Juvenile rheumatoid arthritis: assessment with MR imaging

Thirty-three joints of the appendicular skeleton in 15 children with juvenile rheumatoid arthritis were examined with magnetic resonance (MR) imaging to determine if it could demonstrate synovial hypertrophy and status of the articular cartilage. Presumed synovial hypertrophy was seen in 13 joints as masses of varying sizes of low to intermediate signal intensity on T1- and T2-weighted images; sometimes foci of increased signal intensity, most likely due to fluid or inflammation, were seen on T2-weighted images. Probable abnormal articular cartilage was detected in ten joints, and MR imaging also demonstrated epiphyseal overgrowth, bone erosions, joint effusions, and joint space narrowing. Because MR imaging appears to provide an objective method of evaluating both synovial hypertrophy and status of articular cartilage, it may prove to be useful in monitoring progression of juvenile rheumatoid arthritis and response to therapy.     

Patellar articular cartilage lesions: in vitro MR imaging evaluation after placement in gadopentetate dimeglumine solution

PURPOSE: To evaluate T1-weighted magnetic resonance (MR) imaging after diffusion of gadopentetate dimeglumine for visualization of articular cartilage lesions. MATERIALS AND METHODS: MR imaging was performed in eight human cadaveric patella specimens immediately and 4 hours after placement into a vessel filled with gadopentetate dimeglumine solution (2.5 mmol/L). T1-weighted spin-echo and inversion-recovery turbo spin-echo MR sequences with nulled cartilage signal (inversion time of 300 msec) were used. In a total of 128 articular cartilage areas, MR imaging findings were compared with macroscopic and histopathologic findings. Pathologic evaluation was performed by one musculoskeletal pathologist. With knowledge of pathologic observations, MR images were analyzed by one musculoskeletal radiologist with regard to intrinsic signal intensity characteristics and surface abnormalities of articular cartilage. RESULTS: Histopathologic findings demonstrated 67 areas of normal articular cartilage and 66 cartilage lesions (grade 1, n = 19; grade 2, n = 15; grade 3, n = 26; grade 4, n = 6). All grade 3 and 4 lesions could be identified on MR images obtained immediately after submersion and after 4 hours. Ninety-four percent of grade 1 and 2 lesions were identified as areas of predominantly decreased contrast enhancement on delayed MR images obtained with both sequences. MR images obtained immediately after submersion demonstrated abnormal signal intensity in only 9% and 12% of grade 1 and 2 lesions, respectively. CONCLUSION: T1-weighted MR images obtained in vitro after gadopentetate dimeglumine diffusion allow demonstration of articular cartilage surface lesions and early stages of cartilage degradation.     

Amyloid arthropathy of the hip joint: MR demonstration of presumed amyloid lesions in 152 patients with long-term hemodialysis

The aim of this study was to determine the spectrum of MR findings of presumed amyloid arthropathy of the hip joints in patients on long-term hemodialysis. We prospectively performed T1- and T2-weighted spin-echo imaging on 152 consecutive patients on hemodialysis. The duration of hemodialysis ranged from 5 months to 24 years, 2 months (mean: 8 years, 8 months). The frequency, location, and signal intensity of bone lesions were assessed. In 12 cases with contrast-enhanced MR examination, enhancement pattern of bone lesions, synovial lesions, and intra-articular lesions were characterized. Bone lesions presumed to be amyloid deposits were identified in 60 patients (39 %). Magnetic resonance imaging revealed that amyloid lesions were more extensive than anticipated by plain radiographs. All bone lesions showed decreased signal intensity on T1-weighted images. On T2-weighted images, bone lesions showed increased signal intensity in 32 patients (54 %), decreased signal intensity in 11 patients (18 %), and both increased and decreased signal intensity in 17 patients (28 %). Following intravenous injection of gadolinium-based contrast, all bone lesions showed moderate enhancement. Synovial thickening could not be identified on T1- and T2-weighted images. However, contrast-enhanced images showed thickened synovial membrane, which could be differentiated from joint fluid. Intra-articular nodules showed decreased or intermediate signal intensity on T1-weighted images and decreased signal intensity on T2-weighted images; the intra-articular nodules were contiguous with subchondral bone lesions. Magnetic resonance imaging is useful for evaluating the distribution and extent of amyloidosis of the hip joints in patients undergoing long-term hemodialysis. Received 5 August 1997; Revision received 22 October 1997; Accepted 11 February 1998     

