Effect of prone versus supine patient positioning on pelvic magnetic resonance image quality.

RATIONALE AND OBJECTIVES: Magnetic resonance imaging (MRI) of the pelvis in the prone position has been proposed as a means of reducing motion-related image blurring. The authors performed a randomized controlled trial to determine if patient positioning affects image quality. METHODS: All women undergoing pelvic MRI during a 7-month period, who could lie both prone and supine, were randomized to the supine or prone position. The quality of axial T2-weighted spin-echo images was rated by two radiologists using a 1-to-4 scale (1 = marked blurring to 4 = sharp definition of pelvic structures). RESULTS: Of 78 eligible women, 61 were randomized. Two patients could not complete the examination. The mean image quality rating of 2.8 for the 32 patients imaged prone was not significantly different from the mean rating of 2.9 for the 27 patients imaged supine (P = .5, Mann-Whitney U test). CONCLUSION: Patient positioning did not significantly affect pelvic MRI quality. The choice of patient position should be based on other considerations, such as patient comfort or ease of patient positioning.

Mechanisms of signal loss in magnetic resonance imaging of stenoses.

Some of the factors affecting the signal losses that occur in magnetic resonance images at a stenosis or other region of complex flow have been evaluated. The important determinants of dephasing within a volume element are the net gradient moments, which can be kept small even at long echo times. For compact gradient wave forms, the echo time by itself is unimportant and does not affect signal losses. Reducing the fraction of echo sampled is an alternate method to velocity compensation for reducing gradient moment dephasing that keeps higher moments small. The effects of reducing the fraction of echo sampled on the signal losses in flow distal to a stenosis have been measured experimentally. Another source of signal loss at a stenosis is the variation of the mean phase within a volume element that occurs for flow that varies from one phase encoded view to another. Changes in flow behavior between acquisitions lead to signal displacement in the image. These view to view changes have also been quantified.

Changes in magnetic resonance transverse relaxation times of two muscles following standardized exercise.

Magnetic resonance (MR) imaging studies of exercising leg muscles were performed to compare the changes in MR transverse relaxation times (T2) that result from exercise of the anterior tibialis (AT) and extensor digitorum/hallicus longus (E) in the anterior compartment of the lower leg with those T2 changes in the medial and lateral gastrocnemius (G) in the posterior compartment. Spin-echo MR images were obtained at 1.5 Tesla before and during the first 14 min of recovery from dynamic exercise. In order to normalize the exercise, workloads for each subject were set at 25% of the measured maximum voluntary contraction (MVC) of the anterior and posterior compartments. In separate exercise sessions, a nonmagnetic, pneumatic exercise apparatus was employed for either dorsiflexion or plantarflexion against a fixed constant resistance for two different exercise durations (1 min 45 s or 5 min). Transaxial MR images (TR = 1000 ms, TE = 30, 60, 90, 120 ms, 128 x 256 matrix, 1.5 cm slice) were used to calculate T2 values. Although subjects performed approximately 7-fold more work (P < or = 0.001, dorsiflexion vs plantarflexion) during plantarflexion than during dorsiflexion at both exercise duration's, the exercise induced T2, while being greater than those at rest (P < or = 0.001), were not significantly different in the different compartments. We conclude that, when exercised at the same workload (25% of MVC), these two muscles produce T2 changes that are not significantly different from each other.

Clinical magnetic resonance imaging of articular cartilage.

Magnetic resonance (MR) imaging of articular cartilage has recently become of intense interest because of new developments in the treatment of articular cartilage injury. Recent advances in MR imaging technology has allowed the development of imaging sequences tailored to the assessment of articular cartilage. Several clinical studies have validated the accuracy and reliability of high-resolution, fat-suppressed, three-dimensional, spoiled gradient-recalled MR imaging in the assessment of articular cartilage defects of the knee. The use of other MR imaging techniques is evolving, including the use of fast spin-echo imaging and anionic contrast-enhanced T1-weighted imaging. This article describes the background and rationale to MR imaging of articular cartilage and focuses on its clinical application. Because the knee has been the focus of most research in articular cartilage imaging, the discussion in this article will be largely restricted to this joint.

Pelvic phased array coil: image quality assessment for spin-echo MR imaging.

