Quantitative assessment of an MR technique for reducing metal artifact: application to spin-echo imaging in a phantom.

OBJECTIVE: To quantify image artifact reduction using a new technique (MARS--metal artifact reduction sequence) in vitro. DESIGN: Coronal T1-weighted MR images were obtained through two metal phantoms (titanium/chromium-cobalt and stainless steel femoral prostheses) immersed in water. Comparison of artifact volume was made with images obtained using conventional and modified (MARS) T1-weighted sequences. Signal intensity values outside a range of +/-40% the average signal intensity for water were considered artifact and segmented into low or high signal artifact categories. Considering the arbitrary selection of this threshold value, volumetric calculations of artifact were also evaluated at +/-50%, 60%, 70%, and 80% the mean signal for water. RESULTS: Conventional T1-weighted images produced 87% more low signal artifact and 212% more high signal artifact compared with the MARS modified T1-weighted images of the stainless steel prosthesis. Conventional T1-weighted images of the titanium prosthesis produced 84% more low signal artifact and 211% more high signal artifact than the MARS modified sequence. The level of artifact reduction was essentially uniform for the various threshold levels tested and was greatest at +/-20% the global signal intensity average for water. CONCLUSION: The MARS technique reduces the volume of image signal artifact produced by stainless steel and titanium/chromium-cobalt femoral prostheses on T1-weighted spin-echo images in a tissue phantom model.

MRI of spinal hardware: comparison of conventional T1-weighted sequence with a new metal artifact reduction sequence.

OBJECTIVE: This study was designed to compare diagnostic quality of MR images of patients with spinal hardware acquired using a conventional T1-weighted spin-echo sequence and a new metal artifact reduction sequence (MARS). CONCLUSION: The new MARS sequence effectively reduces the degree of tissue-obscuring artifact produced by spinal fixation hardware and subjectively improves image quality compared with the conventional T1-weighted spin-echo sequence.

Metal artifact reduction sequence: early clinical applications.

Artifact arising from metal hardware remains a significant problem in orthopedic magnetic resonance imaging. The metal artifact reduction sequence (MARS) reduces the size and intensity of susceptibility artifacts from magnetic field distortion. The sequence, which is based on view angle tilting in combination with increased gradient strength, can be conveniently used in conjunction with any spin-echo sequence and requires no additional imaging time. In patients with persistent pain after femoral neck fracture, the MARS technique allows visualization of marrow adjacent to hip screws, thus enabling diagnosis or exclusion of avascular necrosis. Other applications in the hip include assessment of periprosthetic soft tissues after hip joint replacement surgery, postoperative assessment after resection of bone tumors and reconstruction, and localization of unopacified methyl methacrylate cement prior to hip arthroplasty revision surgery. In the knee, the MARS technique allows visualization of structures adjacent to implanted metal staples, pins, or screws. The technique can significantly improve visualization of periprosthetic bone and soft-tissue structures even in patients who have undergone total knee arthroplasty. In patients with spinal fixation hardware, the MARS technique frequently allows visualization of the vertebral bodies and spinal canal contents. The technique can be helpful after wrist fusion or screw fixation of scaphoid fractures.

CT evaluation of periacetabular osteotomies.

We have previously described a simple and reproducible three-dimensional technique of CT for the measurement of the cover of the femoral head in acetabular dysplasia in adults. We now describe the application of this technique in ten patients with symptomatic dysplasia to assess the degree and direction of dysplasia and to measure the cover obtained at acetabular osteotomy. The indices obtained gave a useful indication of the degree and direction of the dysplasia and confirmed which components had been used most efficiently to achieve cover. The information is easily presented in graphical form and gives a clearer indication of the cover obtained than the indices derived from plain radiographs.

Talocalcaneal coalition. Diagnosis with the C-sign on lateral radiographs of the ankle.

We analysed 42 weight-bearing lateral radiographs of the ankle, 20 of which were from patients with a clinical and plain radiological diagnosis of talocalcaneal coalition (TCC) who subsequently had CT. The remainder were from 22 healthy volunteers with no clinical findings suggestive of hindfoot pathology. Four observers, blinded to the CT findings, independently evaluated the radiographs on two separate occasions. With the 95% confidence interval and using the CT findings as the comparison we calculated the sensitivity, specificity, accuracy, and positive and negative predictive values for the C-sign, and for other signs known to be associated with TCC. Similarly, we also calculated the interobserver and intraobserver reliability for these signs using the kappa statistic. Our results suggest that the C-sign is highly sensitive and specific for TCC. It is an accurate indicator and significantly more reliable than other previously recognised radiological signs of TCC. Features of the C-sign, however, cannot be relied upon to indicate whether the TCC is fibrous or bony.

