half-Fourier Single-shot Turbo Spin-echo Research Articles

Resolution enhancement in single-shot imaging using simultaneous acquisition of spatial harmonics (SMASH).

Spatial resolution in single-shot imaging is limited by signal attenuation due to relaxation of transverse magnetization. This effect can be reduced by minimizing acquisition times through the use of short interecho spacings. However, the minimum interecho spacing is constrained by limits on gradient switching rates, radiofrequency (RF) power deposition and RF pulse length. Recently, simultaneous acquisition of spatial harmonics (SMASH) has been introduced as a method to acquire magnetic resonance images at increased speeds using a reduced number of phase-encoding gradient steps by extracting spatial information contained in an RF coil array. In this study, it is shown that SMASH can be used to reduce the effects of relaxation, resulting in single-shot images with increased spatial resolution without increasing imaging time. After a brief theoretical discussion, two strategies to reduce signal attenuation and increase spatial resolution in single-shot imaging are introduced and their performance is evaluated in phantom studies. In vivo single-shot echoplanar imaging (EPI), BURST, and half-Fourier single-shot turbo spin-echo (HASTE) images are then presented demonstrating the practical implementation of these resolution enhancement strategies. Images acquired with SMASH show increased spatial resolution and improved image quality when compared with images obtained with the conventional acquisitions. The general principles presented for imaging with SMASH can also be applied to other partially parallel imaging techniques.

MR imaging of pulmonary parenchyma with a half-Fourier single-shot turbo spin-echo (HASTE) sequence

Objective: To evaluate the utility of a half-Fourier single-shot turbo spin-echo sequence (HASTE) at depicting lung parenchyma and lung pathology. Methods and patients: A HASTE sequence was applied to five normal volunteers and 20 patients with various pulmonary disorders to depict the lung parenchyma. Images were acquired with ECG-triggering and breath-holding. In three volunteers, signal intensity measurements from lung parenchyma were performed using four sequences: (a) HASTE; (b) conventional spin echo; (c) fast spin echo; and (d) gradient echo. T2 maps were produced using the HASTE acquisition. Results: Minimal respiratory or cardiac motion artifacts were observed. The signal-to-noise ratios from lung parenchyma were 27.8±5.4, 22.0±3.0, 15.3±0.9, and 6.0±1.9 for HASTE, spin-echo, fast spin-echo, and gradient echo sequences, respectively. The scan time for HASTE was 302 ms for each slice. The T2 values in the right lung and the left lung were 61.2±4.1 and 79.1±8.9 ms in systole and 92.6±5.8 and 97.5±12.2 ms in diastole, respectively ( P<0.05 diastole versus systole). The HASTE sequence demonstrated clearly various pulmonary disorders, including lung cancer, hilar lymphadenopathy, metastatic pulmonary nodules as small as 3 mm, pulmonary hemorrhage, pulmonary edema and bronchial wall thickening in bronchiectasis. Conclusion: Our preliminary results indicate that the HASTE sequence provides a practical means for breath-hold MR imaging of lung parenchyma.