血友病性关节病的MRI分析

目的:探讨血友病性关节病的MRI表现及临床价值.方法:回顾性分析11例22个膝关节血友病性关节病患者的MRI表现.结果:22个膝关节均有积血,表现为关节腔、骨骼和/或软组织血肿,早期血肿在T1WI为等信号、T2WI呈高信号;中期血肿在T1WI呈略高信号或混杂信号,T2WI呈高信号或混杂信号;晚期血肿在T1WI和T2WI均表现为混杂信号,血肿逐渐被吸收.病变早期关节结构基本保持正常,中晚期关节结构均有损害,表现为关节软骨、骨皮质破坏吸收,关节间隙狭窄,骨端或骨骺增大变形.早中期滑膜、关节囊、肌肉及韧带肿胀,而晚期则萎缩、退变.结论:MRI能准确显示血友病性关节病的病理改变,对疾病分期、指导临床治疗及同位素放射治疗效果评价具有重要意义.     

Articular cartilage defects: detectability in cadaver knees with MR

The capability of 1.5-T MR imaging to detect focal defects in articular cartilage was investigated with cadaveric knees with and without intraarticular injection of saline and gadolinium-DTPA (Gd-DTPA). Full-thickness cartilage lesions ranging in diameter from 1 to 5 mm were surgically created in the femoral articular surfaces. Images were acquired with a variety of pulse techniques, slice thicknesses, and interslice gaps as well as one or two signal excitations. Potential intraarticular contrast agents (saline and Gd-DTPA) were tested, and their signal behaviors compared with that of hyaline cartilage. All cartilage defects were occult on T1-weighted and balanced images without Gd-DTPA. The smallest defect identified by using intraarticular saline was 3 mm in diameter and was apparent only on T2-weighted images. Intraarticular Gd-DTPA afforded detection of defects as small as 2 mm, even with short imaging times. Signal-intensity differences between saline and articular cartilage were minimal on T1-weighted images and increased on T2-weighted images; intensity differences were high between Gd-DTPA and articular cartilage on all imaging sequences. These results indicate that intraarticular fluid and appropriate selection of imaging sequences are necessary for delineation of focal defects in articular cartilage. They also show that Gd-DTPA is the optimal contrast agent for this purpose.     

Sacroiliitis: MR imaging findings

Magnetic resonance (MR) imaging was performed in seven asymptomatic volunteers and 17 patients with clinical and radiologic evidence of sacroiliitis. MR imaging findings were compared with those at computed tomography (CT) to determine the MR imaging appearance of the sacroiliac joint when normal and in sacroiliitis. The normal articulation was well depicted with MR imaging. Findings of sacroiliitis were identified in 20 sacroiliac joints (12 patients). MR imaging findings characteristic of sacroiliitis included abnormal cartilage signal intensity (95% of joints) and erosions (75% of joints) on T1-weighted images. Areas of increased intensity in the articulation (80% of joints) or in erosions (60% of joints) were seen on T2-weighted images. MR imaging was superior to CT for evaluation of cartilage and detection of erosions. Four sacroiliac joints (20%) and two patients (17%) with MR imaging findings of sacroiliitis were negative at CT. The authors conclude that MR imaging is a valuable method for detecting sacroiliitis, particularly when results of other imaging techniques are inconclusive.     