The NMR phased array coil (PA) provides improved signal-to-noise ratio (SNR) over that available with the body coil. We evaluated image quality obtained with a pelvic PA compared to that obtained with the body coil for spin-echo imaging. Thirty-three women undergoing clinical pelvic MRI were imaged with the body coil followed by imaging with the PA with the same field-of-view (FOV) in 11 patients, and with a small FOV in 23 patients. Image quality was assessed independently by two radiologists. In individual cases there was significant improvement in image quality with the PA, however the expected marked improvement in image quality was not consistently found. Two factors which may limit image quality are increased motion artifact and nonuniformity of signal with distance from the coils. Significant improvements in image quality may occur with improved techniques to decrease motion artifact.

Bone marrow edema in the greater tuberosity of the humerus at MR imaging: association with rotator cuff tears and traumatic injury.

UNLABELLED: The purpose of this study was to determine the prevalence of bone marrow edema in the greater tuberosity of the humerus on MR imaging, the association with other findings at MR imaging and the injury mechanism which can lead to this finding. SUBJECTS AND METHODS: MR reports from 863 patients referred for shoulder MRI over 74 months were reviewed to identify patients with marrow edema in the greater tuberosity. The MR images from patients with greater tuberosity marrow edema were reviewed by consensus of two radiologists for the extent of marrow edema and for associated injuries. Marrow edema in the greater tuberosity was seen in 11 of 863 patients (1.3%). Nine patients (82%) had associated rotator cuff tear by MR imaging (four full thickness and five partial thickness), one patient had avulsion of the greater tuberosity from the humerus, and one had no rotator cuff abnormality. History of trauma was reported by eight patients including fall without direct blow to the shoulder (6), car accident (1) and direct blow to the top of the shoulder (1). Marrow edema in the greater tuberosity is an infrequent finding. Marrow edema most often is associated with a history of trauma and with rotator cuff abnormalities including full thickness tears. The history of trauma without direct blow to the shoulder and the location of the edema indicates that marrow edema often results from avulsion injury by the supraspinatus tendon.

Volumetric flow estimation in vivo and in vitro using pulsed-Doppler ultrasound.

The measurement of volumetric blood flow in small vessels in vitro and in vivo poses a significant technological challenge. In this study, two pulsatile flow models were developed, one with a 3.2-mm lumen diameter and one with a 12.7-mm lumen diameter, to assess the accuracy of volumetric flow estimation of two pulsed-Doppler devices, a Crystal Biotech VF1 20-MHz system with either a cuff-mounted or a needle-mounted probe and an Advanced Technology Laboratories Ultramark 9 High Definition Imaging system with a 5-MHz linear array transducer. The VF1 volumetric flow error was measured in the 3.2-mm phantom over a variety of pulsatile and continuous waveforms. The accuracy of the VF1 was also tested in porcine femoral and renal arteries. VF1 volumetric flow error ranged from 4.8% to 54.3% in the in vivo studies. The ATL demonstrated similar volumetric flow errors in the porcine femoral artery (approximately 3.2 mm diameter), but these errors were reduced to < or = 17.4% in the 12.7-mm-diameter in vitro flow model.

Magnetic resonance imaging of articular cartilage of the knee.

Recently developed magnetic resonance (MR) imaging techniques allow accurate detection of moderate- and high-grade articular cartilage defects. There has been increased interest in MR imaging of articular cartilage in part because it is useful in identifying patients who may benefit from new articular cartilage replacement therapies, including chondrocyte transplantation, improved techniques for osteochondral transplantation, chondroprotective agents, and cartilage growth stimulation factors. The modality also has the potential to play an important role in the follow-up of patients during and after treatment. Detection of articular cartilage defects is beneficial for patients undergoing arthroscopy for other injuries, such as meniscal tears, because the presence of articular cartilage injury worsens prognosis and may modify therapy options.

Magnetic resonance imaging in the evaluation of the portal venous system.

Magnetic resonance (MR) imaging is used in assessing the portal venous system through qualitative and quantitative methods. Magnetic resonance angiography can be performed using time-of-flight or phase-contrast techniques. Time-of-flight techniques (which use gradient echo images to display bright blood or spin echo images to display black blood) are relatively standardized and commercially available. These techniques are used to display liver morphology, portal vein patency, portal venous collaterals, and surgically created portosystemic shunts. Magnetic resonance is equivalent to angiography in the detection of varices, according to a preliminary study. Time-of-flight flow imaging using gradient echo techniques (in which a thrombus appears as absence of bright signal in the portal vein) and spin-echo techniques (where thrombus appears as a bright signal) can become combined to increase specificity for diagnosis of portal vein thrombosis. Phase-contrast techniques provide flow information based on phase shifts induced by flow through magnetic gradients. Phase-contrast angiography is less widely available than time-of-flight angiography. However, phase-contrast methods allow imaging of very slow flow that is not possible using time-of-flight methods. Quantitation of flow is possible, both with time-of-flight techniques using bolus tracking and with phase-contrast techniques using quantitative measurement of phase shifts. Calculations of flow velocity correlate well with Doppler ultrasound estimations, MR flow quantitation does not, at present, rival ultrasound in terms of cost or availability. However, MR is not limited by obesity or overlying bowel gas which can prevent adequate ultrasound evaluation.(ABSTRACT TRUNCATED AT 250 WORDS)

SLAP lesions of the glenoid labrum diagnosed with MR imaging.

