Conventional and fast spin-echo MR imaging: minimizing echo time

Rapid variable flip angle positive susceptibility contrast imaging for clinical metal seeds

Positive susceptibility contrast imaging (PSCI) based on susceptibility mapping exhibits excellent efficacy for visualizing magnetic resonance (MR)-compatible metallic devices because of their high magnetic susceptibility compared to that of human tissues. However, the long-acquisition time required by the two-dimensional fast spin echo (2D FSE)-based PSCI approach, impedes its practical applications in 3D imaging. In this study, a three-dimensional (3D) susceptibility-based variable flip angle (vFA) FSE sequence was proposed to accelerate data acquisition in the clinical radiotherapy applications of ex vivo and in vivo rapid 3D PSCI for the imaging of metal seeds. Here, the proposed scheme applied a 3D modulated vFA technique for refocused imaging with an extended echo-train sequence for sampling data. The scheme integrated the projection-onto-dipole fields (PDF) to remove the background field and accelerate PSCI by using a compressive sensing framework with a variable-densitysampling mask. The experiments involved some gelatin phantoms, porcine tissues and patients with scapular tumors and brachytherapy seeds. All of the experimental results showed that the proposed scheme could accelerate data acquisition of 3D PSCI at the reduction factors of 2 ∼ 5 while accurately localizing the actual positions of the brachytherapy seeds in the ex vivo and in vivo applications. The results were compared with those of the existing methods, including susceptibility gradient mapping using the original resolution (SUMO) and gradient echo acquisition for superparamagnetic particle (GRASP).

Three-dimensional quantification of magnetic resonance imaging artifacts associated with shape factors

Differences in the volumes of artifacts caused by variously shaped titanium objects on magnetic resonance imaging (MRI) were evaluated. Spherical-, square cubic-, and regular tetrahedron-shaped isotropic, and elongated spherical-, elongated cubic-, and elongated tetrahedron-shaped anisotropic objects, with identical volumes, were prepared. Samples were placed on a nickel-doped agarose gel phantom and covered with nickel-nitrate hexahydrate solution. Three-Tesla MR images were obtained using turbo spin echo and gradient echo sequences. Areas with ±30% of the signal intensity of the standard background value were considered artifacts. Sample volumes were deducted from these volumes to calculate the total artifact volumes. Isotropic samples had similar artifact volumes. For anisotropic samples, the artifact volume increased in proportion with the normalized projection area. MRI artifact size can be reduced by high anisotropic designs, and by positioning the long axis of the metal device as parallel as possible to the magnetic field axis.

Quantitative Versus Qualitative Methods in Evaluation of T2 Signal Intensity to Improve Accuracy in Diagnosis of Pheochromocytoma

OBJECTIVE

The purpose of this study was to assess T2 signal intensity (SI) of adrenal pheochromocytoma at 1.5 T using the rapid acquisitions with relaxation enhancement (RARE) sequence. We also sought to determine whether quantitative parameters can distinguish pheochromocytoma from other adrenal lesions with better accuracy than conventional qualitative methods.

MATERIALS AND METHODS

MRI examinations of 74 patients (26 with pheochromocytoma, 25 with lipid-poor adenomas, 18 with malignant adrenal lesions, and five with adrenal cysts) were retrospectively reviewed. MRI sequences included single-shot fast spin-echo (n = 38) and fast-recovery fast spin-echo (n = 36) acquisitions. T2 SI of lesions was qualitatively compared with CSF. Quantitative evaluation included applying ROI measurements and calculating SI ratio of each mass to liver, spleen, paraspinal muscle, and CSF. Twoway ANOVA compared SI ratios between different adrenal lesions and between two pulse sequences. ROC analysis determined the optimal threshold SI ratio for distinguishing pheochromocytomas from other adrenal lesions.

RESULTS

Sixty-nine percent of pheochromocytomas displayed isointensity to CSF (p < 0.005), resulting in 81% specificity and 69% sensitivity for differentiation of pheochromocytomas from lipid-poor adenomas and malignant lesions. Adrenal-to-muscle SI ratio was the strongest discriminator for differentiation of pheochromocytomas from other lesions. A threshold of at least 3.95 yielded 88% specificity and 81% sensitivity for distinguishing pheochromocytomas from lipid-poor adenomas and malignant adrenal lesions.

