Dose reduction for fluoroscopically guided injections: phantom simulation and patient procedures.

OBJECTIVE: To demonstrate fluoroscopy dose reduction through both simulated injections on a phantom and patient injections. MATERIALS AND METHODS: Our study was IRB-approved and HIPAA-compliant. Simulation on a phantom was used to estimate effective dose, entrance dose, and organ doses for hip joint injections without and with dose minimization technique (DMT). Additionally, 1,094 joint, bursae, and tendon sheath injections performed by three operators in the same fluoroscopy suite were evaluated both before and after application of DMT. Fluoroscopy time (FT), dose, and dose area product (DAP) of injections were compared using unpaired t-tests with P > 0.05 considered statistically significant. RESULTS: For the phantom simulation comparing injections without DMT and with DMT, the total DAP was 191.7 vs 18.7 µGy·m2, and the entrance dose was 10.2 vs 3.6 mGy, respectively. For both men and women, DMT reduces effective dose and organ doses. For all injections, the FT (0.7 to 0.2 min), dose (5.6 to 1.9 mGy), and DAP (56.9 to 19.1 µGy·m2) for all three operators decreased with DMT and remained statistically significant when stratified by the two most common injections, glenohumeral and hip joint injections (P < 0.05). CONCLUSIONS: FT, effective dose, entrance dose, and DAP can be reduced with the use of simple easy-to-learn techniques, which will benefit both the patient and the radiologist.

Giant cystic arachnoid granulations: a rare cause of lytic skull lesions.

Arachnoid granulations provide the pathway for drainage of cerebrospinal fluid from the subarachnoid space into the dural venous sinus system. They frequently produce small, well-defined indentations on the inner table of the calvarium that are easily recognized on radiographic studies and gross examination of the skull. We report a series of four giant cystic arachnoid granulations presenting as large "destructive" osteolytic lesions that required surgical exploration. The cysts were filled with cerebrospinal fluid and were delineated by a thin fibrous wall that contained peripheral clusters of arachnoid cells. We discuss the pathologic and radiographic differential diagnosis of osteolytic skull lesions and present a hypothesis regarding the formation of giant cystic arachnoid granulations.

Knee arthrography. Evolution and current status.

This article explores arthrography of the knee beginning with a brief historical perspective of conventional knee arthrography and culminating in direct and indirect MR arthrography of the knee. This article discusses the advantages of MR arthrography in the radiologic assessment of the postoperative meniscus, abnormalities of articular cartilage, and synovial-based processes.

Magnetic resonance imaging of rheumatoid arthritis.

MR imaging is able to demonstrate both the structural changes that occur in rheumatoid arthritis and the inflammatory changes, including synovial proliferation and joint effusion. MR imaging can demonstrate erosion before it is visible on radiographs. Although MR imaging appears to be very helpful in assessing the severity of rheumatoid arthritis and its response to therapy, the optimal technique for this assessment and the ultimate clinical value of MR imaging have yet to be determined.

MR arthrography: is it worthwhile?

Magnetic resonance (MR) arthrography is possible in any joint in which standard arthrography is performed. The diagnostic potential of this technique is optimized in the assessment of complex anatomical structures and intra-articular abnormalities that are difficult to visualize on conventional MR images. This paper presents the most common applications of MR arthrography in the shoulder, hip, knee, ankle, elbow and wrist, and explores the clinical indications in which MR arthrography adds the greatest benefit compared to standard arthrography and conventional MR imaging. Arthrographic MR images are most valuable in the evaluation of glenoid and acetabular labra, tendons of the rotator cuff, post-operative menisci, osteochondral fractures and loose bodies.

Cartilage and subchondral bone thickness distribution with MR imaging.