High-resolution magnetic resonance imaging of normal porcine cartilaginous epiphyseal maturation

The aim of this study was to determine whether highresolution magnetic resonance (MR) imaging could differentiate epiphyseal and articular cartilage in the cartilaginous epiphysis and demonstrate its developmental changes. T1- and T2-weighted (T1W and T2W) spin-echo sequences at 50-mm field of view (FOV) of hip joints were obtained from 14 piglets (newborn to 6 months). Subsequently, high-resolution MR images (15-mm FOV) of a biopsy core of the proximal femoral cartilaginous epiphysis were correlated with histology. Newborn cartilaginous epiphysis demonstrated homogeneous signal intensity on T1W and T2W imaging with abundant cartilage canals. From 2 weeks of age, the cartilaginous epiphysis showed a diminution of cartilage canals, with three zones evident on T2W imaging consisting of a low-signal middle zone separating two higher signal zones. Histologic evaluation demonstrated four distinct morphologic laminas with a decrease in overall cartilage thickness with age. The laminas were not as well defined in the newborn compared with the older piglets. No simple correlation was found between the MR zonal pattern and the morphological laminas on histology. No distinct demarcation between the articular cartilage and epiphyseal cartilage was present. MR can visualize cartilage canals and demonstrate changes in the cartilaginous epiphysis that occur with maturation. What component of the cartilaginous epiphysis that accounts for the MR differences seen between newborn and older piglets remains unclear.     

Signs of patellar chondromalacia on sagittal T2-weighted magnetic resonance imaging

We incidentally noted distinctive high signal defects or fissures in the patellar articular cartilage on sagittal T2-weighted magnetic resonance (MR) images in 4 patients. At subsequent arthroscopy all 4 patients were found to have patellar chondromalacia. To determine the reliability of these signs, we retrospectively evaluated, in a blinded manner, sagittal T2-weighted MR images of the knee in 75 patients who were undergoing arthroscopic assessment of their patellar articular cartilage. We identified high signal defects or fissures in the patellar cartilage of 5 patients. Patellar chondromalacia was noted at arthroscopy in all 5 patients. Arthroscopy demonstrated patellar chondromalacia in an additional 21 patients with normal MR images. We conclude that high signal defects or fissures on sagittal T2-weighted images are useful signs of patellar chondromalacia. This single imaging sequence will, however, detect only a small number of the cartilage lesions that may be present.     

MR imaging of the postoperative knee: a pictorial essay.

Magnetic resonance (MR) imaging of the postoperative knee has become more common because more arthroscopic repair procedures are being performed. The most common procedures include partial meniscectomy and meniscal repair, anterior cruciate ligament (ACL) reconstruction, and cartilage repair procedures. Specific findings of a retorn meniscus following meniscal repair or partial meniscectomy are increased signal intensity extending through the site of repair on T2-weighted images, displaced meniscal fragments, and abnormal signal intensity at a site distant from the repair. Findings of ACL graft disruption on T2-weighted MR images include absence of intact graft fibers and increased signal intensity similar to that of fluid within the expected region of the graft. Partial tears of the graft appear as areas of increased signal intensity affecting a portion of the graft with some intact fibers still present. An impinged ACL graft may appear to be draped over the anterior inferior edge of the intercondylar roof or be posteriorly bowed. Localized anterior arthrofibrosis appears on T1-weighted MR images as a focal nodular lesion of low signal intensity that is anterior to the ACL graft in the intercondylar notch and is indistinguishable from adjacent joint fluid. On T2-weighted images, the nodule is well differentiated from high-signal-intensity joint fluid. Finally, MR imaging has been shown to be accurate in the evaluation of cartilage repair tissue. Knowledge of the normal MR imaging appearance of the knee after the more common repair procedures will allow radiologists to recognize complications associated with such procedures.     

Magnetic resonance imaging in hemophilic arthropathy of the knee

The MR findings at the examination of 16 knees in 9 hemophilic patients were reviewed. The hemophilic arthropathy was demonstrated in great detail. The state of the joint cartilage, menisci, posterior cruciate ligaments and synovial tissue could be assessed. The presence of intraarticular hemorrhage and cyst fluid in bone cavities was recorded. MRI may become a valuable tool for assessment of early treatment of hemophilic arthropathy.     

