Diffusion-weighted MRI in prostate cancer -- comparison between single-shot fast spin echo and echo planar imaging sequences

Diffusion-weighted (DW) MRI at 1.5 T was carried out in two groups of patients. MRI data were correlated with the biopsy and histopathology (where available). The performance of two sequences -- a single-shot FSE (14 patients) and a single-shot EPI (15 patients) -- was compared. Average ADC values from the normal peripheral zone (PZ), central gland (CG) and the tumour [prostate carcinoma (PCa)] were calculated from b values of 0 and 600. Tukey-Kramer test was used for statistical analysis. EPI produced higher values of ADC (10(-3) mm(2)/s) than FSE sequence: 1.992+/-0.208 vs. 1.573+/-0.270 in PZ (P<.001), 1.518+/-0.126 vs. 1.373+/-0.179 in CG and 1.214+/-0.254 vs. 0.993+/-0.158 in PCa (P<.01). In conclusion, both EPI and FSE sequences showed differences in ADC between normal PZ, CG and PCa; however, EPI produced significantly higher ADC values than FSE.     

Magnetic resonance cholangiopancreatography: comparison between respiratory-triggered turbo spin echo and breath hold single-shot turbo spin echo sequences

The purpose of this study was to compare the relative conspicuity of the pancreaticobiliary tree on respiratory-triggered three-dimensional turbo spin echo (3D TSE RT) and breath hold single-shot turbo spin echo (SSTSE BH) acquisitions respectively in MRCP imaging. Both techniques were applied to 61 patients with clinically suspected pancreaticobiliary disease using a 1.0 T MR system. All images were reviewed blindly. Qualitative comparison was made by grading subjectively the conspicuity of extrahepatic, intrahepatic, and main pancreatic ducts. Quantitative comparison included calculations of signal-to-noise ratio of the common bile duct, main pancreatic duct, gallbladder, liver, and contrast-to-noise ratio, relative contrast between common bile duct, gallbladder, and liver. 3D TSE RT provided significantly higher signal-to-noise ratio of the common bile duct (mean value 163.19) and main pancreatic duct (mean value 95.37) compared to SSTSE BH (mean values 76.24 and 26.22, respectively). 3D TSE RT was inferior to SSTSE BH for the depiction of intrahepatic ducts and pancreatic duct (head portion). 3D TSE RT and SSTSE BH sequences provide complimentary information in the visualization of the biliary and pancreatic ducts. Further comparative clinical studies are needed to redefine the sensitivity, specificity, and accuracy of MRCP using both sequences.     

A comparison of fast spin echo and gradient field echo sequences

Optimal angle, fast repeat time, gradient field echo imaging techniques such as FISP (Fast Imaging with Steady Precession) and FLASH (Fast Low Angle Shot) often fail to discriminate disease from healthy tissue for two main reasons. First, T1 and T2 of the affected tissue may increase such that the ratio of T1 to T2 remains nearly unchanged, hence there is no contrast change with FISP. Second, T2 weighted gradient field echo images suffer severely from T2* signal and resolution loss leading to a reduction in C/N. Although FLASH imaging with two separate angles can, in principle, extract the longer T1 tumors, contrast is often not good. To overcome the inhomogeneity and contrast problems, we have implemented a FAst optimal angle spin-echo sequence with a short TE(FATE). For the first echo, FATE has the same contrast properties as FLASH with a slight decrease in signal intensity. The advantage is that the intensity of the signal does not suffer from T2* signal decay, hence improved contrast and disease detection via T2 weighted FATE images is possible. Contrast-to-noise in lesion detection is also considered for CE FAST (Contrast Enhanced Fast), a T2-weighted version of FISP, and HYBRID.     

Cervical spine MR imaging using multislice gradient echo imaging: comparison with cardiac gated spin echo

Forty-one patients with suspected cervical spine disorders were studied using multislice gradient echo imaging (GE) technique, with a 1.5-T system. The images were compared to cardiac-gated spin echo (CGSE) images in the diagnosis of suspected cord and spinal disorders. Images were graded for ability to detect cord lesion, cord-CSF contrast, CSF-bone contrast and contrast between CSF and extradural abnormality. The signal-to-noise ratio and contrast-to-noise ratio were used to compare images. There was 44% decrease in contrast between cord lesion and normal cord on GE when compared to CGSE, except for spinal cord hemorrhage. There was a 40% improvement between bone and CSF contrast on GE compared to CGSE. GE images were significantly better qualitatively as well as quantitatively in the detection of extradural lesions. This effect was more marked in axial plane where CGSE images are extremely suboptimal. CGSE images are better than GE for spinal cord lesions, while GE are superior in the diagnosis of degenerative disease in the cervical spine.     

