Hyaline articular cartilage: relaxation times,pulse-sequence parameters and MR appearance at 1.5 T

In order to optimize the parameters for the best visualization of the internal architecture of the hyaline articular cartilage a study both ex vivo and in vivo was performed. Accurate T1 and T2 relaxation times of articular cartilage were obtained with a particular mixed sequence and then used for the creation of isocontrast intensity graphs. These graphs subsequently allowed in all pulse sequences (spin echo, SE and gradient time (TR), echo time (TE) and flip angle (FA) for optimization of signal differences between MR cartilage zones. For SE sequences maximum contrast between cartilage zones can be obtained by using a long TR (> 1,500 ms) with a short TE (< 30 ms), whereas for GRE sequences maximum contrast is obtained with th shortest TE (< 15 ms) combined with a relatively long TR (> 400 ms) and an FA greater than 40°. A trilaminar appearance was demonstrated with a superficial and deep hypointense ozne in all sequences and an intermediate zone that was moderately hyperintense on SET1-weighted images, slightly more hyperintense on proton density Rho and SE T2-weighted images and even more hyperintense on GRE images.     

Interactions of paramagnetic contrast agents and the spin echo pulse sequence

The theoretical equations for paramagnetic contrast agent effects and the spin echo pulse sequence are combined to graph magnetic resonance (MR) intensity as a function of paramagnetic contrast agent concentration for various tissues. Analysis of the graphs and equations demonstrate several technical and clinical implications. These include: (1) positive enhancement is most likely to occur with short TEs and TRs; (2) changes in machine parameters TE and TR will change the concentration of agent at which the peak enhancing MR intensity will occur; (3) there is an absolute maximum MR intensity that can be reached with contrast enhancement; (4) the maximum MR intensity reached with enhancement is dependent on the tissues' T2 and, to a lesser degree, T1 relaxation times; (5) certain TE and TR combinations will cause no enhancement; (6) if positive enhancement does occur, it will usually occur only over a limited range of agent concentration; and (7) the tissues' T1 relaxation time but not its T2 time determines whether positive enhancement will occur and the relative amount of enhancement.     

Urinary bladder MR imaging. Part I. Normal and benign conditions

The normal urinary bladder and several benign entities of the bladder were examined in 50 patients by magnetic resonance (MR) imaging. Specific features assessed included appearance of the bladder wall, optimal repetition (TR) and echo delay (TE) parameters for bladder-wall demonstration, and differentiation among various benign abnormalities, including bladder-wall hypertrophy, inflammation, and mucosal congestion, on MR images. The bladder wall in the 30 healthy subjects was best displayed using a TR = 2 sec, TE = 56 msec image, which gave 60% contrast between the bladder wall and urine and 48% contrast between the bladder wall and fat. Demonstration of bladder-wall hypertrophy required similar imaging; bladder distention was necessary to demonstrate the thickness of the bladder wall. Congestion and inflammation were best demonstrated on TR = 2 sec, TE = 56 msec images, which gave 45% contrast. Normal and/or hypertrophic bladder wall were distinguished from inflammation and congestion on the basis of signal intensity variations and/or T1 and T2 relaxation parameters.     

Optimization of the techniques for studying the upper abdomen with magnetic resonance. II. Changes in the intrinsic contrast

Magnetic Resonance imaging of the upper abdomen was performed on more than 300 patients. The aim of the study was to determine the influence of spin-echo parameters on intrinsic image contrast. Different TR (ranging 260 to 2000 ms) and TE (ranging 20 to 120 ms) values were employed in two patients with a hepatic metastases and in a healthy volunteer with a hepatic cyst. The highest liver-to-lesion contrast was observed when the shortest TR and TE values (260 and 20 ms, respectively) were used, while the lesions appeared isointense with the surrounding parenchyma with TR 800 ms. In T2-weighted images TR 2000 ms allowed the complete recovery of longitudinal magnetization, giving a contrast relative only to the T2 of the lesion.     