CONCLUSION

Quantitative normalization of T2 SI with reference to muscle improves the sensitivity and specificity profile for differentiation of pheochromocytoma compared with qualitative assessment alone. At 1.5 T field strength, an adrenal-to-muscle SI ratio of at least 3.95 is recommended.

Evaluation of pneumonia in children: comparison of MRI with fast imaging sequences at 1.5T with chest radiographs

BACKGROUND

Although there has been a study aimed at magnetic resonance imaging (MRI) evaluation of pneumonia in children at a low magnetic field (0.2T), there is no study which assessed the efficacy of MRI, particularly with fast imaging sequences at 1.5T, for evaluating pneumonia in children.

PURPOSE

To investigate the efficacy of chest MRI with fast imaging sequences at 1.5T for evaluating pneumonia in children by comparing MRI findings with those of chest radiographs.

MATERIAL AND METHODS

This was an Institutional Review Board-approved, HIPPA-compliant prospective study of 40 consecutive pediatric patients (24 boys, 16 girls; mean age 7.3 years ± 6.6 years) with pneumonia, who underwent PA and lateral chest radiographs followed by MRI within 24 h. All MRI studies were obtained in axial and coronal planes with two different fast imaging sequences: T1-weighted FFE (Fast Field Echo) (TR/TE: 83/4.6) and T2-weigthed B-FFE M2D (Balanced Fast Field Echo Multiple 2D Dimensional) (TR/TE: 3.2/1.6). Two experienced pediatric radiologists reviewed each chest radiograph and MRI for the presence of consolidation, necrosis/abscess, bronchiectasis, and pleural effusion. Chest radiograph and MRI findings were compared with Kappa statistics.

RESULTS

All consolidation, lung necrosis/abscess, bronchiectasis, and pleural effusion detected with chest radiographs were also detected with MRI. There was statistically substantial agreement between chest radiographs and MRI in detecting consolidation (k = 0.78) and bronchiectasis (k = 0.72) in children with pneumonia. The agreement between chest radiographs and MRI was moderate for detecting necrosis/abscess (k = 0.49) and fair for detecting pleural effusion (k = 0.30).

CONCLUSION

MRI with fast imaging sequences is comparable to chest radiographs for evaluating underlying pulmonary consolidation, bronchiectasis, necrosis/abscess, and pleural effusion often associated with pneumonia in children.

Multishot PROPELLER for high-field preclinical MRI

With the development of numerous mouse models of cancer, there is a tremendous need for an appropriate imaging technique to study the disease evolution. High-field T(2)-weighted imaging using PROPELLER (Periodically Rotated Overlapping ParallEL Lines with Enhanced Reconstruction) MRI meets this need. The two-shot PROPELLER technique presented here provides (a) high spatial resolution, (b) high contrast resolution, and (c) rapid and noninvasive imaging, which enables high-throughput, longitudinal studies in free-breathing mice. Unique data collection and reconstruction makes this method robust against motion artifacts. The two-shot modification introduced here retains more high-frequency information and provides higher signal-to-noise ratio than conventional single-shot PROPELLER, making this sequence feasible at high fields, where signal loss is rapid. Results are shown in a liver metastases model to demonstrate the utility of this technique in one of the more challenging regions of the mouse, which is the abdomen.

Improved delineation of ventricular shunt catheters using fast steady-state gradient recalled-echo sequences in a rapid brain MR imaging protocol in nonsedated pediatric patients

BACKGROUND AND PURPOSE

Rapid brain MR imaging is often substituted for head CT in multiply imaged patients with shunted hydrocephalus. Fast TSE-T2 sequences are commonly used in these protocols. One limitation of TSE-T2 sequences is the decreased catheter delineation compared with CT. The aim of this study was to compare fast TSE-T2 with rapid SS-GRE sequences in the evaluation of intracranial shunt catheter delineation as part of a rapid nonsedated pediatric brain MR imaging protocol.