Tears of the superior portion of the glenoid labrum in patients without shoulder instability have recently been described. These tears, which include the "anchor" of the biceps tendon to the labrum, have been labeled "SLAP lesions" (superior labrum anterior to posterior). This study was performed to determine the magnetic resonance (MR) findings in patients with SLAP lesions. Retrospective review of the shoulder arthroscopy reports on patients who underwent MR imaging using a 1.5-T unit and subsequent arthroscopy by a single surgeon identified six patients with SLAP lesions (average age 36 years, range 17-65 years). MR images demonstrated atypical morphology indicative of tear in the superior portion of the labrum in four of the six patients, but only one tear had been identified preoperatively. Radiologists interpreting MR images of the shoulder should be aware of the MR findings of SLAP lesions as these tears can be a significant cause of patient disability and are difficult to diagnose clinically.

Clinical imaging of articular cartilage in the knee.

Assessment of articular cartilage has become an essential part of magnetic resonance (MR) evaluation of the knee. This has occurred because of recent advances in treatment along with improved accuracy of MR image evaluation of articular cartilage. Detection of articular cartilage defects can provide an explanation for symptoms and allow identification of patients for cartilage therapy and is an important factor for predicting prognosis of patients with knee injury. This review describes the most easily implemented MR techniques for evaluation of articular cartilage and the normal and abnormal appearance of cartilage seen using these techniques. The influence of imaging findings on treatment is described.

Central osteophytes in the knee: prevalence and association with cartilage defects on MR imaging.

OBJECTIVE: The objective of this study was to determine the prevalence and location of central osteophytes in patients referred for MR imaging of the knee and the relationship of central osteophytes to articular cartilage defects, marginal osteophytes, meniscal tears, and anterior cruciate ligament tears as seen on MR imaging. MATERIALS AND METHODS: Two hundred consecutive patients referred for MR imaging of the knee were evaluated for central osteophytes, articular cartilage defects, marginal osteophytes, meniscal tears, and anterior cruciate ligament tears. A 1.5-T scanner was used, and assessments were made by consensus of two experienced musculoskeletal radiologists. Seven patients were excluded, leaving 193 patients in the study population. RESULTS: The prevalence of central osteophytes in the knee was 15% (35 central osteophytes in 29 patients). Patients with central osteophytes were older (mean age, 52 years versus 38 years), weighed more (mean weight, 204 lb [92 kg] versus 174 lb [78 kg]), had more articular cartilage defects (mean, 4.3 versus 1.3), and had more marginal osteophytes (mean, 3.9 versus 1.1) than patients without central osteophytes (p < 0.0001, Student's t test). Patients with central osteophytes were more likely to have a meniscal tear (p = 0.004, chi-square test), but they were not more likely to have an anterior cruciate ligament tear. All central osteophytes were associated with articular cartilage defects at the same location, which were full or near-full thickness on MR imaging for 32 of 35 central osteophytes. CONCLUSION: Central osteophytes are common in patients referred for MR imaging of the knee. When central osteophytes are seen in the knee there is a high likelihood of an associated full thickness or near-full thickness articular cartilage defect.

Normal and abnormal glenoid labrum: assessment with multiplanar gradient-echo MR imaging.

A retrospective study of magnetic resonance (MR) imaging of the glenoid labrum performed with multiplanar gradient-echo (MPGR) sequences was done to ascertain the different appearances of the normal labrum and the findings in patients with tears. MPGR images were obtained with a 1.5-T magnet in 37 shoulders of 16 healthy subjects and 19 patients with subsequent surgical evaluation. Increased intralabral signal intensity was seen in 12 of 26 normal shoulders (46%), and atypical morphology was seen in six shoulders (23%). Atypical morphology was present in eight of nine patients with labral tears. Deformity (n = 2 [22%]) and clefts (n = 2 [22%]) were seen in patients with tears. Deformity (n = 3 [12%]) and clefts (n = 1 [4%]) were occasionally seen in healthy subjects. Absence of the labrum and separation of the labrum from the glenoid cavity was present only in patients with tears; therefore, the labrum should be presumed torn in the presence of these findings. Increased intralabral signal intensity on MPGR images did not help predict labral integrity; morphologic findings were more predictive of labral tear.