Prenatal magnetic resonance imaging enhances fetal diagnosis

Background: Ultrasound (US) evaluation of some fetal anomalies provides limited information. Anatomic details that affect prognosis and selection for fetal therapy, such as liver herniation and pulmonary hypoplasia in congenital diaphragmatic hernia (CDH) and airway patency in giant neck masses, may be difficult to delineate using conventional sonographic methods. The authors evaluated the utility of prenatal magnetic resonance imaging (MRI) with new ultrafast imaging sequences in the diagnosis and management of fetal anomalies. Methods: From April 1996 to April 1997 45 MRI scans were performed in 31 pregnant women with an US diagnosis of a fetal anomaly. The US diagnoses included CDH, giant neck masses, lung masses, abdominal and pelvic abnormalities, twin anomalies, and central nervous system (CNS) anomalies. The fetuses ranged in age from 18 to 39 weeks' gestation (mean, 28.7 weeks). Using a 1.5-T magnet, a variety of ultrafast imaging sequences were performed including fast gradient-echo, half-fourier single shot turbo spin-echo (Haste) and echo-planar imaging yielding images with T 1 to T 2 type weighting. Results: With CDH, MRI demonstrated liver herniation into the chest in 11 of 14 cases. In four cases, US findings had not been definitive. In two cases of CDH detected by MRI, the primary diagnosis by US had been congenital cystic adenomatoid malformation (CCAM). With lung masses, MRI accurately distinguished between CCAM and bronchopulmonary sequestration (BPS). For giant neck masses with potential airway obstruction, MRI scans permitted differentiation of teratoma from cystic hygroma and allowed delineation of fetal airway involvement. The accurate anatomic evaluation facilitated planning for the ex utero intrapartum treatment (EXIT) procedure, a technique for securing the airway while the term fetus is still on placental support. With huge abdominal masses such as enterogenous cyst and lymphangioma, MRI scanning clarified the diagnosis. Fourteen of the 31 (45%) patients underwent fetal treatment after US and MRI evaluation. Conclusions: Prenatal MRI enhances fetal anatomic evaluation and facilitates perinatal management and family counseling. Ultrafast imaging sequence MRI is helpful to corroborate and refine US diagnoses. Fetal MRI is a valuable adjunct to US for prenatal diagnosis before fetal surgical intervention for selected life-threatening birth defects.

Imaging of gallbladder and biliary tract before laparoscopic cholecystectomy: Comparison of intravenous cholangiography and the combined use of haste and single-shot rare MR imaging : Vanbeckevoort D, Van Hoe L, Ponette E, et al. (Department of Radiology, University Hospitals, Herestraat 49, B-Leuven, Belgium). J Belge Radiol 1997;80:6–8

To compare intravenous cholangiography (i.v.c.) and magnetic resonance imaging (MRI) as preoperative imaging techniques in patients scheduled for laparoscopic cholecystectomy. Twenty patients underwent i.v.c. and MRI, 40 axial 'localizer' images were first obtained with a half-Fourier single-shot turbo spin echo (HASTE) sequence. Next, an extremely high T2-weighted rapid acquisition relaxation enhancement (RARE) acquisition (TE = 1100 msec) was used for MR cholangiography. All images obtained with i.v.c. and MRI were independently analyzed by two observers. The relative visibility of the (normal or abnormal) gallbladder (GB), cystic duct (CD), and bile ducts (BD) on both types of images was scored as follows: 1 = MRI better than i.v.c.; 2 = no difference; 3 = i.v.c. better than MRI. We observed 3 anatomic variants: 1 of the cystic duct and 2 of the intrahepatic bile ducts; 15 patients had gallstones; one had cholecystitis. Magnetic resonance images were considered more informative than i.v.c.-images for visualization of GB in 11 patients (55%), for CD in 9 patients (45%), and in 8 patients (40%) for visualization of the CBD. Intravenous cholangiography outperformed MRI in the evaluation of the CBD and CD in one patient (5%). The combined use of half-Fourier single-shot RARE and high T2-weighted RARE MR imaging is a valuable alternative to i.v.c. in the preoperative evaluation of gallbladder and biliary tract.

Rapid T2-weighted MR imaging of uterine leiomyomaand adenomyosis

To compare three rapid T2-weighted pulse sequences with high-resolution turbo spin-echo (SE) magnetic resonance (MR) imaging for the diagnosis of leiomyoma and adenomyosis. Eighteen patients referred for evaluation of suspected leiomyoma or adenomyosis underwent imaging at 1.5 T with a phased-array multicoil. Non-breath-hold, fat-saturated sagittal images of 4-7 mm, with equivalent voxel size, were obtained through the pelvis with the following three rapid pulse sequences: segmented, half-Fourier single shot turbo SE (HASTE), turboGRASE (TGSE) and turbo SE MR images. Mean acquisition times were 17 s (HASTE), 37 s (TGSE), and 42 s (turbo SE). These images were compared, in a blinded fashion, to high resolution turbo SE MR images, which are considered the "standard" for pelvic MRI. The three rapid pulse sequences, HASTE, TGSE and turbo SE, provided equivalent diagnostic information when compared with high-resolution turbo SE MR images. There was no significant difference in image quality, detection and localization of leiomyoma or in diagnosis of adenomyosis among the three rapid sequences. HASTE imaging demonstrated the least ghosting. Diagnostic T2-weighted images of benign uterine pathology may be obtained in as little as 17 s.