Meniscal tears: MR and arthrographic findings after arthroscopic repair

Magnetic resonance (MR) imaging was performed on 29 previously repaired menisci and one conservatively treated meniscus (total, 30 menisci). Intermediate- and T1-weighted MR sequences revealed persistent signal intensity extending to an articular surface (grade 3 signal intensity) in 27 of the 30 menisci. On T2-weighted images, seven of the 30 menisci were found to contain unequivocally higher signal intensity, defined by a full-thickness defect (grade 3 signal intensity involving two articular surfaces) increasing in signal intensity to a level equivalent to that of joint fluid. The MR imaging and arthrographic appearances of 23 of the 30 menisci were compared. Arthrographic examination revealed partial or complete healing in 13 menisci and tears in 10. The presence of grade 3 signal intensity on intermediate- and T1-weighted MR images did not reliably predict a tear seen at arthrography. Unequivocally higher signal intensity on T2-weighted images is a useful sign in the prediction of a persistent meniscal tear (sensitivity, 60%; specificity, 92%; P less than .02). Since presence of grade 3 signal intensity on intermediate- and T1-weighted images does not reliably predict a tear and unequivocal T2 increase in intensity has a sensitivity of only 60%, arthrography should be considered for assessment of the symptomatic, previously repaired meniscus.     

强直性脊柱炎骶髂关节影像学分析(附24例骶髂关节平片、CT和MR影像对比观察)

目的：旨在评估强直性脊柱炎（ＡＳ）患者骶髂关节炎的ＭＲ影像特征，并比较Ｘ线平片、ＣＴ和ＭＲ影像在诊断骶髂关节炎中的作用。材料与方法：搜集２４例ＡＳ患者，分别行Ｘ线平片、ＣＴ和ＭＲＩ检查。增强前ＭＲ扫描序列包括ＳＥＴ１ＷＩ、ＦＳＥＴ２ＷＩ和梯度回波的准Ｔ２ＷＩ（ＧＲＴ２＊ＷＩ）。增强后ＭＲ扫描序列参数与增强前ＳＥＴ１ＷＩ相同。另选９例志愿者，行ＭＲ平扫检查。结果：８例志愿者１６个骶髂关节的Ｔ１ＷＩ和Ｔ２ＷＩ可直接显示正常骶髂关节软骨，表现为线形或点样的中等信号影。９例志愿者１１个骶髂关节的骨髓内可见局灶性脂肪沉积。２４例ＡＳ患者的４２个骶髂关节可见软骨异常，表现为Ｔ１ＷＩ和Ｔ２ＷＩ上正常线形中等信号的软骨影像消失，代之以不规则增粗或扭曲样中等信号。分析表明：在骶髂关节炎的诊断方面，ＭＲ和ＣＴ明显优于Ｘ线平片（Ｐ＜０．００１）。结论：同Ｘ线片比较，虽ＣＴ和ＭＲＩ均有助于ＡＳ骶髂关节炎的诊断，但ＭＲ影像可显示ＣＴ和Ｘ线所不能显示的软骨异常和骨髓内水肿改变；骨髓内脂肪沉积可属正常变异；扭曲样中等强度信号应视为软骨的异常征象。     

Structure, function, and degeneration of bovine hyaline cartilage: assessment with MR imaging in vitro

The basic magnetic resonance (MR) imaging pattern of normal and degenerated hyaline articular cartilage was studied in vitro in 40 fresh bovine patellae. With the use of an ample spectrum of strongly T1- to T2-weighted sequences, two zones of cartilage with different signal intensities were observed in all specimens. A superficial cartilaginous layer in the MR image with higher water content and longer T1 and T2 correlated with the tangential and transitional zones of normal articular cartilage, whereas a second MR imaging zone with shorter T1 and T2 was identified in the depth of the articular cartilage. Different functional properties in pressure resistance were observed in the two layers. In early cartilage degeneration without thinning, there was increased hydration of the superficial cartilage layer. This study suggests that strongly T1- and T2-weighted images are indispensable for evaluating details in articular cartilage degeneration.     

