosis and occlusion were considered to be hemodynamically significant stenosis. The 7-T ne-MRA enabled a homogenous, hyperintense artery signal and nearly total venous suppression with accurate delineation of arterial anatomy both proximal and distal to stenotic disease. A total of 154 artery segments were depicted with ce-MRA at 1.5 T. At 7 T, only 124 segments (80.5%) were displayed and involved for analysis, as the iliacal region was displayed incompletely in 4 patients because of the fact that the fixed coil diameter was too small to contain the lower abdomen and pelvis of these patients. In comparison with ce-MRA at 1.5 T as the reference standard, there was total agreement regarding the characterization of an artery segment as being normal or having any kind of stenosis. Of the 124 included segments, 28 segments (23%) had hemodynamically significant stenosis evaluated with 7-T ne-MRA and 26 segments (21%) assessed with 1.5-T ce-MRA. The sensitivity and specificity values of 7-T ne-MRA for detecting segments with hemodynamically significant stenosis were 93% and 98%, respectively. Non-contrast-enhanced MRA by means of T1-weighted Turbo-fast low angle shot imaging at 7 T in patients with PAOD is feasible and allowed for good visualization of stenosis and occlusions in all analyzed artery segments in this small patient group. However, this study also shows the challenges of ultrahigh-field body imaging, and more experience is required to determine the impact of 7-T ne-MRA in clinical practice.

Effect of concentration of contrast agent on the inflow effect for measuring absolute perfusion by use of inversion recovery T1-weighted TurboFLASH images

Previous studies have shown that the organ blood flow (OBF) calculated from the T₁-weighted MRI technique was lower than expected. The inflow correction was one of the main corrections for measuring the absolute OBF. Our aim in this study was to investigate the influence of the contrast agent concentration on inflow effect on signal intensity (SI) and to find the gradient of different flow rates at different concentrations by use of inversion recovery T₁-weighted turbo fast low angle shot (TurboFLASH) MRI images. We performed these studies at six different concentrations of gadolinium-diethylenetriamine-pantaacetic acid (Gd-DTPA) to find the inflow effect on the SI. A flow phantom made of Perspex was designed that produced four different flow rates at the same time. The non-uniformity of the clinical head and neck coil was measured and applied to the SI for measuring the corrected SI. The corrected SI was measured at different flow rates and concentrations. The results indicated that an increase in the flow rate and in the concentration of the contrast agent was associated with an increase in the gradient of the flow rate. The results also indicated that the inflow correction could be ignored when the concentration was low for measurement of the absolute OBF. At high concentrations, the inflow effect should be considered in calculations of the absolute OBF.

Functional MRI in the evaluation of oesophageal motility: feasibility, MRI patterns of normality, and preliminary experience in subjects with motility disorders

The aim of this study was to introduce functional magnetic resonance imaging (fMRI) with T1-weighted turbo fast low-angle shot (FLASH) sequences in the evaluation of oesophageal motility and morphology, to formulate MRI patterns of normality in healthy subjects and to demonstrate the feasibility of the method by obtaining a preliminary experience in the study of subjects affected by oesophageal motility disorders. Thirty healthy volunteers and seven patients with radiological and manometric diagnoses of oesophageal motility disorders underwent fMRI with dynamic T1- weighted turbo-FLASH (TFL) sequences during the administration of oral contrast material. Evaluation of oesophageal function and morphology proved possible in all subjects, as well as the formulation of normality patterns. In patients with motility disorders, fMRI correctly visualised the typical alterations in agreement with radiological and manometric findings. Functional MRI sequences acquired during the administration of oral contrast material can evaluate oesophageal transit, providing information on motility and morphology; furthermore, this modality can properly visualise the typical functional and morphological alterations of motility disorders.