Comparison of dual spin echo echo planar imaging (SE_EPI), turbo spin echo with fat suppression and conventional dual spin echo sequences for T(2)-weighted MR imaging of focal liver lesions

The performance of T(2)-weighted spin-echo version of echo planar imaging (SE_EPI), conventional spin echo (SE) and fat-suppressed turbo spin-echo (TSE_SPIR) sequences for the detection of focal liver lesions was evaluated. Twenty patients that were included in our study, had CT examinations prior to the MR study and were scheduled for surgery for removal of liver lesions. All patients had intraoperative sonographic examinations. Qualitative and quantitative analysis of the images was performed. Overall image quality of SE_EPI sequences was better than SE (p<0.001) and similar to TSE_SPIR sequences. There were fewer motion and ghost artifacts on SE_EPI and TSE_SPIR images compared to SE images (p<0.001). Susceptibility artifacts were statistically equivalent on SE_EPI and SE images (p<0.001) while chemical shift artifacts were equally observed on SE and SE_EPI sequences. Overall image quality of EPI-SE and TSE_SPIR sequences was better compared to SE sequences. There was no significant difference in the number of lesions detected by each of the three sequences. Quantitative analysis showed that liver/lesion contrast-to-noise ratio (CNR) and signal-to-noise ratio (SNR) of liver, lesion, spleen was higher on TSE_SPIR sequences (p<0.001) while SE_EPI and SE sequences showed non-significant differences (p>0.05). SE_EPI sequences of the liver resulted in fewer artifacts and shorter acquisition times than SE sequences. They provide a diagnostic performance similar to TSE_SPIR and better than that of SE sequences.     

Limited field of view spin echo MR imaging

Several groups have reported using a method of limiting the field of view (FOV) where the slices excited by the 90 and 180 degree pulses are perpendicular. However, only one slice can be excited during each repetition time, so multislice imaging is not possible. We present a modification of this method that allows multislice imaging. The slices excited by the 90 degrees and 180 degrees pulses are at a small angle; the field of view is limited and multislice imaging is possible. The modifications also allow the center of the FOV to be offset to any position. We describe the conditions that yield optimal images for the given FOV, slice thickness, and interslice gap. Representative images demonstrating the features of the technique are presented. The technique can be used to reduce the number of phase-encoding steps resulting in reduced imaging time, or it can be used to increase the spatial resolution without increasing the imaging time.     

Dual-echo breathhold T(2)-weighted fast spin echo MR imaging of liver lesions

The purpose of this study was to develop a multi-shot dual-echo breathhold fast spin echo technique (DFSE) and compare it with conventional spin echo (T2SE) for T(2)-weighted MR imaging of liver lesions. The DFSE acquisition (EffTE1/EffTE2/TR = 66/143/2100 ms) imaged 5 sections per 17 s breathhold. T2SE imaging (TE1/TE2/TR = 60/120/2500 ms) required 16:55 (min:s) for 14 sections. Both techniques used a receive-only phased-array abdominal multicoil and provided 192 x 256 effective resolution. The results showed first and second echo relative DFSE/T2SE contrast values for 27 representative lesions (15 consecutive patients) were 1.08 +/- 0.05 and 1.16 +/- 0.09 (mean +/- STD mean), respectively. Corresponding CNR values were 1.12 +/- 0.09 and 0.97 +/- 0.12. Overall DFSE was comparable-to-superior to T2SE for lesion sizing and image artifact. DFSE lesion detection was inferior to T2SE's in several patient studies because of decreased conspicuity of lesions located near multicoil edges and because of poor breathhold-to-breathhold reproducibility and lack of breathholding. However both DFSE (and T2SE) provided lesion detection rated to be of diagnostic quality for all patient studies. In conclusion, we found that DFSE provides diagnostically useful dual-echo T(2)-weighted MR liver images in a greatly decreased acquisition time.     

