Imaging articular cartilage defects with 3D fat-suppressed echo planar imaging: comparison with conventional 3D fat-suppressed gradient echo sequence and correlation with histology

PURPOSE

Our goal was to shorten examination time in articular cartilage imaging by use of a recently developed 3D multishot echo planar imaging (EPI) sequence with fat suppression (FS). We performed comparisons with 3D FS GE sequence using histology as the standard of reference.

METHOD

Twenty patients with severe gonarthrosis who were scheduled for total knee replacement underwent MRI prior to surgery. Hyaline cartilage was imaged with a 3D FS EPI and a 3D FS GE sequence. Signal intensities of articular structures were measured, and contrast-to-noise (C/N) ratios were calculated. Each knee was subdivided into 10 cartilage surfaces. From a total of 188 (3D EPI sequence) and 198 (3D GE sequence) cartilage surfaces, 73 and 79 histologic specimens could be obtained and analyzed. MR grading of cartilage lesions on both sequences was based on a five grade classification scheme and compared with histologic grading.

RESULTS

The 3D FS EPI sequence provided a high C/N ratio between cartilage and subchondral bone similar to that of the 3D FS GE sequence. The C/N ratio between cartilage and effusion was significantly lower on the 3D EPI sequence due to higher signal intensity of fluid. MR grading of cartilage abnormalities using 3D FS EPI and 3D GE sequence correlated well with histologic grading. 3D FS EPI sequence agreed within one grade in 69 of 73 (94.5%) histologically proven cartilage lesions and 3D FS GE sequence agreed within one grade in 76 of 79 (96.2%) lesions. The gradings were identical in 38 of 73 (52.1%) and in 46 of 79 (58.3%) cases, respectively. The difference between the sensitivities was statistically not significant.

CONCLUSION

The 3D FS EPI sequence is comparable with the 3D FS GE sequence in the noninvasive evaluation of advanced cartilage abnormalities but reduces scan time by a factor of 4.

MR-guided joint puncture and real-time MR-assisted contrast media application

OBJECTIVE

To develop, in MR arthrography of the shoulder joint, an MR-guided technique for localizing the needle puncture and confirming the intracapsular needle-tip position by visualization of the contrast media inflow.

MATERIAL AND METHODS

Three unfixed human shoulder specimens were examined on a 1.0 T MR unit. On the basis of MR-compatible markers, the optimal entrance point for puncturing the joint was determined. The precise localization of the needle tip (MR-compatible 0.7-mm needle) in the shoulder joint was determined with rapid localizer GRE sequences in 2 orthogonal planes. To confirm the intracapsular position of the needle tip, diluted Gd-DTPA was applied via a long connecting tube and contrast medium inflow into the joint space was controlled on an LCD screen in real-time MR imaging (local-look technique).

RESULTS

MR-compatible markers on the skin allowed the rapid determination of the optimal entrance point for needle puncture. An adequate localization of the intra-articular needle-tip position was possible in all specimens although significant artifacts were present on rapid localizer GRE sequences which resulted in an increase in the apparent width of the needle shaft. Real-time MR imaging of the contrast medium inflow was made possible by the local-look technique and LCD screen on the MR unit and this allowed confirmation of the intracapsular position.

CONCLUSION

In MR arthrography of the shoulder, an MR-guided technique in conjunction with the LCD screen and real-time MR imaging would seem to be a practical alternative to conventional fluoroscopic guidance.

[MRI in radiologically occult scaphoid fractures. Initial experiences with 1.0 Tesla (whole body-middle field equipment) versus 0.2 Tesla (dedicated low-field equipment)]

The study was performed to determine the diagnostic value of different MR systems and field strengths in patients with occult scaphoid and wrist fractures. Twelve patients with clinical suspicion of a scaphoid fracture but normal plain radiographs were examined by MRI. A dedicated 0.2-T unit (Esaote) and a 1.0-T unit (NT10, Philips) were used. Coronal T1W-SE, STIR, and T2*W-GE sequences were obtained with both systems. Images were evaluated for a bone marrow abnormality, a trabecular or cortical fracture line, and were compared to the 6-week follow-up radiographs. Seven wrist fractures were found at 0.2 T and 1.0 T, proven in the follow-up radiographs. A bone marrow abnormality was present in all seven fractures on both systems. Trabecular and cortical fracture lines were visualized at 0.2 T in four cases and at 1.0 T in seven cases. Low-field MR imaging at 0.2 T and mid-field MR imaging at 1.0 T seem to be equivalent in the diagnosis of a fracture in radiographically occult scaphoid and wrist fractures. In the visualization of fracture details, important for therapeutic and prognostic considerations, 1.0 T seems to be superior.