Submucosal uterine leiomyomas: diagnosis of prolapse into the cervix and vagina based on MR imaging.

OBJECTIVE: We describe the MR appearance, signs and symptoms, and pathologic findings in five patients with submucosal leiomyomas that prolapsed into the cervical or vaginal canal. SUBJECTS AND METHODS: During the past 3 years, five women aged 33-53 years (mean, 43 years) were identified prospectively at MR imaging as having prolapsing uterine leiomyomas. The diagnosis was confirmed by surgical pathology. MR imaging was performed on a 1.5-T unit, using both T1- and T2-weighted spin-echo or fast spin-echo sequences. The images were analyzed for signal intensity, presence of a stalk, and caudal extent of the prolapsed leiomyoma. RESULTS: These leiomyomas, the presence of prolapse, and the caudal extent of prolapse were detected prospectively on MR images in all five cases. Prospective localization of the stalk in two cases aided subsequent hysteroscopic resection. MR imaging correctly indicated the presence of hemorrhage in one, degeneration in a second, and the absence of these complications in two others. In the fifth case, a hemorrhagic focus in the distal tip of the leiomyoma was not detected on MR images obtained 3 days before surgery. CONCLUSION: MR imaging is useful for the diagnosis and characterization of uterine leiomyomas that have prolapsed into the cervical or vaginal canal.

MR imaging of articular cartilage.

With the advent of new treatments for articular cartilage disorders, accurate noninvasive assessment of articular cartilage, particularly with MR imaging, has become important. Understanding the MR imaging features of articular cartilage has led to the development of two types of routinely available MR imaging techniques which have demonstrated clinical accuracy and interobserver reliability.

Articular cartilage defects: in vitro evaluation of accuracy and interobserver reliability for detection and grading with US.

PURPOSE: To determine the accuracy and reliability of detecting and grading articular cartilage defects in porcine and human knees by using ultrasonography (US). MATERIALS AND METHODS: US was used to evaluate 175 porcine and 16 human knee surfaces with a linear 5-12-MHz transducer. Porcine defects of varying diameter and depth were surgically created. Each porcine surface was independently assessed in blinded fashion by two radiologists for the presence and severity of defects. Accuracy of detection, interobserver reliability, and concordance between US and surgical grades were determined. Human specimens were retrieved from knees of patients who underwent joint arthroplasty. Defects in human knees detected with US were correlated with defects seen at direct surface visualization. RESULTS: Sensitivities for detection of porcine defects were 94% and 93% for readers 1 and 2, respectively; specificities were 90% and 77%, respectively; positive predictive values were 98% and 95%, respectively; and negative predictive values were 78% and 73%, respectively. Interobserver agreement was high (weighted kappa = 0.80), and concordance between US and surgical grades for both readers was high (weighted kappa = 0.90 and 0.78). In human cartilage, the distribution of cartilage denudation determined at US was the same as that determined at direct visualization. CONCLUSION: High-frequency US was accurate and reliable for detection and grading of knee articular cartilage defects.

Detection of knee hyaline cartilage defects using fat-suppressed three-dimensional spoiled gradient-echo MR imaging: comparison with standard MR imaging and correlation with arthroscopy.

OBJECTIVE: A preliminary study was done to prospectively compare fat-suppressed three-dimensional spoiled gradient-echo (3D SPGR) MR imaging with standard MR imaging for detection of defects in the hyaline cartilage of the knee, using arthroscopy as the reference standard. SUBJECTS AND METHODS: We studied 43 consecutive patients referred by two orthopedic surgeons for MR imaging of the knee. Twelve had arthroscopic correlation; they formed the basis of our study. Hyaline cartilage was imaged with a fat-suppressed 3D SPGR sequence with previously determined optimal imaging parameters. Our standard MR imaging study consisted of two-dimensional coronal T1-weighted spin-echo, sagittal dual-echo T2-weighted spin-echo, and axial multiplanar gradient-echo sequences. With arthroscopy as the reference standard, sensitivity and specificity of fat-suppressed 3D SPGR and standard MR images for detecting cartilage tears were determined by articular surface (eight surfaces in each patient: medial and lateral patellar facets, trochlear facets, femoral condyles, and tibial plateaus). Statistically significant differences in sensitivity and specificity were determined. RESULTS: Arthroscopy showed 15 cartilage defects in seven patients. The fat-suppressed 3D SPGR images had higher sensitivity (93%) than the standard MR images (53%, p = .03). Specificity was 94% for the fat-suppressed 3D SPGR images compared with 93% for the standard MR images (p > .05). The five false-positive articular surfaces on fat-suppressed 3D SPGR images were from focal signal change within the substance of the cartilage without a contour defect. Smoothly contoured thinning and loss of the trilaminar appearance of the hyaline cartilage at the lateral femoral notch was shown in all subjects and was considered a normal finding. CONCLUSION: Fat-suppressed 3D SPGR imaging is more sensitive than standard MR imaging for the detection of abnormalities of the hyaline cartilage in the knee. Routine use of this technique may strengthen the role of MR imaging for noninvasive evaluation of internal derangements of the knee.