RATIONALE AND OBJECTIVES: The authors mapped articular cartilage (AC) and subchondral bone (SB) thicknesses in human acetabula in vitro by using magnetic resonance (MR) imaging and validated AC measurements by using light microscopy. MATERIALS AND METHODS: Left and right acetabula from a deceased patient who had undergone left hemiarthroplasty were imaged with fat-suppressed spoiled gradient-recalled acquisition in the steady state (repetition time = 55 msec, echo time = 15 msec, flip angle = 50 degrees, matrix = 256 x 256, field of view = 8 cm). AC and SB thickness maps were generated from image data by using analytic geometry, which enabled correction for thickness overestimation due to oblique sectioning. Cartilage bone plugs were extracted from the acetabula, and light microscopy was used to validate the thickness measurements obtained with MR imaging. RESULTS: Standard errors between thickness measurements obtained with MR imaging and light microscopy were 0.37 and 0.33 mm for the left and right AC, respectively, which is consistent with the voxel resolution of the MR imaging sequence (0.31 x 0.31 x 0.8 mm). SB thickness of the cartilage plugs could not be reliably measured with light microscopy and, therefore, could not be validated. Contour maps showed that SB thickness gradients were rapid and focal compared with the rather smooth gradients in AC thickness; however, thicker AC was accompanied by thicker SB for left (r2 = .261, P = .0001) and right (r2 = .308, P = .0001) acetabula. Average thickness differences between left and right acetabular AC and SB were 0.13 mm (P = .015) and 0.11 mm (P = .026), respectively. Although it was the operated hip that had thicker articular tissues, the differences were within the pixel resolution (< 0.31 mm). CONCLUSION: AC and SB thickness distribution can be accurately determined by combining noninvasive MR imaging and analytic geometry, which may also provide a means for quantitative, longitudinal assessment of focal AC defects.

Quantification of articular cartilage in the knee with three-dimensional MR imaging.

RATIONALE AND OBJECTIVES: To determine the volume of articular cartilage in cadavers, patients, and healthy volunteers by using a volumetric, fat-suppressed spoiled gradient-recalled signal acquisition in the steady state (SPGR) magnetic resonance (MR) sequence. METHODS: Sagittal MR images were obtained with a fat-suppressed SPGR sequence (repetition time, 52 msec; echo time, 10 msec; 60 degrees flip angle; 3.0-3.5-mm partitions, 256 x 192 matrix, two signals acquired). The cartilaginous surfaces of the tibia, femur, and patella were planimetrically defined with a three-dimensional workstation. A three-dimensional model volume was created by threshold segmenting the cartilage from the adjacent tissues. The volume as calculated by using MR imaging was compared with the actual volume of the cartilage specimens. RESULTS: Observed measurements correlated with actual weight and volume displacement measurements with an accuracy of 82%-99% and linear correlation coefficients of 0.99 (P = 2.5e-15) and 0.99 (P = 4.4e-15). Precision of segmentation in healthy volunteers yielded a coefficient of variation of 0.4% for interobserver variability and 0.3% for intraobserver variability. CONCLUSION: This pilot study suggests that accurate volumetric calculations of knee articular cartilage are possible with currently available MR imaging pulse sequences and a commercially available work station.

CT-guided aspiration in potentially infected total hip replacements complicated by heterotopic bone.

Aspiration of the hip joint in the setting of a potentially infected total hip replacement is occasionally unsuccessful under fluoroscopic guidance because of periarticular heterotopic bone. Of 136 consecutive patients with total hip replacements who were referred to the radiology department for hip aspiration because of suspected infection, successful intraarticular needle placement was achieved in 132 (97%) under fluoroscopic guidance. In four (3%) cases, the attempted aspiration was unsuccessful because heterotopic bone prevented the needle tip from reaching the joint; a second attempt was performed successfully under CT guidance. CT confirmed that the anterior approach was completely blocked by heterotopic bone and that there was a gap in this bone elsewhere through which a needle could be passed into the joint. The increased cost of CT was modest because it was necessary in only a small percentage of patients.

MR arthrography of the shoulder.

Although conventional MR imaging allows direct visualization of major anatomic structures, smaller intraarticular structures, including the glenoid labrum, glenohumeral ligaments, and articular surface of the rotator cuff tendon can be difficult to evaluate in the absence of a joint effusion. The authors review the techniques employed in performing MR arthrography, imaging characteristics of MR arthrography, and diagnostic utilization of the technique. Suggested indications are provided.

MR arthrography of the rotator cuff and labral-ligamentous complex.

In MR imaging of the shoulder, diagnostic success requires the delineation of complex anatomic structures and the demonstration of subtle abnormalities. Magnetic resonance (MR) arthrography extends the capabilities of conventional MR imaging because contrast solution separates intra-articular structures and outlines abnormalities. There are several major contributions of MR arthrography. In assessment of the rotator cuff, arthrographic MR images enable the accurate differentiation of full-thickness tears from other cuff abnormalities, as well as the determination of tendon quality. In shoulders with suspected glenohumeral instability, arthrographic MR images show the locations of labral tears relative to the origins of glenohumeral ligaments. This article illustrates normal arthrographic MR features of the shoulder as well as common pathological disorders of the rotator cuff and labral-ligamentous complex.

