T-1 weighted sequences for hepatic MRI: re-evaluation using a phased array coil.

The purpose of this study was to compare three T1-weighted sequences for hepatic magnetic resonance (MRI) imaging with the use of a body phased array coil. Three different T1-weighted MR sequences were compared: a conventional spin echo (CSE); half-Fourier spin echo (HFSE), and a gradient recalled echo (GRE). Three independent reviewers compared the sequences both quantitatively and qualitatively. The T1-weighted GRE sequence scored highest for overall image quality (p < 0.001), lesion conspicuity (p = 0.012), and yielded the highest contrast to noise (C/N) values. GRE T1-weighted images are the best for hepatic MRI.     

High-resolution magnetic resonance imaging of the anal sphincter using a dedicated endoanal receiver coil

The use of a surface coil in MR imaging improves signal-to-noise ratio of adjacent tissues of interest. We therefore devised an endoanal receiver coil for imaging the anal sphincter. The probe is solid and re-usable: it comprises a saddle geometry receiver with integral tuning, matching and decoupling. It is placed in the anal canal and immobilised externally. Both in vitro and in vivo normal anatomy is identified. The mucosa is high signal intensity, the submucosa low signal intensity, the internal sphincter uniformly high signal intensity and the external sphincter low signal intensity on T1- and T2-weighted images. In females, the transverse perineal muscle bridges the inferior part of the external sphincter anteriorly. In perianal sepsis, collections and the site of the endoanal opening are identified. In early-onset fecal incontinence following obstetric trauma/surgery, focal sphincter defects are demonstrated; in late-onset fecal incontinence external sphincter atrophy is seen. In fecally incontinent patients with scleroderma, forward deviation of the anterior sphincter musculature with descent of rectal air and feces into the anal canal is noted. The extent of sphincter invasion is assessed in low rectal tumours. In children with congenital anorectal anomalies, abnormalities of the muscle components are defined using smaller-diameter coils. Such information is invaluable in the assessment and surgical planning of patients with a variety of anorectal pathologies. Received: 17 March 1998; Revision received: 19 May 1998; Accepted: 27 May 1998     

3.0 Tesla high spatial resolution contrast-enhanced magnetic resonance angiography (CE-MRA) of the pulmonary circulation: initial experience with a 32-channel phased array coil using a high relaxivity contrast agent

PURPOSE: To evaluate the technical feasibility of high spatial resolution contrast-enhanced magnetic resonance angiography (CE-MRA) with highly accelerated parallel acquisition at 3.0 T using a 32-channel phased array coil, and a high relaxivity contrast agent. MATERIALS AND METHODS: Ten adult healthy volunteers (5 men, 5 women, aged 21-66 years) underwent high spatial resolution CE-MRA of the pulmonary circulation. Imaging was performed at 3 T using a 32-channel phase array coil. After intravenous injection of 1 mL of gadobenate dimeglumine (Gd-BOPTA) at 1.5 mL/s, a timing bolus was used to measure the transit time from the arm vein to the main pulmonary artery. Subsequently following intravenous injection of 0.1 mmol/kg of Gd-BOPTA at the same rate, isotropic high spatial resolution data sets (1 x 1 x 1 mm3) CE-MRA of the entire pulmonary circulation were acquired using a fast gradient-recalled echo sequence (TR/TE 3/1.2 milliseconds, FA 18 degrees) and highly accelerated parallel acquisition (GRAPPA x 6) during a 20-second breath hold. The presence of artifact, noise, and image quality of the pulmonary arterial segments were evaluated independently by 2 radiologists. Phantom measurements were performed to assess the signal-to-noise ratio (SNR). Statistical analysis of data was performed by using Wilcoxon rank sum test and 2-sample Student t test. The interobserver variability was tested by kappa coefficient. RESULTS: All studies were of diagnostic quality as determined by both observers. The pulmonary arteries were routinely identified up to fifth-order branches, with definition in the diagnostic range and excellent interobserver agreement (kappa = 0.84, 95% confidence interval 0.77-0.90). Phantom measurements showed significantly lower SNR (P < 0.01) using GRAPPA (17.3 +/- 18.8) compared with measurements without parallel acquisition (58 +/- 49.4). CONCLUSION: The described 3 T CE-MRA protocol in addition to high T1 relaxivity of Gd-BOPTA provides sufficient SNR to support highly accelerated parallel acquisition (GRAPPA x 6), resulting in acquisition of isotopic (1 x 1 x 1 mm3) voxels over the entire pulmonary circulation in 20 seconds.     