A prospective assessment of breath-hold fast spin echo and inversion recovery fast spin echo techniques for detection and characterization of focal hepatic lesions

The purpose of this study was to prospectively assess two breath-hold T(2)-weighted fast spin-echo sequences and two breath-hold inversion recovery fast spin-echo sequences to determine their relative ability to detect and characterize focal hepatic lesions. Fourteen patients with a total of nineteen proven focal hepatic lesions were imaged with two breath-hold T(2)-weighted (T2W) fast spin echo sequences (HASTE TE = 66 and HASTE TE = 120), two breath-hold inversion recovery fast spin echo sequences (IRFSE TE = 64 and IRFSE TE = 95), and a nonbreath-hold T(2)-weighted fast-spin echo sequence (FSE TE = 96-120). Contrast-to-noise ratios (CNRs) were measured for all proven lesions on all sequences. Both IRFSE sequences and the HASTE sequence with TE = 66 showed an improvement in lesion-liver and liver-spleen CNRs compared to the nonbreath-hold T2W sequence. The mean difference in CNR between benign and malignant lesions was largest for the HASTE TE = 120 sequence. These preliminary results suggest that a breath-hold IRFSE sequence (TE = 64 or 95) has an equal ability to detect focal hepatic lesions as a nonbreath-hold T2W FSE sequence (TE = 96-120). The HASTE TE = 120 showed the greatest ability to discriminate between benign and malignant lesions.     

Evaluation of the inner ear by 3D fast asymmetric spin echo (FASE) MR imaging: phantom and volunteer studies

The 3D fast asymmetric spin echo (FASE) method combines the half-Fourier technique and 3D fast spin echo (FSE) sequence. The advantage of this method is that it maintains the same spatial resolution as FSE while markedly reducing the imaging time. The purpose of the present study was to evaluate the usefulness of the 3D FASE technique in displaying the inner ear structure using phantom and volunteer studies. 3D FSE sequence images were obtained for comparison, and the optimum 3D FASE sequence was investigated on a 1.5T MR scanner. The results of phantom experiments showed increased signal-to-noise ratio (SNR) with prolonging repetition time (TR) on both 3D FASE and 3D FSE sequences. Although the SNR of 3D FASE images was 20-25% lower than that of 3D FSE images with the same TR, the SNR per minute with 3D FASE was about twice that with 3D FSE. On 3D FASE images, a higher spatial resolution was obtained with 2- or 4-shot images than with single-shot images. However, no significant difference was observed between 2-shot and 4-shot images. In the volunteer study, 3D FASE images using a TR of 5000 ms and an effective echo time (TEeff) of 250 ms showed a high SNR and spatial resolution and provided excellent contrast between cerebrospinal fluid and nerves in the internal auditory canal. The highest contrast was achieved in the 2-shot/2 number of excitations sequence. 3D FASE provides the same image quality as 3D FSE with a significant reducing in imaging time, and gives strong T2-weighted images. This method enables detailed visualization of the tiny structures of the inner ear.     

Diffusion-weighted imaging of the brain at 7 T with echo-planar and turbo spin echo sequences: preliminary results

Ultra-high-field clinical MRI scanners (e.g., 7 T and above) are becoming increasingly prevalent and can potentially enhance diagnostic ability through higher contrast, resolution and/or sensitivity. Diffusion-weighted MRI is a highly valued component in today's radiological exam and may benefit from the enhanced signal-to-noise ratio provided by high field with the appropriate imaging strategy. The most common diffusion pulse sequence readout (echo-planar imaging (EPI)) has been widely employed for in vivo human 7 T diffusion tensor imaging (DTI). In this article, we present results of brain DTI at 7 T with two diffusion-weighted imaging pulse sequence readouts: echo-planar imaging (EPI-DTI) and turbo spin echo (TSE-DTI). Results indicate that analogous coverage, quality and resolution typical of lower field (2 mm) can be obtained by properly processed EPI-DTI at 7 T, and, with some reduction in efficiency and sharpness, TSE-DTI at 7 T. Furthermore, 7 T TSE-DTI shows promise in obtaining higher-resolution results in targeted acquisitions of specific brain areas.     

Chorioangioma: antenatal diagnosis with fast MR imaging

We report a case of chorioangioma of the placenta, in which fast magnetic resonance imaging (MRI) was useful adjunct to ultrasonography for the antenatal diagnosis. MRI allowed clear demonstration of 6.8 x 6.0 cm solid placental mass along with hydramnios and anatomically normal fetus. On T(1)-weighted breath-hold spoiled gradient-echo (fast low-angle shot [FLASH]) images, chorioangioma was mostly isointense to the placenta, but had an area of high signal intensity near the base and at the periphery, suggestive of hemorrhage. On T(2)-weighted half-Fourier single-shot fast spin echo (HASTE) images, the mass showed heterogeneous high signal intensity, but had an area of low signal intensity near the surface.     