Evaluation of chondromalacia of the patellofemoral compartment with axial magnetic resonance imaging

Axial magnetic resonance (MR) imaging of the patellofemoral compartment was performed in 75 patients with arthroscopic correlation. Proton density and T2 (2500/20/80) weighted images were obtained in all patients. Chondromalacia in stages I and II could not be reliably identified with MR imaging. For the evaluation of stage III and IV chondromalacia, the accuracy of MR was 89%. Focal or diffuse areas of increased or decreased signal alterations of the hyaline cartilage without a contour deformity or cartilaginous thinning do not correlate reliably with arthroscopic staging of chondromalacia. A normal signal intensity is no assurance that softening of the cartilage is not present. The most reliable indicators of chondromalacia are focal contour irregularities of the hyaline cartilage and/or thinning of the hyaline cartilage associated with high signal intensity changes within frank defects or contour irregularities with T2-weighted images. The poor MR-arthroscopic correlation in earlier stages of chondromalacia may be due in part to the subjective basis of the arthroscopic diagnosis. In conclusion, stage I and II chondromalacia of the patellofemoral compartment cannot be reliably evaluated with MR imaging. Stage III and IV chondromalacia is reliably evaluated with MR using the combination of proton density and T2-weighted images.Presented to the Radiological Society of North America, Chicago, November 15–30, 1990     

MR appearance of cartilage defects of the knee: preliminary results of a spiral CT arthrography-guided analysis

The aim of this study was to determine signal intensity patterns of cartilage defects at MR imaging. The MR imaging (3-mm-thick fat-suppressed intermediate-weighted fast spin-echo images) was obtained in 31 knees (21 male and 10 female patients; mean age 45.5 years) blindly selected from a series of 252 consecutive knees investigated by dual-detector spiral CT arthrography. Two radiologists determined in consensus the MR signal intensity of the cartilage areas where cartilage defects had been demonstrated on the corresponding reformatted CT arthrographic images. There were 83 cartilage defects at spiral CT arthrography. In 52 (63%) lesion areas, the MR signal intensity was higher than that of adjacent normal cartilage with signal intensity equivalent to (n=31) or lower than (n=21) that of articular fluid. The MR signal intensity was equivalent to that of adjacent normal cartilage in 17 (20%) lesion areas and lower than that of adjacent cartilage in 8 (10%) lesion areas. In 6 (7%) lesion areas, mixed low and high signal intensity was observed. The MR signal intensity of cartilage defects demonstrated on spiral CT arthrographic images varies from low to high on fat-suppressed intermediate-weighted fast spin-echo MR images obtained with our equipment and MR parameters.     

Articular cartilage of knee: normal patterns at MR imaging that mimic disease in healthy subjects and patients with osteoarthritis