Quantitative analysis of sodium fast and slow component in in vivo human brain tissue using MR Na image]

In vivo sodium concentrations in the normal brain tissue and a tumorous tissue were analyzed using MR Na image. The nuclear magnetic resonance enabled us to divide the signal from sodium in the living tissue into 2 parts based on the differences of T2 value. Those are fast component having the T2 value of less than 5 msec and slow component of 15-40 msec. We investigated the effect of macromolecules on T2 value of sodium image using polyvinyl alcohol (PVA) powder. MR Na image was taken with the parameters of TR/TD, 110 ms/1.9 ms (FID image) and TR/TE, 110 ms/20 ms (SE image). Saline solution showed high intensity on both FID image and SE image. Saline solution added PVA (PVA phantom) also showed high intensity on FID image, whereas the signal intensity of PVA phantom in SE image extinguished. To know the relation between the signal intensity and sodium concentration, sodium concentration--signal intensity curve was obtained using phantoms with various sodium concentrations (0.05-1.0%). This curve showed a direct proportion between sodium concentration and signal intensity on Na image. We measured further the sodium concentrations of the human brain tissue. Sodium phantoms were arranged around the heads and the MR Na images of the normal brains from 3 volunteers and a patient with a brain tumor (meningioma) were taken. The sodium concentrations of occipital lobe, basal ganglia and the tumorous tissue were calculated using the sodium concentration--signal intensity curve obtained from the phantoms arranged around the heads.(ABSTRACT TRUNCATED AT 250 WORDS)     

Optimization of the technic in the study of the upper abdomen using magnetic resonance. I. Artifact reduction

Complete motion artifact suppression is possible in abdominal MR imaging with the simple optimization of sequence parameters, with no need for special softwares. The authors have studied the influence of sequence parameters modification on the signal/noise relation and on the presence of motion artifacts. The tested parameters included Repetition Time (TR), 150 to 2000 ms, Echo Time (TE), 20 to 120 ms, and the number of acquisitions, 2 to 16. In T1-weighted sequences, the major advantages were offered by the short TR and short TE association, with many acquisitions. Optimal signal/noise relation and complete motion artifact suppression were thus obtained. In T2-weighted sequences, TE values had to be changed according to the desired contrast enhancement, and the number of acquisitions could not be increased to more than 2 in order to keep the acquisition time short.     

MR imaging evaluation of plica synoviallis mediopatellaris of the knee joint]

To evaluate the diagnostic ability of MR imaging for plica synoviallis mediopatellaris (PSM), we retrospectively reviewed the MR imaging findings of patellofemoral space in 20 knee joints of 11 patients. In all 20 knee joints, arthroscopy and MR imaging were available. MR imaging was performed with a 1.5 Tesla Magnetom (Siemens) using a round surface coil. Pulse sequences were SE (TR 600 ms/TE 26 ms), SE (TR 200 ms/TE 26, 70 ms) and FLASH (TR 450 ms/TE 15 ms/FA 90 degrees). In six of the 20 knees with PSM proved by arthroscopy, a low intensity band was shown above the medial condyle of the femur on both T1- and T2-weighted MR images, and on FLASH images this band was shown as intermediate intensity. In the other 14 knees with no PSM observed by arthroscopy, the low intensity band was not shown on MR imaging. In all 20 knees, a similar low intensity band was shown about 1 cm cranial to the medial condyle of the femur. This should not be diagnosed as PSM. The low intensity band seen on T1- and T2-weighted MR images and its anatomical relation to the medial condyle are important in diagnosing PSM.     

Optimization of a dual echo in the steady state (DESS) free-precession sequence for imaging cartilage

Three-dimensional (3D) MR imaging of the knee is useful to detect cartilage abnormalities, although the tissue contrast in 3D gradient-recalled echo (GRE) sequences such as gradient-recalled acquisition in the steady state (GRASS) or fast low-angle shot (FLASH) is poor. T2 contrast can be added to a GRASS sequence by combining the signals from the first and second gradient echoes, which form immediately after and immediately before each radiofrequency (RF) pulse in a 3D GRE sequence. We have optimized a 3D dual echo in the steady state (DESS) sequence, which produces one averaged image from the two echoes, for use in the detection of articular cartilage abnormalities. In the optimization process, we examined the imaging parameters of flip angle (α), repetition time (TR), echo time (TE), and bandwidth to maximize the contrast between cartilage and joint fluid. A theoretical simulation of the sequence was confirmed with experiments conducted on phantoms with known T1 and T2. On the basis of theoretical predictions and experiments using healthy volunteers, we determined that an optimized sequence with a bandwidth of 98 Hz per pixel, a TR of 30 msec, a TE of 7.1 msec, and an α of 60° produced the highest contrast between cartilage and fluid within a defined acquisition time of 6 minutes. Additional contrast was obtained by filtering the second-echo image to eliminate noise before adding it to the first-echo image.     

