Three-dimensional coronary artery MR imaging using prospective real-time respiratory navigator and linear phase shift processing: comparison with conventional coronary angiography.

Respiratory gating with navigator echo is a recent technique to detect diaphragm position in 3D magnetic resonance (MR) coronary angiography. The purpose of our study was to image proximal coronary arteries and to detect significant stenoses in patients with coronary artery diseases and to compare with contrast enhanced angiography results. Twenty patients with coronary artery diseases who were referred for conventional angiography underwent magnetic resonance angiography (MRA). Three-dimensional gradient echo volumes were acquired using cardiac and respiratory gating and fat suppression. Using reformatted oblique planes and maximum intensity projection technique, visualization coronary segments and detection of significant coronary stenoses were made. Eighty-three coronary segments were analyzed. The sensitivity and specificity were 65% and 93%, respectively. The corresponding positive and negative predictive values were 69% and 91%. This study shows the ability to image correctly coronary arteries and to identify proximal stenoses, but image quality need to be improved for an efficiency detection of coronary artery stenoses in clinical practice.     

Cardiac-synchronized gadolinium-enhanced MR angiography: preliminary experience for the evaluation of the thoracic aorta

Gadolinium (Gd)-enhanced three-dimensional breath-hold magnetic resonance cardiac-synchronized angiography was performed in 13 patients suspected or known to have thoracic aortic disease. High-quality angiograms of the ascending/descending thoracic aorta and coronary arteries were obtained with this method. MR angiograms were compared with Gd-enhanced angiograms obtained without cardiac synchronization. Synchronized imaging showed significantly better aortic valve leaflet and proximal coronary artery depiction. Synchronization reduced motion artifacts, allowing better visualization of the aortic root and proximal coronary arteries.     

Time-resolved and high-resolution MRA in a rabbit model of pulmonary embolism at 7 T: preliminary results

Purpose

Evaluate feasibility of using time-resolved and high-resolution, contrast-enhanced magnetic resonance angiography (MRA) at 7 T for characterization of an animal model of pulmonary embolism.

Methods

MRAs were performed in five rabbits using a 7-T MR scanner. Preceding the MR studies, each rabbit underwent a pulmonary artery catheterization with balloon placement. Two doses of gadodiamide were injected: first during a time-resolved MRA, immediately followed by a high-resolution acquisition. Balloon was then deflated, permitting reperfusion for 5 min. A second dose was then injected and another high-resolution MRA acquired. Measurements of signal-to-noise ratio (SNR), contrast-to-noise ratio (CNR) and vessel cross-sections down to fourth-order branches were made, among other parameters.

Results

Occlusion was detected in all rabbits. Despite a TE of 0.58 ms for the time-resolved MRA, regions of nonuniform enhancement attributed to susceptibility effects at the 7-T field were observed in perfused lung. Mean SNR=7.5±3.3 and 134.2±46.5 for the lung and aorta, respectively, and mean CNR=126.7±46.4 for aorta versus lung were obtained. Diameters of vessels in lung that was never occluded were not statistically different from those in reperfused lung.

Conclusion

Results show that time-resolved and high-resolution MRA of the lung are feasible at 7 T and provide high SNR, CNR and resolution, but TEs smaller than 0.58 ms are required to avoid susceptibility artifacts in time-resolved MRAs.     

High-resolution gadolinium-enhanced 3D MRA of the infrapopliteal arteries. Lessons for improving bolus-chase peripheral MRA

Peripheral magnetic resonance angiography (MRA) is growing in use. However, methods of performing peripheral MRA vary widely and continue to be optimized, especially for improvement in illustration of infrapopliteal arteries. The main purpose of this project was to identify imaging factors that can improve arterial visualization in the lower leg using bolus chase peripheral MRA. Eighteen healthy adults were imaged on a 1.5T MR scanner. The calf was imaged using conventional three-station bolus chase three-dimensional (3D) MRA, two dimensional (2D) time-of-flight (TOF) MRA and single-station Gadolinium (Gd)-enhanced 3D MRA. Observer comparisons of vessel visualization, signal to noise ratios (SNR), contrast to noise ratios (CNR) and spatial resolution comparisons were performed. Arterial SNR and CNR were similar for all three techniques. However, arterial visualization was dramatically improved on dedicated, arterial-phase Gd-enhanced 3D MRA compared with the multi-station bolus chase MRA and 2D TOF MRA. This improvement was related to optimization of Gd-enhanced 3D MRA parameters (fast injection rate of 2 mL/sec, high spatial resolution imaging, the use of dedicated phased array coils, elliptical centric k-space sampling and accurate arterial phase timing for image acquisition). The visualization of the infrapopliteal arteries can be substantially improved in bolus chase peripheral MRA if voxel size, contrast delivery, and central k-space data acquisition for arterial enhancement are optimized. Improvements in peripheral MRA should be directed at these parameters.     