Ultrasound imaging of the anal sphincter complex: a review

Endoanal ultrasound is now regarded as the gold standard for evaluating anal sphincter pathology in the investigation of anal incontinence. The advent of three-dimensional ultrasound has further improved our understanding of the two-dimensional technique. Endoanal ultrasound requires specialised equipment and its relative invasiveness has prompted clinicians to explore alternative imaging techniques. Transvaginal and transperineal ultrasound have been recently evaluated as alternative imaging modalities. However, the need for technique standardisation, validation and reporting is of paramount importance. We conducted a MEDLINE search (1950 to February 2010) and critically reviewed studies using the three imaging techniques in evaluating anal sphincter integrity.     

Magnetic resonance imaging anatomy of the anal canal

The anatomy of the anal canal is complex but well demonstrated by MRI. Understanding the anatomy is a prerequisite for determining the true site and the extent of pathology, especially for surgical workup. In this article, the MRI anatomy of the anal canal has been displayed using highlighted MRI images and line diagrams.     

Moving-table MR angiography of the peripheral runoff vessels: comparison of body coil and dedicated phased array coil systems

OBJECTIVE: The aim of our study was to compare the signal-to-noise ratio and the diagnostic accuracy of moving-table MR angiography of the peripheral arteries with body coil and dedicated phased array coil systems. SUBJECTS AND METHODS: Forty patients were examined with digital subtraction angiography and moving-table MR angiography with a 1.5-T MR imaging system either with a body coil (n = 20) or with a dedicated phased array coil (n = 20). The timing of contrast material was performed with real-time MR fluoroscopy. RESULTS: For the iliac artery, upper leg, and lower leg, the mean values for signal-to-noise ratios were 56, 51, and 17, respectively, for the body coil, and 54, 74, and 64, respectively, for the dedicated phased array coil. For the body coil, sensitivity and specificity in identifying stenosis greater than 50% and occlusions were 100% and 96%, respectively, for the iliac arteries, and 100% and 96%, respectively, for the upper leg. For the dedicated phased array coil, sensitivity and specificity for stenosis greater than 50% and occlusions were 100% and 96%, respectively, for the iliac arteries, and 100% and 98%, respectively, for the upper leg. Sensitivity and specificity were inferior for the body coil (88% and 85%) compared with the dedicated phased array coil (100% and 96%) in the lower leg. A significant difference of the mean values of contrast-to-noise ratio was found before and after subtraction for the dedicated phased array coil and body-coil techniques (Student's t test, p < 0.01). CONCLUSION: In comparison with the body coil, the dedicated peripheral phased array surface coil system improves signal-to-noise ratio for the upper and lower leg and diagnostic accuracy in the lower leg.     

膝关节的MRI检查

MRI由于具有软组织的良好对比,所以是膝关节内外结构的无创伤性检查方法,对半月板病变诊断,更具有优越性。本文报道25例病人的膝关节MRI检查。50个半月板22个有撕裂。另有3个盘状半月板,1个半月板囊肿,2个后纵韧带损伤。手术9例,8例符合MRI,1例假阳性。T1及质子密度像显示半月板撕裂好,T2加权像显示半月板囊肿和韧带损伤好。     

Magnetic resonance imaging of the primary site in stage I cervical carcinoma: A comparison of endovaginal coil with external phased array coil techniques at 0.5T