Left-sided congenital diaphragmatic hernia: value of prenatal MR imaging in preparation for fetal surgery.

To evaluate the usefulness of prenatal magnetic resonance (MR) imaging in determination of the position of the fetal liver and amount of lung tissue in left-sided congenital diaphragmatic hernia. In three pregnant women, MR imaging was performed with a 1.5-T magnet and fast gradient-echo, half-Fourier single-shot turbo spin-echo, and echo-planar sequences. MR imaging findings were compared with those from ultrasound (US) performed the same day. The fetuses were 20, 23, and 32 weeks gestational age. The fetal liver was demonstrated in the chest in all three fetuses with MR imaging and in only one fetus with US. The best images of the fetal liver were obtained with a T1-weighted gradient-echo sequence. The best images of the entire fetus were obtained with a half-Fourier single-shot turbo spin-echo sequence. In these fetuses, MR imaging proved important by clearly demonstrating herniation of fetal liver into the chest, thereby changing family counseling and prenatal care.

Preliminary experience with a new double-echo half-Fourier single-shot turbo spin echo acquisition in the characterization of liver lesions.

A new double-echo half-Fourier single-shot turbo spin echo technique has been implemented in which two images are obtained per excitation pulse, one with an echo time (TE) of 60 ms and another with a TE of 438 ms. The acquisition window per image is 380 ms and is determined by the echo spacing of 4.3 ms and the echo train length of 88 for images with resolution of 160 x 256. No breath holding was performed. The aim of the study was to test whether the additional information of the late TE image improves the characterization of liver lesions. Twenty-eight patients with 39 focal liver lesions (9 cysts, 11 hemangiomas, and 19 solid lesions) were imaged with the new technique, and signal intensity (SI) ratios of lesion and liver were obtained. A t-test analysis showed that in the TE 60 ms image, SI ratios of cysts and hemangiomas were not significantly different, whereas in the TE 438 ms images the two types of lesions can be classified. Signal intensity ratios of solid lesions were in both images clearly lower than those of cysts and hemangiomas. The technique, therefore, seems a promising and straightforward new tool for the characterization of liver lesions.

Single-shot T1- and T2-weighted magnetic resonance imaging of the heart with black blood: preliminary experience.

To implement and evaluate two robust methods for T1- and T2-weighted snapshot imaging of the heart with data acquisition within a single heart beat and suppression of blood signal. Both T1- and T2-weighted diastolic images of the heart can be obtained with half Fourier single-shot turbo spin echo (HASTE) and turbo fast low-angle shot (turboFLASH) sequences, respectively, in less than 350 ms. Signal from flowing blood in the ventricles and large vessels can be suppressed by a preceding inversion recovery preparing pulse pair (PRESTO). Fifteen volunteers and five patients have been evaluated quantitatively for signal-to-noise ratio (SNR) contrast-to-noise ratio (CNR) and flow void and qualitatively for image quality, artifacts, and black-blood effect. Both PRESTO-HASTE and PRESTO-turboFLASH achieved consistently good image quality and blood signal suppression. In contrast to gradient-echo (GRE) echo-planar imaging techniques, (EPI) HASTE and turboFLASH are much less sensitive to local susceptibility differences in the thorax, resulting in a more robust imaging technique without the need for time-consuming system tuning. Compared to standard spin-echo sequences with cardiac triggering. HASTE and turboFLASH have significantly shorter image acquisition times and are not vulnerable to respiratory motion artifacts. PRESTO-HASTE and PRESTO-turboFLASH constitute suitable methods for fast and high-quality cardiac magnetic resonance imaging (MRI).

HASTE MR imaging: description of technique and preliminary results in the abdomen.

HASTE (Half fourier Single-shot Turbo spin-Echo) is a single-section T2-weighted sequence that acquires images in less than 1 second. Images are breathing independent and possess a variety of other features useful for imaging the abdomen. The design of this technique is described. Clinical studies of 38 consecutive patients were performed using this technique. HASTE images were considered good in 28 and fair in 10 patients, including five patients who could not suspend respiration. Definition of liver and bowel was particularly clear.