Fluoroscopically triggered contrast-enhanced 3D MR DSA and 3D time-of-flight turbo MRA of the carotid arteries: first clinical experiences in correlation with ultrasound, x-ray angiography, and endarterectomy findings

The aim of this article was to obtain initial experiences with fluoroscopically triggered contrast-enhanced (CE) 3D MR DSA with elliptical centric k-space order and 3D time-of-flight (TOF) turbo MRA of the carotid arteries. In this prospective study we examined 16 consecutive patients with suspicion of atherosclerotic disease involving the carotid arteries. Ultrasound was available in all, x-ray angiography in 12, surgical correlation in 9, and intraoperative x-ray angiography in 4 patients. All examinations were done on a 1.5 T unit applying: transverse plain 3D TOF turbo MRA and coronal CE MRA with fluoroscopic triggering. Combining head and neck array coils allowed the visualization of supraaortic arteries from the aortic arch to the circle of Willis. MRA results (maximum intensity projections) were compared with x-ray angiography, ultrasound, and inspection of endarterectomy specimens. Volume rendering was performed in selected cases additionally. Agreement between CE MRA, 3D TOF turbo MRA and x-ray angiography regarding stenoses of the internal and external carotid artery was very good. CE MRA was able to detect correctly intracranial stenoses, but delineation of the aortic arch and proximal common carotid arteries was sometimes reduced. Volume rendering was suited for visualization of MRA images providing a realistic three-dimensional impression. In conclusion, high-resolution fluoroscopically triggered CE MRA as non-invasive technique is another important step on the way to replace invasive x-ray angiography for the evaluation of atherosclerotic carotid artery disease. High resolution 3D TOF turbo MRA might be a helpful adjunct to increase the diagnostic reliability for the carotid bifurcation.     

Comparative study of fast MR imaging: quantitative analysis on image quality and efficiency among various time frames and contrast behaviors

The purpose of this study is to quantitatively compare the image quality and efficiency provided by widely available fast MR imaging pulse sequences. A composite phantom with various T1 and T2 values and subjected to periodic motion was imaged at 1.5 T. The fast MRI sequences evaluated included fast spin-echo (FSE), single shot fast spin-echo (SSFSE), echo-planar imaging (EPI), multi-slice gradient recalled (MPGR), fast MPGR (FMPGR), and fast multi-slice spoiled gradient echo (FMPSPGR). T1-weighted (T1WI), T2-weighted (T2WI), proton-density-weighted (PDWI), and T2*-weighted (T2*WI) images were evaluated in breath-hold and non-breath-hold time frames. Analysis included measurement of image signal-to-noise ratio (SNR), contrast-to-noise ratio (CNR), nonuniformity, ghosting ratio, SNR per unit time and CNR per unit time. Among fast T2WI sequences, FSE with breath-hold time frame resulted in the highest image quality and in superior SNR and CNR efficiency by a factor of 5 or 6 as compared with conventional spin echo sequence. Among fast T1WI sequences, FMPGR and FMPSPGR both with non-breath-hold time frame produced the highest image quality and SNR and CNR efficiency by a factor of greater than 5 as compared with conventional spin echo. Among fast PDWI and T2*WI sequences, FSE produced the highest SNR and CNR, and was maximally efficient with a factors of greater than 6 as compared with conventional spin echo.     