Relative intensity of abdominal organs in MR images

Knowledge of the normal relative intensity of organs and tissues is a valuable aid to clinical interpretation of magnetic resonance images. In this study the in vivo spin echo image intensities of normal parenchymal organs and other structures in the upper abdomen were evaluated for eight parameter combinations. The examinations of 40 patients were used. Image intensity and calculated T1, T2, and spin density values were obtained for liver, spleen, pancreas, renal cortex, renal medulla, bone marrow, skeletal muscle, and fat. Repetition times (TR) of 500, 1,000, 1,500, and 2,000 ms and echo times of 28 and 56 ms were used. The T1 and T2 values and relative spin density were calculated using a new algorithm. Liver had the smallest relative standard deviation of T1 of all the tissues studied. For comparison purposes, relative image intensities were calculated by normalizing them to the intensity of liver in the same image. The resulting compiled data show the normal ranks and ranges for relative intensity for the tissues in each of eight types of spin echo images. Although images with short TR and echo time (TE) are known to display the greatest T1 contrast, the mean relative intensities of all tissues except muscle and fat in the TR = 500 and TE = 28 ms images were within 20% of liver. A much larger spread in the normal relative intensities was observed with longer TE and TR.     

Hand-held electronic teaching-aid for demonstrating MRI concepts

We describe a hand-held electronic teaching-aid for magnetic resonance imaging (MRI), which can be used to demonstrate the dependence of signal intensity on changing pulse sequence parameters (TR and TE), the dependence of intensity on changing tissue parameters (T1 and T2), and the ideas of "T1-weighting" and "T2-weighting" as they relate to image contrast. The device was specifically designed to be easy to use and readily accessible to residents-in-training and MR neophytes.     

Uterine leiomyomas: correlation of MR, histopathologic findings, and symptoms

Magnetic resonance (MR) imaging, symptoms, and pathologic findings were correlated in 59 uterine leiomyomas from 23 patients. The tumors varied from less than 1 cm to 18 cm in diameter. Fifty-seven leiomyomas were identified in the corpus uterus, one was located within the broad ligament, and another was detected in the cervix. Among the corpus lesions, 9 were correctly identified on MR images as subserosal and 37 as intramural. Of 11 tumors assigned at surgery to the submucosal group, 10 had been accurately defined with MR. On MR, myomas associated with hypermenorrhea produced an anatomic disruption of the "junctional zone" (the low-intensity band seen at the myometrium-endometrium junction on T2 contrast images). Long TR (2 sec) and TE (56 msec) parameters (T2 contrast images) yielded the best contrast resolution between leiomyoma and surrounding myometrium. Correlation of MR with histologic features demonstrated 2 groups of lesions. Leiomyomas free of degenerative changes emitted homogeneous signals of low intensity. Contrast between tumor and myometrium was -16% on the T1 contrast image and increased to -44 +/- 16% on the T2 contrast image. Leiomyomas with hyaline, myxomatous, or fatty degeneration demonstrated various degrees of inhomogeneity, best seen on images obtained with long TR and TE. It is concluded that MR is an accurate modality for imaging uterine leiomyomas, since it clearly demonstrates tumor number, size, location, and the presence and extent of degeneration.     

ESWAN序列参数对出血性剪切灶及脑静脉显示的影响和分析

目的研究多回波采集的增强T2*加权血管成像(ESWAN)序列的TR和TE参数对磁敏感效应的影响;调整更适合出血性剪切灶检出的ESWAN序列参数。资料与方法 10例弥漫性轴索损伤(DAI)患者经两种不同参数设置的ESWAN序列(两种序列的参数区别在于:短TE的ESWAN序列的首个回波TE 10 ms,TR 77 ms;长TE的ESWAN序列的首个回波TE 48 ms,TR 104 ms)扫描获得两组ESWAN图像,经后处理得到两组幅度图,将幅度图行最小强度投影(MinIP)后在两组图像上分别计数出血灶的数目、测量出血灶的容积,在三脑室上部及室间孔层面对显影的脑深部静脉计数。用配对t检验的方法检验两组数据的差异性。结果两组图像显示的微出血灶的数量及分布完全一致;长TE的ESWAN序列测量的微出血灶容积显著大于短TE的ESWAN序列;长TE的ESWAN序列显示的脑深部静脉数量明显多于短TE的ESWAN序列。结论 ESWAN序列的多回波采集优势,即使明显缩短首个回波的TE,后续的回波仍能保障对微出血灶检出的磁敏感效应;随着TE的延长,显影的静脉数量明显增多,但模糊效应也逐步放大,出血灶容积的放大比例也增加。对于脑外伤...     