OBJECTIVE: To compare endovaginal with pelvic phased array coil magnetic resonance imaging (MRI) in detection of Stage I cervical carcinoma by correlating the findings with histopathology. Patients and METHODS: Forty consecutive patients with Stage I cervical carcinoma confirmed histologically were studied using an endovaginal coil alone immediately followed by a pelvic phased array coil. T1-W transverse and T2-W FSE sagittal images made with each coil were analyzed independently by two radiologists noting the presence and size of a mass within the cervix and any parametrial extension or involvement of adjacent organs. Tumor volumes were measured using the electronic calliper to compute tumor area on each slice and multiplying by the slice thickness. Thirty patients underwent radical hysterectomy, one a trachylectomy, one simple hysterectomy and four extended cone biopsies. Four patients had radiotherapy to the primary tumor. Following surgery, histopathologic findings were recorded and tumor volumes measured. RESULTS: Tumor volumes ranged from 0-106 cm(3)(median 1.4 cm(3), mean 9 +/- 19.4 cm(3)). Thirty-six patients had correlation of the primary site with the surgical specimen. Agreement between observers was excellent for both endovaginal (k = 0.90) and pelvic phased array (k = 0.96) techniques. Combined sensitivity and specificity for both observers of endovaginal MR imaging for detection of tumor was 96% and 70%, respectively; for pelvic phased array imaging sensitivity was substantially less at 54%. Specificity was higher at 83.7%, probably because small abnormalities were seldom visible. In patients treated surgically, early parametrial involvement in four women on endovaginal MRI was confirmed histologically in two. Pelvic phased array imaging showed early parametrial involvement in four women and was confirmed in one. CONCLUSION: Endovaginal MRI adds substantially to information from pelvic phased array images in the preoperative assessment of patients with early cervical cancer. J. Magn. Reson. Imaging 2000;12:1020-1026.     

Determinations of prostate volume at 3-Tesla using an external phased array coil: comparison to pathologic specimens

RATIONALE AND OBJECTIVES: To compare techniques for measuring in vivo prostate volumes using torso phased-array imaging at 3-Tesla. METHODS: Eleven patients imaged at 3-Tesla with a torso-phased array coil using multiplanar fast spin echo (FSE) T2-weighted imaging who underwent radical prostatectomy comprised the study population. Surgical specimens were imaged. The pathologic specimen volume was compared with varieties of magnetic resonance volume determinations, the latter using ellipsoid and planimetric assessments. Three-dimensional images of the excised prostate were generated. Linear correlation coefficients were calculated comparing volume determinations from image data and pathologic data. RESULTS: Correlation coefficient (r2) values from the ellipsoid formula among six different data sets ranging between 0.325 to 0.751; the highest in vivo r2 value was obtained by multiplying the anterior-posterior and the superior-inferior dimensions from the sagittal image by the right-left dimension from the axial image. The r2 values of the planimetric volume and specimen 3-dimensional volume rendering were 0.652 and 0.86, respectively. CONCLUSIONS: Surface coil prostate imaging at 3-Tesla provides undistorted images for volume assessment and in vivo volume determinations very close to ex vivo imaging volume determinations.     

Examination of measurement and its method of compensation of the sensitivity distribution using phased array coil for body scan

The influence on the quality of images by measurement of a sensitivity distribution and the use of a sensitivity compensation filter was considered using an opposite-type phased array coil and volume-type phased array coil. With the opposite-type phased array coil, the relation between coil interval and filter was investigated for the IIC filter, SCIC filter (GE), and the Normalize filter (SIEMENS). The SCIC filter and Normalize filter showed distance dependability over the coil interval of SNR and uniformity was observed, and the existence of an optimal coil interval was suggested. Moreover, with the IIC filter, distance dependability over a coil interval was small, and the decrease in contrast with use was remarkable. On the other hand, with the volume-type phased array coil, the overlap of an array element was investigated to determine the influence it had on sensitivity distribution. Although the value stabilized in the arrangement center of an array element, and its near, was shown when volume-type phased array coil was used, SNR and uniformity decreased as it separated from the center. This showed that overlap of an array element does not have an adverse influence on image quality when the already optimized arrangement is used.     

Comparative evaluation between external phased array coil at 3 T and endorectal coil at 1.5 T: preliminary results

OBJECTIVE: The aim of this study was to compare the image quality and the diagnostic accuracy of endorectal coil 1.5 T MRI (erMRI) and phased-array coil 3 T MRI (3-T MRI) in the pretherapeutic staging of prostate cancer. METHODS: Twenty-nine consecutive patients, with pathological proven prostate cancer, have been examined in the same week with both erMRI and 3-T MRI. Two radiologists independently evaluated the image quality focusing on the following points: cancer tissue conspicuity, capsular infiltration and tumor involvement of seminal vesicles, neuro-vascular bundles, and apex. The radiologists assigned to each one of the above findings an image-quality score ranging from 1 to 5 (with 1 meaning "not visible," 2 "poorly visible," 3 "fairly visible," 4 "well visible with some artifacts," and 5 "clearly visible without artifacts".) Afterwards a comparative evaluation of the mean score obtained respectively by erMRI and 3 T MRI was done. Twenty-two of these 29 patients underwent radical prostatectomy. Assuming as gold standard the pathological report from the resected specimen, we compared the diagnostic accuracy of 3TMRI and erMRI in differentiating between tumors confined within the prostate gland (stage相似文献   

Active device tracking and high-resolution intravascular MRI using a novel catheter-based, opposed-solenoid phased array coil.