Internal derangements of the knee: rates of occurrence at MR imaging in patients referred by orthopedic surgeons compared with rates in patients referred by physicians who are not orthopedic surgeons.

PURPOSE: To compare the occurrence at magnetic resonance (MR) imaging of clinically important knee abnormalities in patients referred by orthopedic surgeons with that in patients referred by other physicians. MATERIALS AND METHODS: Knee MR images in all patients referred for evaluation of internal derangement for 12 months were retrospectively reviewed. Meniscus, ligament, and articular cartilage abnormalities were tabulated. The numbers of abnormalities detected in the patients referred by orthopedic surgeons were compared with those in the patients referred by all other physicians by using chi(2) analysis. Significance was defined at P less than .05. RESULTS: Knee MR images in 439 patients were reviewed; 328 patients were referred by orthopedic surgeons, and 111 were referred by other physicians. There was no significant difference in the rates of occurrence of meniscus tear (149 [45%; orthopedic surgeon referrals] vs 50 [45%; other physician referrals], P = .96); ligament tear (82 [25%] vs 21 [19%], P = .25); isolated hyaline cartilage defect (77 [23%] vs 20 [18%], P = .29); meniscus or ligament tear (167 [51%] vs 55 [50%], P = .86); or meniscus, ligament, or articular cartilage tear (242 [74%] vs 72 [65%], P = .34). The proportion of patients who subsequently underwent surgery of the knee was also similar (39% [118 of 300] vs 28% [23 of 82], P = .14). CONCLUSION: There was no significant difference in the occurrences of clinically important knee internal derangement at MR imaging between patients referred by orthopedic surgeons and those referred by other physicians.

Effect of hydration status on renal medulla attenuation on unenhanced CT scans.

OBJECTIVE: The purpose of this study was to assess the effect of hydration status on renal medulla attenuation during unenhanced CT. SUBJECTS AND METHODS: An unenhanced CT scan was obtained in 10 healthy men after 12-18 hr of complete fluid restriction and again after rehydration. CT images were reviewed for the presence and extent of dense renal medulla, defined as greater attenuation than the adjacent cortex. CT findings were correlated with urine-specific gravity and osmolality. RESULTS: Eight of the 10 subjects showed dense renal medulla on a CT scan after dehydration. After rehydration, complete resolution was seen on the CT scan in four of the eight subjects; three of the eight subjects showed a decrease in the extent of dense renal medulla. After rehydration, the eighth subject showed a slight increase in the attenuation of the renal medulla on the CT scan. Dense renal medulla was seen significantly more often on dehydration images (p = .035). CONCLUSION: Increased renal medulla attenuation on an unenhanced CT scan can be a normal finding related to dehydration.

Chondromalacia patellae: diagnosis with MR imaging.

Most previous studies of MR imaging for detection of chondromalacia have used T1-weighted images. We correlated findings on axial MR images of the knee with arthroscopic findings to determine MR findings of chondromalacia patellae on T2-weighted and proton density-weighted images. The study population included 52 patients who had MR examination of the knee with a 1.5-T unit and subsequent arthroscopy, which documented chondromalacia patellae in 29 patients and normal cartilage in 23. The patellar cartilage was assessed retrospectively for MR signal and contour characteristics. MR diagnosis based on the criteria of focal signal or focal contour abnormality on either the T2-weighted or proton density-weighted images yielded the highest correlation with the arthroscopic diagnosis of chondromalacia. When these criteria were used, patients with chondromalacia were detected with 86% sensitivity, 74% specificity, and 81% accuracy. MR diagnosis based on T2-weighted images alone was more sensitive and accurate than was diagnosis based on proton density-weighted images alone. In conclusion, most patients with chondromalacia patellae have focal signal or focal contour defects in the patellar cartilage on T2-weighted MR images. These findings are absent in most patients with arthroscopically normal cartilage.