Parallel imaging for first-pass myocardial perfusion

Two parallel imaging methods used for first-pass myocardial perfusion imaging were compared in terms of signal-to-noise ratio (SNR), contrast-to-noise ratio (CNR) and image artifacts. One used adaptive Time-adaptive SENSitivity Encoding (TSENSE) and the other used GeneRalized Autocalibrating Partially Parallel Acquisition (GRAPPA), which are both applied to a gradient-echo sequence. Both methods were tested on 12 patients with coronary artery disease. The order of perfusion sequences was inverted in every other patient. Image acquisition was started during the administration of a contrast bolus followed by a 20-ml saline flush (3 ml/s), and the next perfusion was started at least 15 min thereafter using an identical bolus. An acceleration rate of 2 was used in both methods, and acquisition was performed during breath-holding. Significantly higher SNR, CNR and image quality were obtained with GRAPPA images than with TSENSE images. GRAPPA, however, did not yield a higher CNR when applied after the second bolus. GRAPPA perfusion imaging produced larger differences between subjects than did TSENSE. Compared to TSENSE, GRAPPA produced significantly better CNR on the first bolus. More consistent SNR and CNR were obtained from TSENSE images than from GRAPPA images, indicating that the diagnostic value of TSENSE may be better.     

Magnetic resonance imaging of the abdominal aorta and iliac vessels using combined 3-D gadolinium-enhanced MRA and gadolinium-enhanced fat-suppressed spoiled gradient echo sequences.

This study evaluates a combined protocol consisting of breath hold immediate post gadolinium 3-D gradient echo MR angiography and blood pool phase gadolinium-enhanced breath hold 2-D fat-suppressed spoiled gradient echo (SGE) sequences in the examination of diseases of the abdominal aorta and iliac vessels. Thirty-two patients with suspected disease of the abdominal aorta, major aortic branches, or iliac vessels underwent MR angiographic study from January 1996 to January 1997. Examinations were performed on a 1.5 T MR imager using 2-D axial SGE, coronal 3-D fast imaging in steady state precession (3-D FISP) following bolus administration of 40 mL of gadolinium, and axial and coronal blood pool phase gadolinium-enhanced fat-suppressed SGE. Post-processed data, including 3-D reconstructions using maximum intensity projection (MIP), targeted MIP, and multiplanar reconstruction (MPR) were evaluated. MR findings in all patients were correlated as follows: surgery (13 patients), angiography (11 patients), contrast enhanced CT (3 patients), non-contrast enhanced CT (1 patient), color doppler US (2 patients), and previous MR study (2 patients). MR findings correlated closely with findings at surgery or other imaging studies in 31 of 32 patients. One patient had renal artery occlusion that was misinterpreted as mild stenosis. The following vascular diseases were present: aneurysm disease [10 patients: aortic aneurysm (8 patients), inflammatory aneurysm (2 patients)], thoracoabdominal aortic dissection (2 patients), arteriovenous fistula (1 patient), stenoses and/or occlusion of the abdominal aorta, major aortic branches and iliac vessels [12 patients: stenoses and/or occlusion of the abdominal aorta with stenoses of the iliac vessels (9 patients), renal artery stenosis (2 patients), occlusion of the abdominal aorta (1 patient)], and occluded artery to pancreatic transplant artery (1 patient). Five patients had normal studies. The 3-D FISP technique accurately defined the luminal contours of vessels, allowing precise depiction of vessel stenosis (i.e., renal artery stenosis or common iliac artery stenosis) and clear demonstration of relationship of aortic branch vessels (i.e., renal arteries) to underlying aortic pathology (i.e., aortic aneurysm or dissection). Blood pool phase gadolinium-enhanced fat-suppressed SGE images were useful in the evaluation of the external surface of vessel walls, and providing accurate measurement of aneurysm diameter and other associated vascular entities (i.e., inflammatory aneurysm, left-sided IVC). Targeted MIP or MPR reconstruction were important for assessing stenoses of medium sized vessels such as renal arteries and branches of the iliac arteries, and for identifying accessory arteries. The combination of immediate post gadolinium 3-D FISP and blood pool phase gadolinium-enhanced fat-suppressed SGE is useful in the evaluation of the abdominal aorta, major aortic branches and iliac vessels. Immediate post gadolinium 3-D FISP images provides diagnostically useful information regarding vessel luminal contour, while blood pool phase gadolinium-enhanced fat-suppressed SGE provides ancillary information on the vessel wall and surrounding tissue.     