MATERIALS AND METHODS

We evaluated the findings from 179 consecutive patients who underwent routine clinical imaging according to the rapid nonsedated pediatric brain MR imaging protocol. Comparison of the quality of intracranial shunt catheter localization on SS-GRE versus TSE-T2 was performed.

RESULTS

Of the total of 179 rapid nonsedated pediatric brain MR images that were reviewed, 62 (35%) had an intracranial shunt catheter. The shunt catheter tip was better localized on the SS-GRE than on the TSE-T2 images in 49/62 (79%) of these patients. Of the remaining 13/62 (21%), the TSE-T2 was either better or equivalent in localizing the shunt catheter tip.

CONCLUSIONS

Our study shows that rapid SS-GRE sequences can provide better delineation of standard intracranial shunt catheters than standard rapid MR imaging protocols containing only fast TSE-T2 sequences.

[Postoperative syndrome after spine surgery]

Postoperative syndrome after spine surgery, i.e., symptoms or syndromes caused by complications or procedure-related consequences, is gaining more and more importance. Due to great improvements concerning imaging and operative techniques (microsurgery, instrumentation) the total number of spinal surgeries as well as their related complications are increasing. Procedure-related postoperative complications including neurological deficit syndromes can occur acutely or at a later date. Concerning imaging techniques for postoperative evaluation after spinal surgery there are several modalities available. Their indications depend on complex factors including initial pathology the surgery was performed for, kind of surgical technique (surgical approach, instrumentation), anatomy of the patient as well as the time between onset of symptoms and surgery. In cases of ambiguous findings, the combination of different imaging techniques can be instrumental.

Metal artifact reduction in musculoskeletal magnetic resonance imaging

Many strategies can be employed to reduce the size and scale of metal susceptibility artifacts in the vicinity of orthopedic hardware; factors include selection of metal hardware material, patient positioning, and MRI sequence adjustments and techniques. The adjustments to sequence parameters include high spatial resolution fast spin echo sequences with minimal interecho spacing and increased receiver bandwidth. Frequency and phase encoding gradients can be orientated so misregistration artifacts arising from the metal are directed away from areas of anticipated clinical diagnostic interest. Complications arising in the vicinity of metallic hardware, including loosening, can be assessed after implication of these metal artifact reduction techniques.

Quantification and minimization of magnetic susceptibility artifacts on GRE images

PURPOSE

The purpose of this work was to determine the optimal imaging parameters for minimization of metallic susceptibility artifacts during gradient echo (GRE) imaging.

METHOD

We performed GRE imaging of titanium screws in a nickel-doped agarose gel phantom, systematically varying several parameters to characterize and quantify susceptibility artifacts.

RESULTS

The greatest reduction in artifact size came from using a short TE; increasing the frequency matrix and decreasing the slice thickness also contributed substantially to reducing the artifact size. Whenever possible, implanted prostheses should be aligned with the main magnetic field to minimize artifact size. Parameters with negligible effect on artifact size included bandwidth, phase encode matrix, and field of view.

CONCLUSION

Radiologists can easily adjust the above parameters in their imaging protocols to improve GRE image quality in patients with implanted metallic devices.

Experimental study on HASTE sequences: impacts of parameters on liver imaging

This study investigates the impacts of effective TE (TEeff), echo spacing and echo train lengths (ETLs) on the imaging quality of HASTE sequences for liver imaging through a slit and a liver phantom. The HASTE sequence with a short echo spacing demonstrated higher CNR for a phantom simulating hepatocellular carcinoma (HCC) than that with long echo spacing. With a long echo spacing, the HASTE sequence showed higher spatial resolution for hemangiomas and metastasis. The improvement of spatial resolution along with the increase in ETLs (imaging matrix) was more prominent for hemangioma than for HCC.