Shoulder after rotator cuff repair: MR imaging findings in asymptomatic individuals--initial experience.

PURPOSE: To assess the magnetic resonance (MR) imaging appearance of the successfully repaired rotator cuff in an asymptomatic population. MATERIALS AND METHODS: Fifteen subjects who had undergone clinically successful rotator cuff repair were included in the study. All underwent functional testing of the affected shoulder and had good to excellent scores on the Constant scale. Standard MR imaging sequences were performed at 1.5 T, including oblique coronal fast spin-echo T2-weighted MR imaging with fat saturation. RESULTS: Three (10%) of 30 supraspinatus and infraspinatus tendons had normal signal intensity, and 16 (53%) had mildly increased signal intensity on fast spin-echo T2-weighted fat-saturated images, compatible with tendonitis or tendinosis. Three partial and four complete tears of the supraspinatus tendon and two partial and two complete tears of the infraspinatus tendon were seen. Other findings included subacromial-subdeltoid effusion (10 subjects), joint effusions (five subjects), and bone marrow edema (six subjects). CONCLUSION: Postoperative signal intensity changes consistent with tendonitis or tendinosis were common, and clinically "silent" partial and complete rotator cuff tears were seen. Such postoperative MR imaging findings should be interpreted with caution, and meticulous correlation with symptoms and clinical results is recommended.

Monoarticular synovial lesions: radiologic pictorial essay with pathologic illustration.

A wide variety of common focal monoarticular synovial lesions may be encountered on imaging studies. A multi-modality approach to these lesions, with appreciation of the differing appearances, can often yield the correct diagnosis. This pictorial essay demonstrates and describes the imaging with illustration of pathologic findings in a spectrum of conditions.

Ulnar nerve injuries of the hand producing intrinsic muscle denervation on magnetic resonance imaging.

Muscle and nerve injuries in the hand may be difficult to detect and diagnose clinically. Two cases are reported in which magnetic resonance imaging showed ulnar nerve injury and intrinsic hand muscle denervation. The clinical, anatomical and radiological features of injury to the deep motor branch of the ulnar nerve and associated muscle denervation are discussed and illustrated.

Carotid artery stenosis in patients who have undergone radiation therapy for head and neck malignancy.

Although it is established that small and medium sized arteries undergo extensive radiation damage, the effect on large vessels such as the carotid arteries is less well understood. We sought to determine if an increased severity of carotid artery stenosis is present in patients who have undergone radiotherapy for head and neck tumours. 45 patients aged 43-90 years (average 67) with head and neck malignancies treated with radiotherapy underwent colour Doppler ultrasonographic scanning of the carotid arteries. These patients were compared with a population of asymptomatic historical controls. 60% of patients demonstrated stenosis ranging from 21 to 86%. 38% of patients demonstrated a stenosis greater than or equal to 50%. Carotid artery stenosis appears to be increased in patients who have previously undergone treatment with radiotherapy to the head and neck regions compared with controls (p < 0.001). These findings suggest that radiation has an adverse effect on large vessels. Colour Doppler follow-up may be indicated for patients receiving head and neck radiation therapy.

Malignant fibrous histiocytoma of soft tissue imaging with emphasis on MRI.

Malignant fibrous histiocytoma (MFH) is the most common soft tissue sarcoma in adults. This pictorial essay describes and illustrates the clinical, pathologic, and radiologic features of MFH. The cross-sectional imaging features on CT and MRI are emphasized in relation to the diagnosis and staging of MFH.

Three-dimensional CT measurement of adult acetabular dysplasia: technique, preliminary results in normal subjects, and potential applications.