PURPOSE: To evaluate normal magnetic resonance (MR) imaging findings that may mimic articular cartilage diseases in healthy subjects and patients with osteoarthritis of the knee. MATERIALS AND METHODS: Sagittal fat-suppressed intermediate-weighted fast spin-echo (FSE) (repetition time msec/echo time [TE] msec, 4,000/13), sagittal T2-weighted FSE (4,000/39), and sagittal fat-suppressed three-dimensional (3D) spoiled gradient-echo (SPGR) (60/5, 40 degrees flip angle) MR images were acquired in 28 patients and four volunteers. FSE images with a TE of 13 msec were considered "short-TE images"; those with a TE of 39 msec were considered "long-TE images." Presence of normal MR imaging appearance of articular cartilage was determined by one author. Contrast between cartilage and adjacent structures (meniscus, joint capsule, synovial fluid, muscle) was calculated in posterior regions of the femoral condyle on images obtained with each sequence; Wilcoxon signed rank testing was performed. RESULTS: The following appearances were observed in patients with knee osteoarthritis (on short-TE FSE, long-TE FSE, and SPGR MR images, respectively): (a) ambiguity of surface contour in posterior region of the femoral condylar cartilage (in zero, zero, and 20 patients), (b) linear area of high signal intensity in deep zone adjacent to subchondral bone of femoral condyle (in zero, zero, and 26 patients), (c) pseudolaminar appearance in posterior region of femoral condylar cartilage (in seven, nine, and 24 patients), (d) truncation artifact in patellofemoral compartment (in seven, six, and 27 patients), (e) susceptibility artifact on cartilage surface caused by air or metal (in three, three, and 11 patients), (f) decreased signal intensity in distal part of trochlear cartilage (in 28, 28, and 28 patients), (g) cartilage thinning adjacent to the anterior horn of the lateral meniscus (in 19, 19, and 21 patients), and (h) focal cartilage flattening in posterior region of femoral condyle (in 16, 16, and nine patients). Cartilage-meniscus and cartilage-synovial fluid contrast was significantly higher on fat-suppressed FSE than on fat-suppressed 3D SPGR MR images (P <.001). CONCLUSION: Fat-suppressed FSE and 3D SPGR MR images showed nonuniform signal intensity arising from articular cartilage and cartilage thinning, both of which could mimic disease.     

The cartilage black line sign: an unexpected MRI appearance of deep cartilage fissuring in three patients

Many patterns of cartilage signal anomalies have been described in the knee since the advent of magnetic resonance imaging (MRI). With the now widespread use of preoperative MRI, some of these anomalies have proven to represent true pathology, while others have been shown to be normal variants or artifacts at arthroscopy. We describe three patients with an MR cartilage abnormality, not previously illustrated in the literature, consisting of a thin dark signal line on T2-weighted imaging, oriented perpendicular to the plane of imaging. This aberration proved to represent a deep cartilage cleft at arthroscopy (two patients) and at CT arthrography (one patient). Such full thickness fissures are generally considered to have the opposite appearance, that of fluid signal intensity on T2-weighted images.     

Hemophilic arthropathy. A scoring system for magnetic resonance imaging

The aim of this study was to define a system for scoring hemophilic arthropathy (HA) based on MR findings, providing for objective evaluation of the degree of joint involvement and evolution after on-demand administration of FVIII substitutional therapy or prophylactic treatment. A total of 133 MR examinations (89 basal and 44 during follow-up) were performed in 25 patients. Patients were divided in two groups depending on the therapy received and the length of time that the disease had been evolving at the start of the study. Group I was composed of 10 patients with secondary prophylaxis and group II was composed by 15 treated on demand. T1-weighted and T2*-weighted images performed on a 0.5-T unit were prospectively evaluated. The joint involvement was established on a scale of 0 (no abnormalities), I (minimal amount of hemosiderin), II (large amount of hemosiderin and isolated cartilaginous erosion), III (cartilage destruction, bone erosions, and subchondral cysts) to IV (large internal joint derangement, secondary osteoarthritis and/or ankylosis). At basal MR examination, patients of group I showed no abnormalities ( n=28, 75.6%), grade I ( n=3), and grade II ( n=6) of HA. Patients of group II corresponded to MR grades III ( n=21) and IV ( n=11) of HA. The MR follow-up showed improvement in three joints of group I and worsening in 5 joints in group I and 2 joints in group II. Early signs of HA were detected in 10 joints with MR imaging but were underestimated on plain radiographs. Advanced degrees of HA were classified as severe under both imaging techniques. Magnetic resonance is the preferred imaging technique to assess HA. The earliest signs of joint damage, detected by MR, are overlooked by plain radiography. The MR scoring system can be used for evaluating HA. Follow-up MR should be performed to evaluate regression or worsening of the abnormalities, primarily in the case of patients with prophylaxis who usually suffer normal or early joint involvement not detected by other means.     