[Comparison of diagnostic sensitivity in meniscus diagnosis of MRI examinations with a 0.2 T low-field and a 1.5 T high field system]

The aim of this study was to evaluate the reliability of a low field strength MRI unit (0.2 T; Esaote, Biomedica) and a high field strength MRI unit (1.5 T; Siemens) in detecting meniscal lesions. Twenty patients were investigated on a 0.2-T low-field MRI unit and a 1.5-T high-field MRI unit for meniscal lesions. Evaluation was performed of four meniscal compartments (anterior and posterior medial and lateral meniscus), for a total of 80 observations. The reliability of diagnosis was ranked qualitatively on a three-point scale. Investigations of the high-field MRI unit revealed a meniscal tear in 6 patients and ruled out a tear in 14 patients. Evaluation of individual meniscal compartments revealed diagnosis with high confidence in 58 observations and with moderate confidence in 22 observations. Investigations of the low-field MRI unit revealed a meniscal tear in 5 patients and ruled out tears in 15 patients. Evaluation of individual meniscal compartments revealed diagnosis with high confidence in 39 observations, with moderate confidence in 38 observations, and with low confidence in 3 observations. The diagnosis in high- and low-field images was identical in 98.7% of cases; in one patient observations from the high-field unit changed the therapeutic management. Diagnostic reliability was significantly higher with high-field strength MR imaging. Low field strength MR imaging shows comparatively high diagnostic accuracy for meniscal lesions compared to high field strength imaging; however, we demonstrated a significantly higher confidence in diagnosis with high-field MR imaging.

[MRI on low-field tomography systems (0.2 Tesla). A quantitative comparison with equipment of medium-field strength (1.0 Tesla)]

AIM OF THE STUDY

Using phantom studies, a dedicated low-field MR system with 0.2 T and a whole-body MR-scanner with 1.0 T were compared.

METHODS

A spin-echo sequence was performed on the 0.2-T MR unit using the knee coil and on the 1.0-T MR unit with the head coil. In a water-filled phantom, signal-to-noise ratios (SNR) were calculated and contrast measurements on gels with well-defined relaxation times were obtained and compared to nominal relaxation times. Measurements of T1 and T2 relaxation times on the low-field system were compared to the 1.0-T unit. As a parameter for geometrical image quality, magnetic field distortions were calculated. In theory, influence of field strength and and receiver bandwidth on the minimal echo time and on chemical shift artifacts were calculated.

RESULTS

The SNR was 63.2 on the 0.2-T and 179.6 on the 1.0-T MR unit (difference factor 3, against a theoretical difference of 5-16). Relaxation times on the low-field system were significantly (around 40-50%) lower. Measurements of contrast were similar on both systems. On the low-field system geometrical distortions of several pixels were recorded. The minimal echo time on the low-field system was 21.3 ms with the low receiver bandwidth and 4.3 ms on the 1.0-T MR unit. The amount of chemical shift artefacts was the same on both systems.

DISCUSSION

On low-field MR systems SNR is markedly improved by small read-out gradients and a low receiver bandwidth (factor 3 vs 5-16 in comparison with the 1.0-T MR unit). However, an optimal homogeneous magnetic field is required, since inhomogeneities may create severe geometrical distortion.

GRASE: ultra-fast turbo gradient spin-echo sequence. A new approach to fast MR imaging of the musculoskeletal system

PURPOSE

Ultra-fast gradient and spin-echo (GRASE) imaging is a hybrid of turbo spin-echo (TSE) and echo-planar imaging (EPI). One scan consists of several spin echoes (SEs) (turbo factor, TF), each of which consists of a number of gradient echoes (EPI factor, EF). The aim of our study was to evaluate different combinations of TF and EF in GRASE imaging and to test its usefulness in musculoskeletal imaging.