OBJECTIVE: To assess a three-dimensional computed tomography (3DCT) technique for measurement of acetabular coverage in adults. DESIGN: We used 3DCT to define the geometric centre of the femoral head and to measure centre-edge angles (CEAs) at 10 degrees rotational increments around the acetabular rim. The means, ranges, standard deviations and 95% confidence intervals for the CEAs at the various rotational increments were determined. Inter- and intra-observer variability was measured. The normal values are compared with two example cases of acetabular dysplasia. PATIENTS: The normal hips of 15 subjects aged 1949 years (mean 34.2 years) were measured. RESULTS: The 3DCT measurements are reproducible (mean difference interobserver, 1.7 degrees - 7.9 degrees; mean difference intra-observer, 0.6 degrees-6.9 degrees). Mean normal CEA at the lateral rim was 33 degrees with a 95% confidence interval of 23 degrees - 43 degrees. Mean normal CEAs at 10 rotational increments from anterior to posterior rim were determined, and graphed as a 'normal curve'. CONCLUSION: This new 3DCT method of assessing acetabular dysplasia is simple, reproducible, and applicable to diagnosis, quantification and surgical planning for adult acetabular dysplasia patients.

Epithelioid angiosarcoma arising in a surgically constructed arteriovenous fistula: a rare complication of chronic immunosuppression in the setting of renal transplantation.

Immunosuppression in the setting of solid organ transplantation is associated with the development of a variety of malignant tumors, most commonly squamous carcinomas and non-Hodgkin's lymphomas. Sarcomas, apart from Kaposi's sarcoma, are relatively infrequent. We recently encountered a 71-year-old man with chronic renal failure, treated by allograft kidney transplantation, who developed a high-grade epithelioid angiosarcoma at the site of a nonfunctioning arteriovenous fistula, previously constructed for hemodialysis. At diagnosis, the patient had numerous satellite nodules of angiosarcoma involving the distal skin, soft tissues, and bones. After a below-elbow amputation, there was a rapid local recurrence at the amputation stump. Currently, the patient is alive with numerous pulmonary metastases, 6 months after amputation. A literature review identified three recently reported identical cases of epithelioid angiosarcoma arising in nonfunctioning arteriovenous fistulae. All three patients had been treated by kidney transplantation for renal failure, suggesting a possible causal association between these events. We performed polymerase chain reaction for human herpes virus 8, the recently recognized herpes virus proposed as a major etiologic agent of Kaposi's sarcoma, and possibly some conventional angiosarcomas, but we failed to identify any viral DNA within the tumor.

Pictorial review: giant cell tumours of bone.

Giant cell tumour of bone is a relatively common neoplasm with limited potential for metastatic spread. These tumours usually occur at the ends of bones with their epicentre in the epiphysis. This essay will review the various common and some of the less frequently encountered manifestations of giant cell tumours at multiple different sites, as well as postoperative recurrence. Different imaging modalities including plain film, tomography, computed tomography and magnetic resonance imaging are shown.

Diagnostic accuracy of helical CT for detection of blunt bowel and mesenteric injuries.

OBJECTIVE: To determine the diagnostic accuracy of helical computed tomography (CT) in the detection of blunt bowel and mesenteric injury in a clinical setting. MATERIALS AND METHODS: We evaluated the helical CT and surgical findings in 31 patients with blunt abdominal trauma. Nineteen patients had surgically proven bowel and/or mesenteric injury, and 12 patients had no bowel or mesenteric injury at laparotomy. The CT scans were assessed by three observers in consensus and were graded as showing no injury, minor bowel or mesenteric injury (not requiring urgent surgery), or major bowel or mesenteric injury (requiring immediate surgery). The CT diagnoses were compared with the surgical findings. RESULTS: In the 19 cases of surgically proven bowel injury, CT had an accuracy of 84% (26/31), specificity 84% (16/19), and negative predictive value 89% (16/18) for diagnosis of bowel injury. CT correctly differentiated minor from major bowel injuries in eight of 12 cases (75%). For the 13 cases of mesenteric injury, the accuracy of CT diagnosis was 77% (24/31), specificity 67% (12/18), and negative predictive value 93% (12/13) for diagnosis of mesenteric injury. The CT findings allowed correct differentiation of minor from major mesenteric injuries in seven of 13 cases (54%). CONCLUSION: Helical CT is moderately accurate and has a high negative predictive value in detecting bowel and mesenteric injuries after blunt trauma. Helical CT is not highly accurate in predicting the severity of injury or need for urgent surgery.

Gadolinium-enhanced dynamic MRI of the fractured carpal scaphoid: preliminary results.