Single breath-hold multi-slab and cine cardiac-synchronized gadolinium-enhanced three-dimensional angiography

The rest period of the coronary arteries has been shown to be on the order of 120–160 msec. Restriction of the acquisition window in breath-hold cardiac-synchronized gadolinium-enhanced imaging to this duration limits the amount of sampled k-space data and hence the information when compared with conventional gadolinium-enhanced imaging. Two techniques for gadolinium-enhanced cardiac-synchronized angiography were implemented that acquire additional data during the unused portions of the cardiac cycle. Data acquisition is synchronized with the heart cycle and is restricted to a short period of each heart cycle. In a single breath-hold, a multi-slab acquisition (n = 5) allowed ECG-synchronized imaging of the entire heart or a CINE acquisition (n = 5) provided multiple stacks of images at different phases in the cardiac cycle over a smaller area. Preliminary results acquired in healthy volunteers and patients with aortic disease indicate that additional information can be acquired without an increase in breath-hold duration or a reduction in image quality.     

Electrocardiograph-triggered two-dimensional time-of-flight versus optimized contrast-enhanced three-dimensional MR angiography of the peripheral arteries

We determined whether the accuracy of magnetic resonance angiography (MRA) in the peripheral run-off vessels can be improved by using contrast-enhanced (CE) three-dimensional (3D) technique in comparison to electrocardiograph (ECG)-triggered two-dimensional (2D) time-of-flight (TOF) technique. In a prospective study 20 patients with occlusions of the pelvic and/or femoral arteries underwent a CE 3D MRA (repetition time (TR): 5 ms, (TE) echo time: 2 ms, flip angle (FA): 30°) and an ECG-triggered 2D time-of-flight (TOF) technique (TR: 408 resp. 608 ms, TE: 7 ms, FA: 70°) of the run-off vessels on a 1.5 T MR system. Each patient received a contrast material volume of 0.15 mmol/kg of body weight of gadolinium (Gd)/DTPA using an automatic injector. The tube system to the patient was flushed by 50 mL of a saline solution applied with the same injection rate as the contrast material administration. The start of the 3D MR sequence was tailored individually to the applied contrast material after determination of circulation times by a prior bolus. All patients underwent each conventional or digital arteriography for comparison, as well. The visualization of the run-off vessels was ranked on a scale of 0–3 (0 = poor, 1 = fair, 2 = good, 3 = excellent) by three blinded reviewers. They also graded the vascular segments as either occluded or significantly altered (>50% reduction in diameter) or free of significant stenosis. CE 3D MRA was significantly faster in imaging the run-off vessels in comparison to the ECG-triggered 2D TOF technique. All 160 vascular segments were visualized with the 3D method, whereas only 142/160 segments were seen with 2D technique. The resulting image quality ranking of all vascular segments was significantly higher (p < 0.05) using CE 3D MRA (2.8) than with the 2D TOF technique (2.4). The detection of the stenoses was possible with both techniques. The grading of seven of seven stenoses was correct with 3D method and in five of seven cases with the 2D TOF technique. All vessel occlusions were detected by using both techniques. Small collaterals were visualized in more detail with the CE 3D MR angiography. These data demonstrate an improvement in image quality and accuracy of MRA of the peripheral arteries using a CE 3D technique in comparison to an ECG-triggered 2D TOF sequence.     

MRI of liver: a comparison of CNR enhancement using high dose and low dose ferumoxide infusion in patients with colorectal liver metastases

The purpose of this study was to compare the effects of high dose (HD) and low dose (LD) ferumoxides infusions on lesion-to-liver contrast-to-noise ratio (CNR) using four different T(2)-weighted MR sequences. Seventy-three patients with known colorectal liver metastases underwent T(2)-weighted fast spin echo (FSE) imaging before and after ferumoxides. After ferumoxides, T(2)-weighted dual echo (DE) and T(2)-weighted GRE FLASH images were also obtained. To evaluate the relationship between TE length and lesion-to-liver CNR, the same FLASH sequence was repeated in 18 LD patients after lengthening the TE. Ferumoxides was administered at a dose of 15 micromol/kg (HD) and 7.5 micromol/kg (LD) in 45 and 28 patients, respectively. The effects of HD and LD ferumoxides infusions were measured as the percentage signal intensity change (PSIC) in the liver and lesions, lesion-to-liver CNR and the change in lesion-to-liver CNR (DeltaCNR). In both LD and HD groups, all CNR values obtained after SPIO were significantly greater than those observed with unenhanced FSE (p < 0.01). There was no significant difference between the mean CNR values obtained with either dose for any sequence. With the FLASH sequence, CNR increased progressively with longer TE. At the longest TE of 26 ms, mean CNR was higher than that recorded with any of the other sequences. Although mean liver PSIC was significantly greater in the HD group than in the LD group (p < 0.01) because the mean lesion PSIC was also greater in the HD group, the mean DeltaCNR after ferumoxides was not significantly different in the two groups. LD SPIO enhanced MR significantly increases lesion-to-liver CNR compared with unenhanced images. At 1. 0 T, HD and LD ferumoxides infusions produce comparable lesion-to-liver CNR. Our results suggest that at 1.0 T ferumoxides may be administered at a dose of 7.5 micromol/kg without loss of image quality.     