Musculoskeletal MR imaging: turbo (fast) spin-echo versus conventional spin-echo and gradient-echo imaging at 0.5 tesla

The value of T2-weighted fast spin-echo imaging of the musculoskeletal system was assessed in 22 patients with various neoplastic, inflammatory, and traumatic disorders. Images were acquired with high echo number (i.e., echo train length) fast spin-echo (FSE; TR 2000 ms, effective TE 100 ms, echo number 13, lineark-space ordering), conventional spin-echo (SE; TR 2000 ms, TE 100 ms) and gradient-echo (GRE) sequences (TR 600 ms, TE 34 ms, flip angle 25°). Signal intensities, signal-to-noise ratios, contrast, contrast-to-noise ratios, lesion conspicuousness, detail perceptibility, and sensitivity towards image artifacts were compared. The high signal intensity of fat on FSE images resulted in a slightly inferior lesion-to-fat contrast on FSE images. However, on the basis of lesion conspicuity, FSE is able to replace time-consuming conventional T2-weighted SE imaging in musculoskeletal MRI. In contrast, GRE images frequently showed superior lesion conspicuity. One minor disadvantage of FSE in our study was the frequent deterioration of image quality by blurring, black band, and rippling artifacts. Some of these artifacts, however, can be prevented using short echo trains and/or short echo spacings.     

Lymph nodes of the neck. Diagnosis using magnetic resonance with gradient-echo technique

As for the pathologic conditions of neck lymph nodes, the clinician needs to know if the involved node is reactive, phlogistic, or neoplastic in nature. If accurate tumor staging is required, imaging techniques play a fundamental role. Our study was aimed at assessing the actual role of MR imaging in the evaluation of neck lymph node involvement. The study was performed using an MR Max Plus by General Electrics operating with an 0.5 T superconductive magnet. We employed gradient-echo (GE) pulse sequences with TR 500, TE 15 ms and 90 degrees flip angle for T1-weighted images, and with TR 500, TE 30 ms and 25-30 degrees flip angles for T2-weighted images; for Pd-T2-weighted images, TR was 520, TE 30 ms, and flip angles were 40-45 degrees. The results were correlated with histopathologic findings obtained at biopsy. The advantages of GE sequences were: 1) whole neck imaging--thus saving time, and reducing radiation dose and contrast media; 2) optimal anatomical and topographic evaluation of the lesion; 3) imaging of the longitudinal diameter of the node; 4) higher sensitivity for lymph node tissue modifications; 5) imaging of necrosis, hemorrhage, and/or fibrosis. GE sequences were especially useful for accurate tumor staging, in the follow-up, and to verify response to therapy. However, even though MR imaging has proven to have high sensitivity, its specificity was similar to that of contrast-enhanced CT. Further studies with the use of paramagnetic contrast media are needed to solve these problems.     

Undescended testis: value of MR imaging

Magnetic resonance (MR) imaging was performed in 32 male patients, 20 with no abnormalities and 12 with clinically suspected undescended testes. The results were compared with ultrasonographic, computed tomographic, clinical, and surgical findings. The undescended testes were unilateral in eight patients (one had testicular duplication) and bilateral in four. Of 16 undescended testes, 15 were correctly identified on MR images. One intraabdominal testis was not seen. Testis-fat contrast at 0.35 T was optimal with a short repetition time (TR) and a short echo time (TE). At 1.5 T, good contrast was achieved with short TR/TE sequences, but the contrast was even more pronounced with even longer TR/TE parameters. In seven patients with unilateral undescended testes, the undescended and contralateral testes showed symmetrical tissue signal intensity on both T1- and T2-weighted images. In three, the undescended testis was of lower signal intensity, suggesting atrophy. MR imaging promises to become an important diagnostic tool in the detection of undescended testes.     

Preliminary clinical results with low flip angle spin-echo MR imaging of the head and neck

A new approach for producing primarily T2- and proton-density-weighted MR images in less time than the conventional long TR, long TE imaging is to reduce the TR of a double spin-echo pulse sequence and to also reduce the RF excitation flip angle to minimize the resulting T1 sensitivity. In preliminary studies with a human volunteer and five patients with various diseases of the head and neck, conventional long TR, long TE and short TR, short TE images were compared with short TR, long TE images with reduced flip angles (45 degrees, 30 degrees), which required only 40% of the imaging time of the long TR images. The latter images showed a similar contrast pattern to the conventional T2-weighted image, and contrast-to-noise measurements indicated an increase in contrast between the lesion and nearby tissue when the flip angle was reduced. Furthermore, the maximum contrast/noise per unit imaging time on the short TR, long TE image was comparable to that on the long TR, long TE image. Optimization of the flip angle with short TR allows a substantial reduction in imaging time but with a reduction in multislice capability. This technique will be most useful in areas of complex anatomy where two or more orthogonal imaging planes are required, such as the head and neck.     