The aim of the present report was to evaluate the vascularity of fracture fragments of the fractured carpal scaphoid in the acute (< 4 weeks) and chronic (> 3 months) phases using a gadolinium-enhanced dynamic MRI sequence. Eight patients with acute scaphoid fractures, six patients with chronic scaphoid fractures, and three control patients without fractures were evaluated using a T1-weighted fast spoiled gradient recalled acquisition (fSPGR) sequence with gadolinium-DTPA enhancement (0.1 mmol/kg bodyweight). Signal intensity over time plots were obtained using region of interest measurements from both fracture fragments. Enhancement factors (EF) were then calculated from the plots. No enhancement of the scaphoid was seen in control subjects (EF: distal scaphoid pole 1.04 +/- 0.01, proximal pole 1.07 +/- 0.08). In acute fracture patients, enhancement of the distal pole was greater than that of the proximal in all cases but one in which the two poles enhanced in a similar fashion (EF: distal 1.99 +/- 0.77, proximal 1.43 +/- 0.99). In chronic fracture patients the enhancement pattern was reversed, as the proximal pole enhanced to a greater degree than the distal with the exception of one case where both poles enhanced equally (EF: distal 1.74 +/- 0.52, proximal 2.64 +/- 0.50). Using a two-tailed non-parametric Mann-Whitney U-test, the difference in enhancement of the proximal poles between the acute and chronic groups was found to be highly significant (P < 0.003). Dynamic contrast-enhanced (fSPGR) MRI demonstrates significant differences in the enhancement patterns of the scaphoid when chronic and acute fractures are compared.

Blunt bowel and mesenteric injury: diagnostic performance of CT signs.

PURPOSE: Our goal was to determine the sensitivity and specificity of various CT signs of blunt bowel and mesenteric injury. METHOD: The CT findings of 31 patients with blunt abdominal trauma were retrospectively assessed by three observers in consensus. All patients had laparotomy within 24 h of CT. The study group consisted of 19 patients with surgically proven bowel and/or mesenteric injury. The control group consisted of 12 traumatized patients who had no bowel or mesenteric injury. The CT signs assessed were presence, location, and extent of intraperitoneal fluid, extraluminal air, bowel wall thickening, bowel wall discontinuity, mesenteric streaking, and mesenteric hematoma. RESULTS: In the 12 cases of bowel injury (9 transmural injury, 3 partial thickness injury), the CT sign of bowel wall thickening had sensitivity of 50% and specificity of 84% and the CT sign of bowel wall discontinuity had sensitivity of 58% and specificity of 95%. Extraluminal air was a specific but relatively insensitive sign of transmural bowel injury (sensitivity 44%, specificity 100%). In the 13 patients with mesenteric injuries, the CT sign of mesenteric hematoma had sensitivity of 54% and specificity of 94%. Isolated mesenteric streaking was a less specific sign of mesenteric injury (sensitivity 77%, specificity 44%). The finding of peritoneal fluid with no visible solid organ injury was a useful sign of bowel or mesenteric injury, occurring in 11 of 19 (58%) study patients and none of the controls (p < 0.001). CONCLUSION: Bowel wall thickening, bowel wall discontinuity, extraluminal air, and mesenteric hematoma are reasonably specific CT signs of bowel and mesenteric injury following blunt abdominal trauma. The presence of a moderate to large volume of intraperitoneal fluid without visible solid organ injury is an important sign of bowel or mesenteric injury.

Osteonecrosis after contact neodymium:yttrium aluminum garnet arthroscopic laser meniscectomy.

OBJECTIVE: The purpose of this report is to describe two cases of osteonecrosis that occurred after arthroscopic meniscectomy with a contact neodymium:yttrium aluminum garnet laser system. The patients developed increasing knee pain and disability 5 months and 6 months after laser meniscectomy. MR imaging showed subchondral osteonecrosis in the femoral condyle and tibial plateau immediately adjacent to the site of laser meniscectomy in both patients. One patient required a total knee replacement to alleviate knee symptoms, and the other patient required a tibial osteotomy and surgical elevation of collapsed tibial articular surface. CONCLUSION: To our knowledge, this complication of laser arthroscopic meniscectomy has not been reported in the radiology literature. The clinical and MR imaging features of this important complication are described and possible causative mechanisms are discussed.