Quantification and improvement of the signal-to-noise ratio in a magnetic resonance image acquisition procedure

A procedure is developed to quantify and improve the signal-to-noise ratio (SNR) of magnetic resonance images. The image SNR is quantified using the correlation function of two independent acquisitions of an image. To test the performance of the quantification, SNR measurement data are fitted to theoretically expected curves. The proposed correlation technique is also used to improve the SNR by estimating the amplitude of the signal spectrum. The technique is applied to a set of MR images, and its performance in terms of gain in SNR, contrast-to-noise ratio (CNR), and resolution loss is compared to that of classical noise filters. The SNR as well as the CNR is improved significantly with minor loss of resolution. Finally, it is shown that the correlation technique can be implemented in a highly efficient way in almost any acquisition procedure of a magnetic resonance imaging system.     

Multichannel transceiver dual-tuned RF coil for proton/sodium MR imaging of knee cartilage at 3 T

Sodium magnetic resonance (MR) imaging is a promising technique for detecting changes of proteoglycan (PG) content in cartilage associated with knee osteoarthritis. Despite its potential clinical benefit, sodium MR imaging in vivo is challenging because of intrinsically low sodium concentration and low MR signal sensitivity. Some of the challenges in sodium MR imaging may be eliminated by the use of a high-sensitivity radiofrequency (RF) coil, specifically, a dual-tuned (DT) proton/sodium RF coil which facilitates the co-registration of sodium and proton MR images and the evaluation of both physiochemical and structural properties of knee cartilage. Nevertheless, implementation of a DT proton/sodium RF coil is technically difficult because of the coupling effect between the coil elements (particularly at high field) and the required compact design with improved coil sensitivity. In this study, we applied a multitransceiver RF coil design to develop a DT proton/sodium coil for knee cartilage imaging at 3 T. With the new design, the size of the coil was minimized, and a high signal-to-noise ratio (SNR) was achieved. DT coil exhibited high levels of reflection S11 (～-21 dB) and transmission coefficient S12 (～-19 dB) for both the proton and sodium coils. High SNR (range 27-38) and contrast-to-noise ratio (CNR) (range 15-21) were achieved in sodium MR imaging of knee cartilage in vivo at 3-mm(3) isotropic resolution. This DT coil performance was comparable to that measured using a sodium-only birdcage coil (SNR of 28 and CNR of 20). Clinical evaluation of the DT coil on four normal subjects demonstrated a consistent acquisition of high-resolution proton images and measurement of relative sodium concentrations of knee cartilages without repositioning of the subjects during the same MR scanning session.     

Development of a 0.014-in., anti-solenoid loop MR imaging guidewire for intravascular 3.0-T MR imaging

Purpose

This study aimed to develop a 0.014-in., anti-solenoid loop (ASL) magnetic resonance imaging guidewire (MRIG) for intravascular 3.0-T MR imaging.

Materials and Methods

We first designed the ASL MRIG, which was made of a coaxial cable with its extended inner conductor and outer conductor connected to two micro-anti-solenoids. We then evaluated in vitro the functionality of the ASL MRIG by imaging a “vessel” in a phantom and achieving signal-to-noise ratio (SNR) and SNR contour map of the new 0.014-in. ASL MRIG. Subsequently, we validated in vivo the feasibility of using the ASL MRIG to generate intravenous 3.0-T MR images of parallel iliofemoral arteries of near-human-sized living pigs.

Results

In vitro evaluation showed that the 0.014-in. ASL MRIG functioned well as a receiver coil with the 3.0-T MR scanner, clearly displaying the vessel wall with even distribution of MR signals and SNR contours from the ASL MRIG. Of the in vivo studies, the new ASL MRIG enabled us to successfully generate intravenous 3.0-T MR imaging of the iliofemoral arteries.