Differentiation of hepatic cavernous hemangioma from metastases by rare sequence MR imaging

In this study, in order to differentiate cavernous hemangioma and hepatic metastases, rapid acquisition relaxation enhanced (RARE) sequence was used. First, in vivo measurements of T1, T2 relaxation times and proton density were obtained using T1, T2 calculation protocol (TOMIKON S50, 0.5T) and multipoint techniques. These measurements were made from regions of interest placed over the liver, spleen (because of similarity of relaxation time values between hepatic metastases and spleen) and cavernous hemangioma (HCH). Based on these intrinsic parameters, T2 curves signal intensity of three different tissues were constructed. At TE = 500 ms, the signal intensity of the liver and spleen has been near zero whereas in HCH, the signal intensity remained. As RARE sequence is very similar to spin echo (SE), by replacing effective TE(ETE) = 500 ms in the RARE equation, two dimensional contrast-to-noise ratio (CNR) contour plots were constructed demonstrating signal intensity contrast between liver-spleen, liver-Hemangioma for two different scan times (3 min, 7.5 s) and pulse timing. Then, optimal RARE factor and inter echo times were obtained in order to have maximum CNR between liver-Hemangioma and minimum CNR between liver-spleen. These optimal parameters were performed on ten normal and five persons with known HCH. Images showed that in both scan times (3 min, 7.5 s); the liver and spleen were suppressed whereas the HCH was enhanced. The image quality in the scan time of 3 min was better than the scan time of 7.5 s. Moreover, in this study, two different sequences were compared: i) Multi-slice single echo (MSSE) for T1 weighted image ii) RARE (ETE = 80 ms) for T2-weighted image. This comparison was done to show maximum CNR between liver-spleen (metastases) and to choose a better sequence for detecting metastases. CNR in the RARE sequence was more than in the MSSE sequence.

Ultrafast MR imaging of the pelvis

MR gradient systems with higher slew rates and gradient amplitude enable certain forms of imaging that are not practical with older gradient systems. These newer pulse sequences include single shot half-Fourier T2-weighted images and echo planar imaging. More important in MR imaging of the pelvis, these gradient systems benefit more conventional imaging methods such as gadolinium-enhanced 3D MR angiography, dynamic gradient echo contrast-enhanced images, and T2-weighted fast spin echo images, by shortening echo times. For most MR imaging of the pelvis, spatial resolution is paramount, and therefore sequences such as half-Fourier acquisition Turbo spin echo (HASTE) and 3D gadolinium-enhanced dynamic imaging play a less important role than in the upper abdomen. The potential of these techniques for diffusion or perfusion studies in the pelvis has not been explored.

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.

Fast magnetic resonance imaging of the lung

The impact of fast MR techniques developed for MR imaging of the lung will soon be recognized as equivalent to the high-resolution technique in chest CT imaging. In this article, the difficulties in MR imaging posed by lung morphology and its physiological motion are briefly introduced. Then, fast MR imaging techniques to overcome the problems of lung imaging and recent applications of the fast MR techniques including pulmonary perfusion and ventilation imaging are discussed. Fast MR imaging opens a new exciting window to multi-functional MR imaging of the lung. We believe that fast MR functional imaging will play an important role in the assessment of pulmonary function and disease process.

Minimizing artifacts caused by metallic implants at MR imaging: experimental and clinical studies

OBJECTIVE

The purpose of this study was to investigate the effect of metallic implant positioning on MR imaging artifacts, to determine the optimal imaging conditions for minimizing artifacts, and to show the usefulness of artifact-minimizing methods in imaging of the knee.

MATERIALS AND METHODS

Using MR images of experimental phantoms (titanium alloy and stainless steel screws), we compared the magnitude of metal-induced artifacts for various pulse sequences, different imaging parameters for the fast spin-echo sequence, and different imaging parameters for several incremental angles between the long axis of the screw and the direction of the main magnetic field. In clinical MR imaging of knees with metallic implants (n = 19), we assessed geometric distortion of anatomic structures to compare the influence of different pulse sequences (n = 19), frequency-encoding directions (n = 7), and knee positions (n = 15).

RESULTS

Titanium alloy screws consistently produced smaller artifacts than did stainless steel screws. In experimental MR studies, artifacts were reduced with fast spin-echo sequences, with a screw orientation as closely parallel to the main magnetic field as possible, and, particularly, with smaller voxels that correlated positively with artifact size (R2 = .88, p < .01). In clinical MR studies, fast spin-echo MR imaging obscured articular structures less than did spin-echo imaging (8/19 patients). In particular, the anterior-posterior frequency-encoding direction (3/7 patients) and the flexion position of the knee (5/15 patients) were effective in reducing artifacts.