Accuracy of non-enhanced MRI to monitor histological lesion size during laser-induced interstitial thermotherapy

The purpose of this study was to assess the accuracy of non-enhanced MRI using a T1-weighted 2D turbo fast low-angle shot (FLASH) sequence during laser-induced interstitial thermotherapy (LITT) to determine histological lesion size of laser-induced hepatic lesions. The LITT was performed on pig liver samples at various power settings and durations. For MR monitoring during and after LITT a T1-weighted 2D turbo-FLASH sequence was applied. Lesions seen by MRI during and after LITT were correlated with histological lesion size. Histologically, a core zone of complete tissue ablation close to the tip of the applicator could be differentiated from an adjacent transitional zone showing incomplete necrosis. Magnetic resonance imaging right at the end of LITT (i.e., with maximum heating effects) grossly overestimated the core zone but accurately described the transitional zone. Magnetic resonance imaging after cooling of the tissue (therefore showing structural as opposed to thermal changes) exactly depicted the core zone of complete tissue ablation. Non-enhanced MRI using a T1-weighted 2D turbo FLASH sequence strongly overestimates the histological lesion size during LITT; however, structural changes of the tissue seen after cooling accurately define lesion size in LITT. For clinical purposes the lesion geometry seen during MR monitoring should therefore well extend the tumor margins.

Analysis of First-Pass and Delayed Contrast-Enhancement Patterns of Dysfunctional Myocardium on MR Imaging

The purpose of the study was to analyze first-pass and delayed contrast-enhancement patterns of dysfunctional myocardial regions on MR imaging after injection of gadopentetate dimeglumine to predict myocardial viability in patients with coronary artery disease. Twelve patients with wall motion abnormalities and related coronary artery disease revealed by conventional coronary angiography underwent MR imaging at 1.5-T before and 3 months after revascularization therapy. Short-axis images were acquired using a cine gradient-echo sequence. Each slice was divided into eight segments. Overall, 73 segments with impaired contractility were imaged during the first-pass and 14 +/- 2 min after injection of 0.05-mmol/kg gadopentetate dimeglumine at a flow of 3 ml/sec using a T1-weighted turbo fast low-angle shot sequence. Improved systolic wall thickening 3 months after revascularization served as the criterion of viability. At study entry, 26 dysfunctional segments showed delayed hyperenhancement compared with the adjacent functional segments within the same slice, and 47 did not reveal hyperenhancement. After revascularization, 25 (96%) of the 26 hyperenhanced segments did not recover function, whereas 39 (83%) of the 47 segments without hyperenhancement showed mechanical improvement. Segment-related sensitivity and specificity for the correlation of lack of delayed hyperenhancement with myocardial viability were 39 (98%) of 40 and 25 (76%) of 33, respectively. Hypoenhancement during first-pass did not serve as a reliable criterion of viability. Evidence of delayed hyperenhancement of dysfunctional myocardium may be used to predict lack of mechanical improvement or nonviability, whereas the lack of hyperenhancement can be correlated with improvement of regional contractility or viability after revascularization.

Evaluating signal intensity of movement-impaired myocardial segments in MR delayed images after administration of Gd-DTPA. Correlation of regional increase in contraction after revascularization

The aim of the study was to correlate delayed contrast enhancement of dysfunctional regions of the myocardium after injection of Gd-DTPA with the improvement of regional contractility 3 months after revascularization. Eleven patients with coronary artery disease and wall motion abnormalities underwent MR imaging before and 3 months after revascularization therapy (PTCA or CABG). Short-axis images were acquired using a cine gradient echo sequence. After revascularization, a representative slice was analyzed 14 +/- 1 min after injection of 0.1 mmol/kg Gd-DTPA using a T1-weighted turbo fast low-angle shot sequence. Improved systolic wall thickening 3 months after revascularization served as criterion of viability and was correlated with delayed contrast enhancement patterns. After revascularization, 6 patients showed complete recovery of the dysfunctional area, 1 patient partial recovery, and 4 patients remained unchanged. All 4 patients with persisting wall motion abnormalities, 1/6 patients with recovery and the patient with partial recovery revealed a delayed enhancement. Three months after revascularization, delayed enhancement of dysfunctional myocardium is evident in patients without regional wall motion improvement, while the lack of delayed enhancement correlates with improvement of regional contractility.