Conclusion

This study confirms that it is possible to build such small-looped MRIG at 0.014 in. for intravascular 3.0-T MR imaging.     

Detecting sub-voxel microvasculature with USPIO-enhanced susceptibility-weighted MRI at 7 T

BackgroundSusceptibility weighted imaging (SWI) combines phase with magnitude information to better image sub-voxel veins. Recently, it has been extended to image very small sub-voxel arteries and veins by injecting intravenously the ultra-small superparamagnetic iron oxide, Ferumoxytol.ObjectiveTo determine practical experimental imaging parameters for sub-voxel cerebral vessels at 7 T.MethodsSix Wistar-Kyoto rats aged 7–13 weeks were imaged. For a given spatial resolution, SWI was acquired pre- and post- Ferumoxytol with doses of 2, 4, 6 and 8 mg/kg and echo times (TEs) of 5, 10 and 15 ms at each dose. The spatial resolutions of 62.5 × 125 × 250 μm³ (acquisition time of 7.5 min) and 62.5 × 62.5 × 125 μm³ (30 min) were used. Both SWI and quantitative susceptibility mapping (QSM) data were analyzed. Contrast-to-noise ratio (CNR) was measured and used to determine the optimal practical imaging parameters for detection of small cortical penetrating arteries.ResultsFor a given spatial resolution with an aspect ratio (frequency: phase: slice) of 2:4:8 relative to the vessel size, we found the TE-dose index (TE x dose) must be at least 40 ms·mg/kg for both SWI and QSM to reveal the most vessels. The higher the TE-dose index, the better the image quality for both SWI and QSM up to 60 ms·mg/kg.ConclusionsThere is an optimal TE-dose index for improved visualization of sub-voxel vessels. Choosing the smallest TE and the largest allowed dose made it possible to run the sequence efficiently. In practice, the aspect ratio of 2:4:8 and the TE-dose index ranging from 40 to 60 ms·mg/kg provided the optimal and most practical solution.     

Flip Angle for the Optimal <Emphasis Type="Italic">T</Emphasis><Subscript>1</Subscript>-weighted Image in the 3-D Volumetric Interpolated Breath-hold Examination Abdominal Magnetic Resonance Imaging Technique

The purpose of this study was to determine an optimal flip angle for T ₁-weighted images on abdominal examination by comparing the signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR) depending on the change in flip angle based on the volumetric interpolated breath-hold examination (VIBE) technique. The subjects in this study included 50 patients (20 men and 10 women; average age, 60 years) who visited the hospital between October 2009 and March 2010 to receive an abdominal magnetic resonance imaging (MRI) examination. Among the 50 patients, there were 27 patients with hypervascular hepatocellular carcinomas (HCCs) and 23 patients with hemorrhagic HCCs. A 3 T MR scanner (Magnetom Tim Trio; Siemens, Germany) with a 12-channel body coil was used. For the pulse sequence, the VIBE (time of repetition TR, 3.18 ms; time of echo TE, 1.16 ms; matrix, 384 × 307; slice thickness, 3 mm; field of view FOV, 380 mm; bandwidth BW, 720 Hz) and breath-hold examination with an examination time of 19 s were used. Images of the axial and coronal planes at three flip angles (10°, 25°, and 35°) were obtained. Based on the images obtained, the signal intensities of the liver, lesions, and background noise were measured and the SNR and CNR were calculated. For evaluation of the optimal flip angle, SPSS for Windows (version 17.0) was used to conduct the non-parametric Kruskal–Wallis test. The SNRs for hypervascular and hemorrhagic HCCs, depending on changes in flip angle of the VIBE, were 11.12 ± 0.98, 10.83 ± 1.44, and 9.61 ± 1.66, and 76.00 ± 6.43, 43.32 ± 5.89, and 30.45 ± 4.27 at angles of 10°, 25°, and 35°, respectively. The CNRs were 14.83 ± 0.12, 7.38 ± 0.41, and 5.70 ± 0.66, and 3.95 ± 0.21, 2.42 ± 0.58, and 1.69 ± 0.93, respectively (p < 0.05). At a flip angle of 10°, the SNR and CNR were the highest. When the flip angles were 25° and 35°, the contrast of the image, as well as the SNR, were shown to have a downward trend (p < 0.05). A flip angle of 10° is considered to be useful for the optimal T ₁-weighted image to detect HCC in the three-dimensional VIBE abdominal MRI technique.     