MR imaging of intramuscular hemorrhage

This retrospective study was performed to (a) analyze the appearance of normal striated muscle using the spin echo (SE) technique and (b) evaluate the potential of magnetic resonance (MR) imaging for demonstrating intramuscular bleeding. Magnetic resonance examinations of 30 patients imaged for reasons other than muscular disorders were reviewed. Normal striated muscle was always imaged with a lower intensity than fat because muscle had a longer T1 and a shorter T2 than fat. Furthermore, the spin density of muscle was less than that of fat. The best contrast between the two tissues was obtained with a short repetition time (TR) of 0.5 s and a long echo time (TE) of 56 ms. In addition, five MR examinations from three patients with intramuscular bleeding were assessed. In one case the CT examination was also available for comparison. In every case MR permitted the diagnosis and demonstrated the precise extent of intramuscular bleeding and its regression after therapy. The MR diagnosis of intramuscular bleeding was readily performed because of the excellent contrast resolution of the technique. These lesions were always brighter than the surrounding normal muscle. The optimum SE technique, which enhanced contrast between the muscle and the site of bleeding, was a long TR of 2.0 s and a long TE of 56 ms. The T1 and T2 relaxation times of intramuscular bleeding were always longer than those of normal striated muscle. Preliminary results indicate that MR is very sensitive for the demonstration of intramuscular bleeding.     

Fast recovery 3D fast spin-echo MR imaging of the inner ear at 3 T

High-resolution MR imaging of the inner ear with a heavily T2-weighted 3D fast spin-echo sequence has been performed successfully at 1.5 T. However, at 3 T, the longer T1 time of CSF necessitates a longer TR, resulting in significantly prolonged imaging times. In this study, the fast recovery 3D fast spin-echo sequence, which permits the TR to be reduced while maintaining T2 contrast, was optimized at 3 T for imaging of the inner ear. The optimized sequence parameters are as follows: 1500/294 (TR/TE); echo spacing, 18.1 ms; bandwidth, 38 kHz at 512 readout; and imaging time, 13 minutes.     

Instant images of the body by magnetic resonance

Proton magnetic resonance (MR) body images of the normal, adult human which have total scan times of typically only 40 ms per image are presented. There is no loss of spatial or contrast resolution due to motional blurring or ghosting; rather, movie loops of multiple 40-ms images directly demonstrate normal respiratory and peristaltic motion. Manifestation of "traditional" relaxation time contrast is demonstrated for a variety of spin echo (TE) and image repetition (TR) times. The images, obtained at 2.0 T on a new high-speed MR system, have a signal-to-noise ratio for muscle of approximately 30:1 (TE = 30 ms) for a 4.7-mm slice thickness (voxel size = 0.08 cm3). In a study presented as an example, 140 images covering the body from diaphragm to pelvis were all obtained within approximately 10 min. This method may help improve the efficacy of MR body imaging in general, and may play a role in applications which require high temporal resolution.     

Contrast-enhanced MRI of periarticular soft-tissue changes in experimental arthritis of the rat

This study was to determine if manipulation of magnetic resonance signal intensity by means of an intravenously injected paramagnetic contrast agent is useful for the detection and characterization of periarticular inflammation. Arthritis was induced in 20 rats by means of intradermal injection of Freund's complete adjuvant. MR imaging was performed with a resistive magnet operating at 0.35 T. A double spin-echo technique with TE's of 28 and 56 ms and TR's of 0.5 and 2.0 s was used. The hindpaws of the adjuvant-injected rats were imaged on Day 8, Day 11, or Day 15 following injection of the adjuvant. The images were obtained in the transverse plane before and after intravenous injection of gadolinium-DTPA (0.2 mmol/kg). Because of their long T2 relaxation time, inflammatory lesions were characterized by high MR signal intensity on precontrast images obtained with long TR and long TE (T2-weighted images). On the other hand, because of their long T1 relaxation time, the inflammatory lesions were of relatively low intensity and not easily recognized on precontrast images obtained with short TR and short TE (T1-weighted images). Postcontrast T1-weighted images were also sensitive in detecting periarticular inflammation as a result of T1 shortening by the gadolinium-DTPA. However, in our particular model, the data did not indicate any greater MR sensitivity for detecting arthritis by means of gadolinium-DTPA enhancement.