MATERIAL AND METHODS

On a 1.0 T MR unit, 11 GRASE sequences with different combinations of TF and EF (TR/TE 2150/120 ms) were evaluated in phantom studies with respect to signal-to-noise (S/N) ratio, nonuniformity of images, and geometrical distortion. From this study, the optimal GRASE-sequence was applied to 25 patients with different joint pathologies and compared to a T2-weighted TSE sequence (TR/TE 2855/130 ms). Lesion visualization, conspicuity, overall image quality, and artifacts were qualitatively analyzed by two observers independently of each other.

RESULTS

With respect to S/N ratio, signal nonuniformity, and geometrical distortion, the GRASE sequence with TF/EF 7/3 (S/N 47; signal nonuniformity 11.7%; distortion 1 pixel) proved to be superior to the other GRASE sequences within a scanning time of less than 120 s. In a clinical study, the GRASE sequence proved superior to T2-weighted TSE (without fat suppression) in the visualization of bone-marrow and soft-tissue lesions (p < 0.001) and ligamentous injuries, although the image quality was inferior.

Impact of spinal degenerative changes on the evaluation of bone mineral density with dual energy X-ray absorptiometry (DXA)

The purpose of this study is to evaluate degenerative factors in a postmenopausal patient group and differentiate the influence on bone mineral density (BMD) measurements by dual-energy X-ray absorptiometry (DXA). The patients and methods included an investigation of 144 postmenopausal women (mean 63.3 years) with PA-DXA of the spine. Degenerative factors (osteophytes, osteochondrosis, scoliosis, and vascular calcification) were evaluated from plain lumbar radiographs, their estimated probability was analyzed as a function of age, and their influence on BMD measured by PA-DXA was determined. The results of the study revealed osteophytes in 45.8%, vascular calcifications in 24.3%, scoliosis in 22.2%, osteochondrosis in 21.5%. The estimated probability for degenerative factors increased from 35 to 80% in the 55- to 70- year age group. Osteophytes and osteochondrosis were associated with up to a 14% increase in BMD values (P < 0.001). Vascular calcifications showed a positive trend, whereas scoliosis did not show a discernible influence.We concluded that degenerative factors, except for scoliosis, showed an influence on BMD as measured by DXA. Their prevalence increased rapidly between 55 and 70 years of age. Interpretation of PA-DXA spine data for subjects of or above this age range should be complemented by plain film radiographs.

Mammography in women undergoing hormone replacement therapy. Possible effects revealed at routine examination

PURPOSE

A retrospective study of screen-film mammographs was performed in 960 postmenopausal women to evaluate the possible effects of hormonal replacement therapy on the breast parenchymal pattern.

MATERIAL AND METHODS

Screen-film mammographs of 754 women (mean age 51.4 years) who had undergone hormonal replacement therapy (estrogen, gestagen; mean duration 2.4 years) were compared with findings in 206 women who had not received hormonal replacement therapy (mean age 52.3 years). Mastopathic changes were analyzed according to a 4-grade scale and the incidence of circumscribed lesions (such as fibroadenomas, cysts and malignancies) was further evaluated.

RESULTS

In the treated women we found moderate mastopathic changes in 47.2%, intermediate changes in 2.4%, and extensive proliferations in 0.7%. For the untreated women the corresponding figures were 33.5%, 4.8%, and 1.4%. In the treated patients fibroadenomas were apparent in 3.9%, cystic lesions in 3.3%, and malignant lesions in 1.4%. In the untreated women fibroadenomas were evident in 11.6%, cystic lesions in 7.2%, and malignant lesions in 2.4%.

CONCLUSION

Mastopathic changes might increase under hormonal replacement therapy. However, the higher incidence of circumscribed lesions in the untreated women might be due to the higher number of symptomatic women who sought examination. We also speculate as to whether the increased density of the breast parenchyma in the treated women might cause a higher number of mammographically undedectable lesions.

Influence of osteophytic size on bone mineral density measured by dual X-ray absorptiometry

PURPOSE

To quantify the relationship between individual osteophytic size and measured bone mineral density (BMD) of the lumbar spine by dual x-ray absorptiometry (DXA). Further, to evaluate the possible consequences of this relationship for the management of DXA measurements in postmenopausal patients.