CONCLUSION

MR artifacts can be minimized by optimally positioning in the magnet subjects with metallic implants and by choosing fast spin-echo sequences with an anterior-posterior frequency-encoding direction and the smallest voxel size.

Advances in pediatric neuroimaging

Magnetic resonance evaluation of the pediatric central nervous system is rapidly improving in a number of ways: (1) anatomically with higher resolution; (2) with greater sensitivity to pathological processes characterized by increased water content utilizing fluid attenuated inversion recovery imaging (FLAIR); (3) with greater speed of acquisition with ultrafast (1 s/image) and echo planar imaging techniques (50 ms/image); (4) with measurement of cerebral blood flow as perfusion; (5) with measurement of water proton dispersion (e.g. diffusion imaging); (6) with measurement of biochemical components within tissues with proton spectroscopy; and (7) with evaluation of cortical activation with functional magnetic resonance imaging.

Hepatic T2-weighted MRI: a prospective comparison of sequences, including breath-hold, half-Fourier turbo spin echo (HASTE)

The purpose of this study was to quantitatively compare the hepatic contrast characteristics of conventional spin-echo (CSE) and fast spin-echo (FSE) sequences with breath-hold T2-weighted images acquired with half-Fourier turbo spin echo (HASTE). Forty-five patients were examined with a phased-array surface coil. Nineteen patients had focal hepatic lesions, including eight malignant tumors, 10 cavernous hemangiomas, and one hepatic adenoma. Twenty-six patients had no focal hepatic lesions. T2-weighted images with comparable TE were acquired with CSE, FSE, and HASTE pulse sequences. Signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR) for liver, spleen, and lesions were measured. FSE demonstrated significantly better quantitative performance than CSE for liver-spleen CNR (P .0084). No statistically significant difference was demonstrated between FSE and CSE for liver or spleen SNR. FSE demonstrated clear scan time and resolution advantages over CSE. HASTE performed significantly poorer than CSE and FSE for liver-spleen CNR (P < .0001), liver SNR (P = .0002 for CSE and P < .0001 for FSE), and spleen SNR (P < .0001). Optimized FSE images with a short echo train length performed comparably to CSE images of equivalent TE. Liver-lesion CNR was suppressed on HASTE images, suggesting that long echo train length FSE sequences could diminish solid lesion detection compared to CSE and short echo train length FSE.

Ultrafast T2-weighted imaging of the abdomen and pelvis: use of single shot fast spin-echo imaging

Single shot (SS) rapid acquisition with relaxation enhancement (RARE) and half Fourier SS-RARE (HFSS-RARE, HASTE, or SS-FSE) sequences allow ultrafast imaging acquisition and generate high imaging quality. Images can be acquired within a very short time, without artifacts from physiologic motion. They are widely applied in the abdominal MRI. Clinical application of the ultrafast SS-RARE imaging techniques provide not only improved temporal resolution but better spatial resolution, higher SNR, and higher tissue contrast. Imaging parameters must be optimized for different MR scanners to obtain diagnostic images.

Imaging orthopedic hardware with an emphasis on hip prostheses

This article reviews contemporary evaluation of hip prostheses, emphasizing both the accepted use of conventional radiographs, arthrograms, and scintigraphy, as well as the evolving use of CT and MR imaging in evaluating suspected complications. Developments in CT postprocessing and MR pulse sequence design now allow successful imaging of soft tissues adjacent to hardware components.

MR pulmonary angiography and perfusion imaging: recent advances

Recent advances in MR pulmonary angiography and MR perfusion imaging are reviewed, focusing on two principal areas of technical development: (1) the availability of MR scanners equipped with enhanced gradient systems; and (2) new trends in MR angiography using gadolinium contrast agents or labeling of blood with an inversion recovery radiofrequency pulse in place of the more traditional methods using naturally flowing spins as the source of intravascular signal. These recent developments in MR have significant potential for clinical imaging of the pulmonary vasculature, particularly for the diagnosis of pulmonary embolism, and are now opening windows to functional MR imaging of the lung.