Large angle spin-echo imaging

A study was undertaken to assess the use of excitation flip angles greater than 90° for T₁ weighted spin-echo (SE) imaging with a single 180° refocusing pulse and short TR values. Theoretical predictions of signal intensity for SE images with excitation pulse angles of 90–180° were calculated based on the Bloch equations and then measured experimentally from MR images of MnCl₂ phantoms of various concentrations. Liver signal-to-noise ratios (SNR) and liver-spleen contrast-to-noise ratios (CNR) were measured from breathhold MR images of the upper abdomen in 16 patients using 90 and 110° excitation flip angles. The theoretical predictions showed significant improvements in SNR with excitation flip angles >90°, which were more pronounced at small TR values. The phantom studies showed reasonably good agreement with the theoretical predictions in correlating the excitation pulse angle with signal intensity. In the human imaging studies, the 110° excitation pulse angle resulted in a 7.4% (p < .01) increase in liver SNR and an 8.2% (p = .2) increase in liver-spleen CNR compared to the 90° pulse angle at TR = 275 ms. Increased signal intensity resulting from the use of large flip angle excitation pulses with a single echo SE pulse sequence was predicted and confirmed experimentally in phantoms and humans.     

Intravascular 3.0 T MRI Using an Imaging-Guidewire: a Feasibility Study in Swine

This study was to validate the feasibility of using a magnetic resonance imaging-guidewire (MRIG) for intravascular 3.0 T MR imaging of deep-seated arterial walls of large animals. The functionality of a 0.032-in. MRIG was evaluated and the signal-to-noise ratio (SNR) was calculated. Then, MRI of ten iliofemoral arteries of six pigs was acquired by MRIG and surface coil. The difference in the SNRs of the arterial walls between different coils was compared. Histology examined the potential thermal injuries of the imaged vessels. The MRIG functioned with the 3.0 T MR scanner. The average SNR of the arterial walls was significantly higher with the MRIG than with the surface coils (76.22 ± 34.76 vs. 12.63 ± 4.25, P < 0.01). Histology showed no evidence of thermal injuries at the vessel walls. This study validated the feasibility of generating intravascular 3.0 T MRI of deep-seated arterial walls in large animals, which should facilitate the translation of this technique from 1.5 to 3.0 T MR scanner.     

The value of single-shot black-blood MR imaging for mapping of the coronary arteries: a comparison of four different orientations during breath-holding and free breathing

The value of ECG-gated single-shot black-blood MR imaging for rapid visualization of the origin and course of the coronary arteries was investigated. The study population included 28 patients with known or suspected cardiac disease. ECG-gated single-shot black-blood MR acquisitions were acquired in the transverse, coronal, sagittal and LAO orientations, during free breathing and breath-holding. The origin of the left coronary artery was most frequently visualized in the coronal and LAO orientations and the origin of the right coronary artery was most frequently visualized in the LAO orientation. Overall, no significant difference was found for the visualization of the coronary artery segments and the overall image quality among acquisitions during breath-holding and free breathing. ECG-gated single-shot black-blood MR imaging (HASTE) appears to be a time-efficient and robust method for mapping of the entire coronary artery tree, without the need for breath-holding. The LAO orientation provides the most consistent visualization of the origins and major coronary artery segments.     

A 3D balanced-SSFP Dixon technique with group-encoded k-space segmentation for breath-held non-contrast-enhanced MR angiography

A three-dimensional balanced steady-state free precession (b-SSFP)-Dixon technique with a novel group-encoded k-space segmentation scheme called GUINNESS (Group-encoded Ungated Inversion Nulling for Non-contrast Enhancement in the Steady State) was developed. GUINNESS was evaluated for breath-held non-contrast-enhanced MR angiography of the renal arteries on 18 subjects (6 healthy volunteers, 12 patients) at 3.0 T. The method provided high signal-to-noise and contrast renal angiograms with homogeneous fat and background suppression in short breath-holds on the order of 20 s with high spatial resolution and coverage. GUINNESS has potential as a short breath-hold alternative to conventional respiratory-gated methods, which are often suboptimal in pediatric subjects and patients with significant diaphragmatic drift/sleep apnea.