Dynamic half-Fourier single-shot turbo spin echo for assessment of deep venous thrombosis: initial observations

Objective

The objective of this study was to retrospectively analyze the value of dynamic half-Fourier single-shot turbo spin echo (HASTE) imaging in patients with suspected deep venous thrombosis (DVT).

Materials and Methods

Fifty-five veins in 24 patients were interrogated using a HASTE sequence with the patients relaxed and in various degrees of Valsalva. Veins were analyzed for changes in caliber (+CAL) and signal intensity (+SI) or in their absence (−CAL and −SI, respectively) and compared with the presence of thrombus on gadolinium-enhanced magnetic resonance imaging.

Results

There was no thrombus in veins with the +CAL, +SI pattern (n=40) (P<.01). Five of seven veins (71.4%) with the −CAL, −SI pattern had thrombus (P<.01). A qualitative change in CAL had a sensitivity of 100% and a specificity of 91% for the presence of thrombus. An increase of 1.5 mm in CAL had a sensitivity of 100% and a specificity of 93% for this diagnosis.

Conclusion

Dynamic HASTE imaging offers a physiological method to evaluate veins for deep venous thrombosis.     

Introduction of fast MR imaging in the assessment of hepatic steatosis

We determined the utility of fast gradient echo techniques (modified Dixon method) in the assessment of hepatic fat content. Fast spoiled gradient echo was performed on bovine liver/corn oil homogenates with known fat fractions (FF_E) to assess the accuracy of fat quantitation (FF_MRI). The pulse sequence was manipulated via alterations in TE (echo time), TR (repetition time), and α (flip angle). In vivo studies were then performed using breath-holding maneuvers on normal adult volunteers and subjects at risk to develop hepatic steatosis, with cystic fibrosis or morbid obesity. At out-of-phase, TE, TR, and α were 2.1 ms, 7.3 ms, and 30–50° and in-phase TE, TR, and α were 4.2 ms, 9.3 ms, and 30–50°; FF_MRI correlated well with FF_E. An elevated fat fraction was observed in a high percentage of subjects with cystic fibrosis and morbid obesity. Fast gradient echo techniques were used successfully in the assessment of hepatic steatosis. The reduced acquisition times permitted in vivo analysis on adults and children using breath hold maneuvers.     

Preoperative fast MRI of brain tumors using three-dimensional segmented echo planar imaging compared to three-dimensional gradient echo technique

The purpose of this study was to compare the diagnostic efficacy of a newly developed T(1)-weighted three-dimensional segmented echo planar imaging (3D EPI) sequence versus a conventional T(1)-weighted three dimensional spoiled gradient echo (3D GRE) sequence in the evaluation of brain tumors. Forty-four patients with cerebral tumors and infections were examined on a 1.0 T MR unit with 23 mT/m gradient strength. The total scan time for the T(1) 3D EPI sequence was 2 min 12 s, and for a conventional 3D GRE sequence it was 4 min 59 s. Both sequences were performed after administration of a contrast agent. The images were analyzed by three radiologists. Image assessment criteria included lesion conspicuity, contrast between different types of normal tissue, and image artifacts. In addition, signal-to-noise and contrast-to-noise-ratio (C/N) were calculated. The gray-white differentiation and C/N ratio of 3D EPI were found to be inferior to conventional 3D GRE images, but the difference was not statistically significant. In the qualitative comparison, lesion detection and conspicuity of 3D EPI images and conventional 3D GRE images were similar, but a tow-fold reduction of the scanning time was obtained. With the 3D EPI technique, a 50% scan time reduction could be achieved with acceptable image quality compared to conventional 3D GRE. Thus, the 3D EPI technique could replace conventional 3D GRE in the preoperative imaging of brain.     