Evaluation of the temporal evolution of acute spinal cord injury

RATIONALE AND OBJECTIVES

After receiving a controlled injury to the thoracic cord, five rats were examined on a 1.5-T magnetic resonance (MR) imaging system at regular intervals over 1 month to assess evolution of the injury.

METHODS

After the rats received pentobarbital anesthesia, a T10 laminectomy was performed on them, which exposed the dura over the dorsal surface of the spinal cord. With the animal placed in a New York University weight-drop device, a 10-g rod with a flat brass tip was dropped (free-fall) from a height of 50 mm to impact the cord. After injury, the incision was closed with suture material. Each animal was imaged on the day of injury, and at 7, 14, and 28 days after injury. Before contrast injection was administered, sagittal sections were obtained with T2 fast-spin echo and T1-spin echo technique. Each rat then received 0.3-mmol/kg gadoteridol (Gd HP-DO3A or ProHance) intravenously, with the T1 scan repeated. At 28 days, the animals were killed, and the cord was fixed and embedded in paraffin for histologic evaluation.

RESULTS

The intensity of cord enhancement in the region of injury, after intravenous (i.v.) contrast injection, was at a maximum on the day of injury, and it decreased in a steady fashion thereafter. The intensity was 11.7 +/- 0.6 on the day of injury, 9.7 +/- 2.6 on day 7, 6.3 +/- 5.3 on day 14, and 0.0 +/- 2.3 on day 28. The results on day 0 and 7 were statistically significant in terms of a difference from that on day 28, with a P value < 0.001. The length of cord injury, assessed postcontrast, also decreased in a steady fashion from the day of injury. The length of injury (in cm) was 1.1 +/- 0.1 on the day of injury, 0.5 +/- 0.2 on day 7, 0.3 +/- 0.1 on day 14, and 0.1 +/- 0.1 on day 28. The results on day 0 and 14 were statistically significant in terms of a difference from those at the next time point, with P values from < 0.01 to < 0.001. Visually, on T2 images, substantial edema was noted on day 0, with progression to focal cord atrophy and gliosis by day 28.

CONCLUSIONS

Acute spinal cord injury in a rat model is well visualized on pre- and postcontrast MR scans at 1.5 T. Observation of T2 changes and disruption of the blood-spinal cord barrier provide markers for temporal assessment of spinal cord injury in the rat model.

Comparison between magnetization transfer contrast and fast spin-echo MR imaging of degenerative disease of the cervical spine at 0.3 T

We compared magnetization transfer contrast (MTC) with gradient recalled echo (GRE) magnetic resonance imaging (MRI) and fast spin-echo (FSE) MRI of the degenerative cervical spine at 0.3 T. Fifty patients with suspected degenerative disease of the cervical spine were prospectively evaluated. Multislice sagittal and axial images of the cervical spine were obtained using MTC GRE sequence [repetition time (TR)/echo time (TE)/flip angle = 750/23/25 degrees] and FSE sequence with peripheral gating (TR/effective TE = 2000-4000/120). Quantitatively, FSE showed higher signal-to-noise ratio and superior disk contrast between normal and degenerative disks, while MTC images showed superior contrast-to-noise ratio for the cerebrospinal fluid (CSF) versus cord and superior CSF homogeneity. In qualitative analysis, similar results were obtained. In conclusion, FSE and MTC GRE sequences are MRI techniques of imaging the cervical spine that have different characteristics and supplement each other in the diagnostic imaging of degenerative disease of the cervical spine.

The role of T2-weighted fast-spin-echo imaging in the diagnosis of meniscal tears

The objective of this study was to compare the accuracy of T2-weighted fast-spin-echo (FSE) and intermediate-weighted spin-echo (SE) MR imaging in the detection of meniscal tears. Seventy-six patients (152 menisci) who had arthroscopic surgery after MR imaging of the knee were studied. MR imaging included intermediate-weighted SE and T2-weighted FSE sequences. The use of intermediate-weighted conventional SE images, T2-weighted FSE images, and a combination of both sequences were evaluated in the detection of meniscal tears. T2-weighted FSE imaging was slightly less accurate than intermediate-weighted SE imaging in the diagnosis of meniscal tears. Interpretation of the menisci using both intermediate-weighted SE and T2-weighted FSE imaging did not improve the accuracy over intermediate-weighted imaging evaluated in isolation.