Evaluation of patellar chondromalacia with MR: comparison between T2-weighted FSE SPIR and GE MTC

PURPOSE: To compare two different MR sequences to tissue signal suppression in the study of patellar cartilage abnormalities. MATERIALS AND METHODS: We examined 26 patients with magnetic resonance (MR) imaging: sequences included spectral presaturation with inversion recovery (SPIR), with fat suppression and T2-weighted images, magnetization transfer contrast (MTC) sequences, T1-weighted and T2-weighted spin-echo sequences. All patients underwent conventional knee arthroscopy and in all patients a hyaline cartilage lesion was assessed in three articular zones: the patellar medial facet, the lateral facet and the patellar crista. Was assessed 78 articular facets. The lesions were classified using a standard arthroscopic grading system adapted to MR imaging: normal cartilage that corresponds to the grade 0 according to the Noyes grading system, low grade lesions that correspond to the grade I e IIa and high grade lesions that correspond to grades IIb and III. The arthroscopic results were compared with MR images. We assessed the MR diagnostic accuracy, sensitivity, specificity and MR positive predictive value and negative predictive value of the two sequences taking into consideration total lesions, and high-grade and low grade lesions separately. RESULTS: Twenty-four low grade lesions (16 grade I e 8 grade IIa) and 18 high grade lesions (10 grade IIb e 8 grade III) were diagnosed by arthroscopy. Regarding low grade and high-grade lesions together, the accuracy was 77% for MTC sequences and 90% for SPIR sequences. In identifying low-grade lesions, the sensitivity was 88% for SPIR sequence and 42% for MTC sequences. Specificity for the detection of all lesions was 89% for the SPIR sequences and 94% for the MTC sequences. The SPIR sequence visualised water content abnormalities in degenerating cartilage, which are representative of low-grade lesions. The sensitivity of the sequence enabled us to obtain improved contrast for detecting cartilage surface irregularities. The MTC sequences allowed us to grade high-grade lesions susceptible to surgery and small cartilage defects in the presence of joint fluid. The MTC sequences were insufficient in the diagnosis of early stages of chondromalacia because the suppression of the signal of bonded water reduced the contrast among areas of articular cartilage with different water content. For this reason cartilage oedema and early superficial fibrillation were not identified. CONCLUSIONS: In our experience the SPIR sequence proved superior to the MTC sequence in the identification of low grade lesions of the patellar cartilage. The overall value of such sequences in the study of articular pathology also needs to be assessed in the others sites where the articular cartilage is thinner and surfaces more curvilinear.     

Incorporation versus infection of retroperitoneal aortic grafts: MR imaging features

The magnetic resonance (MR) imaging characteristics of normal aortic graft healing were compared with those of perigraft infection in 57 patients after aortic graft implantation. Thirty-three patients without postoperative complications underwent MR imaging in a 0.35-T unit 1 week after graft implantation, and 13 of those patients were reexamined 2-3 months after graft implantation. Twenty-four patients with clinically suspected perigraft infection underwent MR imaging 6 weeks to 18 years after graft implantation. Early normal postoperative changes were characterized by a perigraft collar of low to medium signal intensity on T1-weighted images and of high intensity on T2-weighted images in all 33 cases, consistent with perigraft fluid collection. In 10 of 13 patients reexamined 2-3 months postoperatively, the MR images demonstrated a collar of tissue consistent with perigraft fibrosis. In cases of clinical suspicion of retroperitoneal graft infection, MR imaging showed eccentric fluid collections of low to medium signal intensity on T1-weighted images and high intensity on T2-weighted images at more than 3 months after surgery. The MR findings were diagnostic of retroperitoneal perigraft infection in 17 of 20 patients shown to be infected at surgery. Retroperitoneal infection was correctly excluded on the basis of MR findings in four patients. Thus, MR imaging is an accurate imaging method for the diagnosis of aortic graft infection. In the early postoperative phase, resolving perigraft fluid cannot be differentiated from perigraft infection.