A novel two-element, catheter-based phased array coil was designed and built for both active MR device tracking and high-resolution vessel wall imaging. The device consists of two independent solenoid coils that are wound in opposite directions, connected to separate receive channels, and mounted collinearly on an angiographic catheter. The elements were used independently or together for tracking or imaging applications, respectively. The array's dual functionality was tested on a clinical 1.5 T MRI scanner in vitro, in vivo, and in situ. During real-time catheter tracking, each element gave rise to a high-amplitude peak in the respective projection data, which enabled reliable and robust device tracking as well as automated slice positioning. In vivo microimaging with 240 microm in-plane resolution was achieved in 9 s using the device and TrueFISP imaging. Therefore, a single device was successfully implemented that met the combined requirements of intravascular device tracking and imaging.     

The value of respiratory triggered T2-weighted turbo spin-echo imaging of the liver using a phased array coil

The purpose of this study was to evaluate the value of the respiratory triggered turbo spin-echo (TSE) technique for T2-weighted MRI of liver lesions. Fifty-nine patients (32 men, 27 women; mean age, 63.3 years) with focal hepatic lesions were prospectively studied with MRI at 1.5 T with use of a body phased array coil. In the first 15 patients, breath-hold TSE, respiratory triggered TSE, and conventional nonrespiratory triggered TSE T2-weighted imaging were compared. Because nonrespiratory triggered TSE imaging was significantly inferior (P < .01) to breath-hold or respiratory triggered images, breath-hold and respiratory triggered TSE T2-weighted images were compared in the remaining 44 patients. Images were analyzed quantitatively by measuring the liver signal-to-noise ratio and the lesion-liver and spleen-liver contrast-to-noise ratios and qualitatively by evaluating the lesion conspicuity, liver parenchymal homogeneity, and sharpness of intrahepatic vessels. The imaging time was 26 seconds for breath-hold TSE imaging, 49 to 219 seconds (mean, 149 seconds) for the respiratory triggered TSE imaging, and 79 to 379 seconds (mean, 239 seconds) for the nonrespiratory triggered TSE imaging. Quantitatively, the signal-to-noise ratio of the liver for breath-hold imaging was comparable to that for respiratory triggered imaging. The lesion-liver and liver-spleen contrast-to-noise ratios for the respiratory triggered images were greater by 37% and 39%, respectively, than for the breath-hold T2-weighted TSE images. Qualitatively, the respiratory triggered images showed lower frequency of image artifact, better lesion conspicuity, and greatly superior depiction of intrahepatic structures compared with the breath-hold T2-weighted TSE images. The respiratory triggered T2-weighted TSE technique provides better quality liver images than the breath-hold TSE technique or nonrespiratory triggered technique within a reasonable acquisition time.     

Improved homogeneity of the transmit field by simultaneous transmission with phased array and volume coil

Purpose:

To improve the homogeneity of transmit volume coils at high magnetic fields (≥4 T). Due to radiofrequency (RF) field/tissue interactions at high fields, 4 T to 8 T, the transmit profile from head‐sized volume coils shows a distinctive pattern with relatively strong RF magnetic field B₁ in the center of the brain.

Materials and Methods:

In contrast to conventional volume coils at high field strengths, surface coil phased arrays can provide increased RF field strength peripherally. In theory, simultaneous transmission from these two devices could produce a more homogeneous transmission field. To minimize interactions between the phased array and the volume coil, counter rotating current (CRC) surface coils consisting of two parallel rings carrying opposite currents were used for the phased array.

Results:

Numerical simulations and experimental data demonstrate that substantial improvements in transmit field homogeneity can be obtained.

Conclusion:

We have demonstrated the feasibility of using simultaneous transmission with human head‐sized volume coils and CRC phased arrays to improve homogeneity of the transmit RF B₁ field for high‐field MRI systems. J. Magn. Reson. Imaging 2010;32:476–481. © 2010 Wiley‐Liss, Inc.