Does a higher concentration of gadolinium chelates improve first-pass cardiac signal changes?

The purpose of this study was to evaluate first-pass cardiac signal changes with a higher concentrated gadolinium-chelate (gadobutrol) and its influence on bolus geometry. Phantom studies and in vivo first-pass cardiac studies were performed in rabbits (n = 8 experiments) under general anesthesia at 1.0 T using an ultrafast T1-weighted Turbo-fast low-angle shot (FLASH) sequence (TR/TE 4.7/1. 6 msec, alpha = 90 degrees ) with a time resolution of 870 msec. Gadobutrol was injected as an intravenous bolus at two concentrations (0.5 and 1.0 mol Gd/L) and five doses (0.3, 0.15, 0.1, 0.055, and 0.03 mmol Gd/kg bw). The blood-pool gadolinium compound gadopentetate dimeglumine-polylysine (0.15, 0.075, 0.05, and 0.015 mmol Gd/kg bw, 0.5 mol Gd/L) and the standard extracellular gadopentetate dimeglumine (0.1 and 0.05 mmol Gd/kg bw, 0.5 mol Gd/L) served as reference agents. Cardiac signal changes were calculated from serial signal intensity measurements. Maximum signal intensity changes and best peak profiles during first pass of the right and left ventricle were observed with a dose of 0.03 mmol Gd/kg bw gadobutrol using T1-weighted Turbo-FLASH. At the low application volumes used, the higher concentration of 1.0 mol Gd/L gadobutrol did not increase the degree of signal intensity changes or sharpen the bolus profile. First-pass cardiac signal changes using T1-weighted Turbo-FLASH with the new extracellular contrast agent gadobutrol are best observed at a dose of 0.03 mmol Gd/kg bw. There is no advantage to the concentrated formulation (1 mol Gd/L gadobutrol) when using small injection volumes. J. Magn. Reson. Imaging 1999;10:806-812.

MR-monitored LITT as a palliative concept in patients with high grade gliomas: preliminary clinical experience.

The purpose of this study was to evaluate the clinical utility of laser-induced thermotherapy (LITT) as a palliative treatment for patients with high-grade gliomas. Four consenting patients with recurrent high grade III/IV gliomas near the primary language or motor areas were palliatively treated with LITT (2-5 W, 3-13 minutes; Neodym YAG Laser, Dornier, Friedrichshafen, Germany). Temperature monitoring was performed by T1-weighted turbo-fast low-angle shot (FLASH) imaging at 1.5 T (Siemens Magnetom SP 4000, Siemens, Erlangen, Germany). MRI studies before LITT included contrast-enhanced conventional scans and functional activation studies to localize the primary motor cortex or language areas using an echo-planar imaging (EPI) spin-echo (SE) sequence. Follow-up studies consisted of contrast-enhanced conventional scans as well as diffusion studies (contrast-enhanced Fourier-acquired steady-state technique and EPI-SE) and perfusion studies (EPI-SE with .2 mmol of gadolinium (Gd)/kg body weight) to differentiate post-therapeutic effects from residual or recurrent tumor growth. Local tumor control was achieved in areas with laser energy deposition with clinically stable conditions > or = 6 months. Conventional contrast-enhanced scans demonstrated strong enhancement surrounding ablated tumor components, which showed a reduction in CBV/CBF. Perfusion studies were useful to discriminate granulomatous tissue enhancement from residual or recurrent tumor growth. Careful application of LITT may evolve as an alternative palliative concept for patients with end-stage high-grade cerebral gliomas reducing clinical symptoms from circumscribed areas of pathology.