Delineation of pancreas with MR imaging: multiobserver comparison of five pulse sequences

The authors compared five magnetic resonance (MR) imaging pulse sequences for their ability to depict the pancreas in 59 patients, each evaluated with at least two of the five sequences. Focal pancreatic carcinomas were present in eight patients. The five sequences were T1-weighted spin echo (T1-SE), fat-suppressed T1-SE (T1-FS), T1-weighted gradient echo (T1-GRE), T2-weighted SE (T2-SE), and T2-weighted fast spin echo (T2-FSE). Using repeated-measures analysis, three blinded observers independently reviewed 198 separate MR imaging series and rated them on a 5-point scale with regard to image quality and depiction of pancreatic borders and the number of sections containing pancreatic and common bile ducts. The most superior and most inferior sections containing pancreas were recorded for each sequence in each patient. The results were compared with analysis of variance, and interobserver agreement was measured with the intraclass correlation coefficient (ICC). For image quality, all sequences were rated good to excellent, with the T1-SE sequence having the highest rating. For clarity of pancreatic borders, however, the T1-FS sequence was rated significantly higher (P < .006) than the other sequences; the T2-SE sequence was least satisfactory. Common bile and pancreatic ducts were seen in the most sections with the T2-FSE sequence. There were no significant differences regarding identification of the most superior and inferior sections containing pancreas, and the ICC was high (.91-.97) for all sequences. For detecting focal carcinomas, no single pulse sequence was sufficient.

Fast spin-echo MR imaging of the abdomen: contrast optimization and artifact reduction

The effects of various fast spin-echo (FSE) magnetic resonance (MR) imaging parameters and artifact reduction techniques on FSE image contrast and quality were studied. The authors performed 139 abdominal MR examinations, comparing standard FSE images (echo train length [ETL] = 8, echo space [E-space] = 17 msec, bandwidth = +/- 16-kHz) with FSE images with an ETL of 16 (n = 22) or FSE images with a +/- 32-kHz bandwidth and an E-space of 11-14 msec (n = 22). FSE artifact reduction techniques were evaluated with spectral fat saturation (n = 40) or with a new flow compensation FSE sequence (n = 55). Images of liver lesions were reviewed qualitatively and with contrast-to-noise ratio (C/N) measurements. Decreasing the time of echo train sampling produced superior image quality, with increased anatomic sharpness, less image artifact, and improved liver-lesion C/N. Images obtained with an ETL of 16 showed more image blurring and a 23% decrease in relative contrast and 28% decrease in relative C/N for liver tumors. Increasing the bandwidth reduced E-space, producing a 12% decrease in background noise. Artifact reduction with fat saturation or flow compensation produced images with less ghosting artifact and superior overall image quality, with 39% and 20% increases in liver-tumor C/N, respectively. FSE image quality and contrast in the depiction of hepatic disease can be optimized with careful selection of imaging parameters and the use of artifact reduction techniques.

Hybrid RARE: implementations for abdominal MR imaging

Hybrid RARE (rapid acquisition with relaxation enhancement) is a family of magnetic resonance (MR) imaging techniques whereby a set of images is phase encoded with more than one spin echo per excitation pulse. This increases the efficiency of obtaining T2-weighted images, allowing greater flexibility regarding acquisition time, resolution, signal-to-noise ratio, and tissue contrast. Hybrid RARE techniques involve several important new user-selectable parameters such as effective TE, echo train length, and echo spacing. Choices of other parameters, such as TR, sampling bandwidth, and acquisition matrix, may be different from those of comparable conventional T2-weighted spin-echo images. Different hybrid RARE implementations can be used for abdominal screening, with T2-weighted or T2-weighted and inversion-recovery contrast, or for characterizing liver lesions or imaging the biliary system with an extremely long TE. High-resolution images may be obtained by averaging multiple signals during quiet breathing, or images may be acquired more rapidly during suspended respiration. In this review, the authors discuss the basic principles of hybrid RARE techniques and how various imaging parameters can be manipulated to increase the quality and flexibility of abdominal T2-weighted MR imaging.