A general computing method for spatial cartilage thickness from co-planar MRI.

Techniques for assessing cartilage thickness from planar magnetic resonance (MR) images have traditionally accounted for surface curvature only in the image plane. Many joints, such as the knee and hip, have significant curvature normal (transverse) to the image plane which results in overestimation of in-plane cartilage thickness measurements. We developed a generalized computing method for calculating spatial thickness distribution of joint cartilage from co-planar MR images which accounts for transverse surface curvature. We applied the technique using fat-suppressed SPGR (spoiled gradient recalled in the steady-state) MR images of two human acetabulae and compared the results with a previously validated spherical model of the acetabulum which also accounts for transverse curvature of the cartilage surface. The agreement between the generalized model and validated spherical model was very good for both acetabular specimens (correlation: r = 0.998, p < 0.001; differences: p > 0.63). We conclude that the generalized method is acceptable for computing spatial cartilage thickness distribution of joints with complex geometries, such as the knee.

Re-examining the association of os acromiale with supraspinatus and infraspinatus tears.

PURPOSE: To re-evaluate the relationship between os acromiale and rotator cuff tears. METHODS: We retrospectively analyzed 84 magnetic resonance imaging studies of the shoulder. Forty-two subjects with os acromiale (n = 42; 32 men and ten women, age 25-81 years, mean 47.6 years) were compared with age- and gender-matched subjects with no evidence of os acromiale (controls). Arthroscopy data were available in 19 os acromiale and 12 control subjects. Statistical analyses were performed to determine differences between groups regarding rotator cuff tears affecting the supraspinatus and infraspinatus tendons detected by magnetic resonance imaging and arthroscopy. Analysis of os acromiale type, ossicle synchondrosis edema, acromioclavicular joint degenerative changes and step-off deformity at the synchondrosis were tabulated. RESULTS: No statistically significant difference between the os acromiale and control groups was noted, either on magnetic resonance imaging or arthroscopy, with regard to tears of the supraspinatus (P = 1.000 and 0.981, respectively) and infraspinatus (P = 1.000 and 0.667, respectively) tendons. There was a statistically significant increased number of supraspinatus (P = 0.007) and infraspinatus (P = 0.03) tears in a comparison of subjects with os acromiale and step-off deformity (10/42) vs os acromiale without step-off deformity (32/42). CONCLUSION: The presence of os acromiale may not significantly predispose to supraspinatus and infraspinatus tendon tears. However, subjects with step-off deformity of an os acromiale are at greater risk of rotator cuff tears than are similar subjects without such deformity.

Magnetic resonance imaging in the quantitative assessment of gouty tophi.

Measurements of tophus size can be important in monitoring the course of gout therapy, as tophus resolution is proposed as one measure of success of treatment. This multicentre study assessed the intra- and interreader reproducibility of quantitative tophus volume measurements from magnetic resonance images (MRI) in subjects with palpable gouty tophi. Subjects first underwent radiographic imaging of a selected tophus followed by MRI before and at

Anterior shoulder instability: diagnostic criteria determined from prospective analysis of 121 MR arthrograms.

PURPOSE: To determine magnetic resonance (MR) arthrographic criteria in the diagnosis of anterior glenohumeral instability. MATERIALS AND METHODS: In 121 patients with diagnoses proved surgically, the labrum, glenohumeral ligaments, and capsular insertion types were assessed prospectively with gadolinium-enhanced MR arthrography. Findings were compared in stable and unstable shoulders. RESULTS: Operative results showed 59 normal, 57 torn, and five deficient labra. In 37 unstable shoulders, 31 had discrete inferior labral-ligamentous lesions and six had capsular laxity. MR arthrograms showed labral abnormalities with 92% sensitivity, 92% specificity. Inferior labral-ligamentous lesions enabled prediction of anterior instability with 76% sensitivity (capsular laxity was missed in all shoulders), 98% specificity. Inferior labral-ligamentous abnormalities were strongly associated with unstable shoulders (P << .0001), whereas noninferior labral-ligamentous abnormalities were related to stable shoulders (P = .01). Capsular insertion types showed no significant differences between stable and unstable shoulders (P > .8). CONCLUSION: On MR arthrograms, inferior labral-ligamentous abnormalities were most closely correlated with anterior glenohumeral instability. Capsular insertion sites had no role in the prediction of shoulder instability.