Rapid acquisition of magnetic resonance imaging of the shoulder using three-dimensional fast spin echo sequence with compressed sensing

PurposeTo evaluate the feasibility of 3D fast spin-echo (FSE) imaging with compressed sensing (CS) for the assessment of shoulder.Materials and methodsTwenty-nine patients who underwent shoulder MRI including image sets of axial 3D-FSE sequence without CS and with CS, using an acceleration factor of 1.5, were included. Quantitative assessment was performed by calculating the root mean square error (RMSE) and structural similarity index (SSIM). Two musculoskeletal radiologists compared image quality of 3D-FSE sequences without CS and with CS, and scored the qualitative agreement between sequences, using a five-point scale. Diagnostic agreement for pathologic shoulder lesions between the two sequences was evaluated.ResultsThe acquisition time of 3D-FSE MRI was reduced using CS (3 min 23 s vs. 2 min 22 s). Quantitative evaluations showed a significant correlation between the two sequences (r = 0.872–0.993, p < 0.05) and SSIM was in an acceptable range (0.940–0.993; mean ± standard deviation, 0.968 ± 0.018). Qualitative image quality showed good to excellent agreement between 3D-FSE images without CS and with CS. Diagnostic agreement for pathologic shoulder lesions between the two sequences was very good (κ = 0.915–1).ConclusionsThe 3D-FSE sequence with CS is feasible in evaluating the shoulder joint with reduced scan time compared to 3D-FSE without CS.     

A fast spin echo two-point Dixon technique and its combination with sensitivity encoding for efficient T2-weighted imaging

A fast spin echo two-point Dixon (fast 2PD) technique was developed for efficient T2-weighted imaging with uniform water and fat separation. The technique acquires two interleaved fast spin echo images with water and fat in-phase and 180° out-of-phase, respectively, and generates automatically separate water and fat images for each slice. The image reconstruction algorithm uses an improved and robust region-growing scheme for phase correction and achieves consistency in water and fat identification between different slices by exploiting the intrinsic correlation between the complex images from two neighboring slices. To further lower the acquisition time to that of a regular fast spin echo acquisition with a single signal average, we combined the fast 2PD technique with sensitivity encoding (SENSE). Phantom experiments show that the fast 2PD and SENSE are complementary in scan efficiency and signal-to-noise ratio (SNR). In vivo data from scanning of clinical patients demonstrate that T2-weighted imaging with uniform and consistent fat separation, including breath-hold abdominal examinations, can be readily performed with the fast 2PD technique or its combination with SENSE.     

Microscopic imaging of slow flow and diffusion: a pulsed field gradient stimulated echo sequence combined with turbo spin echo imaging.

In this paper we present a pulse sequence that combines a displacement-encoded stimulated echo with rapid sampling of k-space by means of turbo spin echo imaging. The stimulated echo enables the use of long observation times between the two pulsed field gradients that sample q-space completely. Propagators, constructed with long observation times, could discriminate slowly flowing protons from diffusing protons, as shown in a phantom in which a plug flow with linear velocity of 50microm/s could clearly be distinguished from stationary water. As a biological application the apparent diffusion constant in longitudinal direction of a transverse image of a maize plant stem had been measured as a function of observation time. Increasing contrast in the apparent diffusion constant image with increasing observation times were caused by differences in plant tissue: although the plant stem did not take up any water, the vascular bundles, concentrated in the outer ring of the stem, could still be discerned because of their longer unrestricted diffusional pathways for water in the longitudinal direction compared to cells in the parenchymal tissue. In the xylem region of a tomato pedicel flowing water could be distinguished from a large amount of stationary water. Linear flow velocities up to 0.67 mm/s were measured with an observation time of 180 ms.     

Diffusion-weighted imaging in the prostate: an apparent diffusion coefficient comparison of half-Fourier acquisition single-shot turbo spin-echo and echo planar imaging

Prostate cancer detection using diffusion-weighted imaging is highly affected by the accuracy of the apparent diffusion coefficient (ADC) values in an image. Echo planar imaging (EPI) is a fast sequence commonly used for diffusion imaging but has inherent magnetic susceptibility and chemical shift artefacts associated. A diffusion sequence that is less affected by these artefacts is therefore advantageous. The half-Fourier acquisition single-shot turbo spin-echo (HASTE) sequence was chosen. The diffusion sequences were compared in image quality, repeatability of the ADC value and the effect on the ADC value with varied b values. Eight volunteers underwent three scans of each sequence, on a 1.5-T Siemens system, using b values of 0, 150, 300, 450, 600, 750, 900 and 1000 s/mm(2). ADC maps were created to address the reproducibility of the ADC value when using two b values compared to eight b values. The ADC value using all b values with the HASTE sequence gave the best performance in all tested categories. Both sequences gave significantly different ADC mean values for two b values compared to when using eight b values (P<.05) suggesting larger error is present when using two b values. HASTE was shown to be an improvement over EPI in terms of repeatability, signal variation within a region of interest and standard deviation over the volunteer set. The improved accuracy of the ADC value in the HASTE sequence makes it potentially a more sensitive tumor detection technique.