Interactive atlas of joint anatomy on MR images.

We designed and developed an atlas of joint anatomy based on MR images. Using a workstation that consisted of a computer and a videodisc player, each with its own monitor, the program presented complete sets of labeled MR images of the joints by using a variety of common pulse sequences in standard imaging planes. The images were stored on videodisc and were retrieved and displayed under the control of the computer program. The images could be viewed in a self-paced, structured sequence or in any arbitrary, self-directed way. Interactive features included a quiz mode that challenged the user to name the anatomic structures, one at a time. The atlas has been exhibited at national meetings and currently is used in our residency and fellowship training programs.

Vertebral fluid collection associated with vertebral collapse.

OBJECTIVE: Three elderly women with osteoporotic compression fractures of a vertebral body underwent MR imaging because of neurologic signs and symptoms. Atypical fluid collections were shown by MR imaging in all three patients. For histologic characterization of these vertebral fluid collections, CT-guided biopsies and aspirations were done for all three patients. CONCLUSION: After studying the clinical, histologic, and imaging features of these fluid collections associated with vertebral fracture, we suggest that they are most likely associated with underlying avascular necrosis.

MR arthrography of the shoulder: normal intraarticular structures and common abnormalities.

MR imaging with gadopentetate dimeglumine (MR arthrography) is a new technique for evaluating the shoulder. Early clinical experience indicates that MR arthrography improves the visualization of intraarticular structures [1-3]. On T1-weighted images, high-signal contrast solution outlines the low-signal surface of the cuff tendons, the contour of the glenoid labrum, and the course of the glenohumeral ligaments. This essay illustrates the anatomic features of normal glenohumeral structures seen on MR arthrography and common pathologic disorders of the labral-ligamentous complex and rotator cuff.

Labral-ligamentous complex of the shoulder: evaluation with MR arthrography.

PURPOSE: To determine the usefulness of magnetic resonance (MR) arthrography in assessment of the labral-ligamentous complex and test the hypothesis that the inferior glenohumeral ligament (IGHL) is an important anatomic feature of clinical instability. MATERIALS AND METHODS: Forty-eight shoulders with labral diagnoses proved with arthroscopy or open surgery were prospectively examined with MR arthrography after intraarticular injection of gadopentetate dimeglumine. RESULTS: Surgical findings showed that 14 labra were normal, 29 were torn, and six were deficient. (One labrum was torn and deficient in separate locations.) MR arthrographic findings had a diagnostic sensitivity of 91% and specificity of 93%. In 32 patients with proved labral abnormalities, 30 lesions involved the labral-bicipital junction, origins of the glenohumeral ligaments, or both. In 22 of 23 shoulders considered clinically unstable, a labral abnormality involved the origin of the IGHL. CONCLUSION: MR arthrography accurately shows the relationship of labral lesions to the origins of the glenohumeral ligaments and helps in distinction between stable and unstable lesions.

Knee and shoulder fractures: association of fracture detection and marrow edema on MR images with mechanism of injury.

PURPOSE: To assess the value of magnetic resonance (MR) imaging for enabling the classification of fracture mechanisms and to compare marrow edema caused by compressive forces with that caused by tensile forces. MATERIALS AND METHODS: In 62 knees or shoulders, 78 fractures were identified prospectively on MR images or plain radiographs; compressive or tensile forces were determined retrospectively to have caused impaction or distraction fractures, respectively. Edema was measured on T1-weighted images. Frequencies of fracture detection on MR images or plain radiographs were compared. RESULTS: Forty-nine (63%) and 29 (37%) fractures were attributed to compressive and tensile forces, respectively. Edema measured 31 mm +/- 10 in impaction fractures and 2.5 mm +/- 2.4 in distraction fractures (P < .001). MR images and plain radiographs of 63 fractures were compared. On MR images, distraction fractures, including four of seven Segond fractures, were missed more often than impaction fractures (P < .008). Fractures overlooked on MR images were associated with less edema (P < .003). CONCLUSION: On MR images, impaction fractures demonstrate prominent marrow edema, and distraction fractures demonstrate minimal edema. Impaction fractures are more often missed on plain radiographs, and distraction fractures are more often missed on MR images. Segond fractures should be suspected if MR images show lateral capsular ligamentous injury in the knee; in these cases, evaluation with plain radiography is warranted.