MATERIAL AND METHODS

In 142 postmenopausal women (mean age 61.8 +/- 8.9 years), plain radiographs of the lumbar spine were evaluated and graded according to evidence and size of osteophytes. The BMD (g/cm2) and Z-score (deviation of BMD from an age-matched population, %) of each vertebral body was determined by DXA. The effects of the individual osteophytic size on BMD measurements were analyzed by using analysis of variance followed by a multiple test procedure.

RESULTS

The presence of osteophytes resulted in a significant increase in BMD of L1 through L4. The increase in relation to an osteophytic size of about 10 mm was: in L1 5.7%, in L2 6.8%, in L3 4.4% and in L4 3.5%. Increases were significantly higher for an osteophytic size of 10-20 mm (L1 23.1%, L2 13.0%, L3 13.4%, and L4 16.3%) and of > 20 mm (L1 21.4%, L2 22.4%, L3 21.1% and L4 4.1%).

CONCLUSION

Our results indicate a nonlinear increase of measured BMD with increasing osteophytic size. These effects should be considered in routine examination and patient management.

[MR arthrography of the shoulder joint in a postoperative patient sample]

Indications of MR arthrography were analyzed in this prospective study. The aim was to evaluate possible advantages over conventional MRI, establish diagnostic criteria and to analyze its meaning further for the therapeutic management of postoperative patients. MR arthrography was performed in eight patients who had undergone surgical repair of rotator cuff lesions (modified Neer acromioplasty) and in six patients who had undergone arthroscopic therapy of recurrent unidirectional dislocation of the shoulder by combined arthroscopic intra- and extracapsular repair. MR investigations were performed before and after application of a contrast solution (2 mmol Gd-DTPA). All patients suffered from chronic postoperative pain. In patients with rotator cuff lesions, a partial tear could be verified in one patient and excluded in all others. In patients after arthroscopic therapy by combined intra- and extracapsular repair, a radiologically patulous-appearing capsule correlated with clinically recurrent dislocations. In all other patients diagnostic criteria, such as distribution of the intra-articular contrast solution, proliferation of scar tissue, nodular appearance of the glenohumeral ligaments and capsule thickness, correlated with a regular postoperative status. MR arthrography of the shoulder represents a promising method in the evaluation of the postoperative shoulder. It might further improve the evaluation of reactive capsule alterations, scar tissue proliferation, and the labroligamentous complex, as well as the ability to differentiate partial and complete rerupture from degenerative changes of the rotator cuff.

MRI of microadenomas in patients with hyperprolactinaemia

MRI is a sensitive tool for the investigation of pituitary microadenomas but cannot be used as a screening investigation. To establish a strategy for the use of MRI in patients with hyperprolactinaemia we investigated 74 women with serum prolactin levels above 52 ng/ml for the presence of microadenomas. We examined 55 premenopausal and 19 postmenopausal women, using a 1.5 T unit. We used T1-weighted spin-echo sequences, with coronal and sagittal images before and after intravenous gadolinium. We found microadenomas in 38 patients (51.3%), macroadenomas in 6 (8.1%) and an infundibular glioma in 1;29 patients had a normal pituitary gland (39.2%). The size of the adenomas was related to the prolactin level, and the mean level in patients with MRI evidence of adenomas was higher than in patients without microadenomas (155.72 +/- 131.01 ng/ml versus 110.14 +/- 80.86 ng/ml). The probability of the presence of an adenoma increased with rising serum prolactin levels. We suggest MRI in patients with prolactin levels more than 100 ng/ml. In patients on oestrogen therapy MRI should be performed with only slightly elevated prolactin levels. Evidence of a microadenoma should be considered in planning further therapy, especially concerning the use of hormone replacement therapy or of bromocriptine.

[Ultrasound morphology of the Achilles tendon and differential diagnosis]

AIM

To correlate sonographic findings and clinical disorders of the Achilles tendon, considering newer aspects of their etiology and pathogenesis.

METHOD

In a retrospective cross-sectional study the sonographic findings in 52 patients with tendonitis, heel swelling, or suspected rupture were analysed and correlated with the final diagnosis. Tendon lesions due to lipid storage diseases or rheumatic diseases were analysed on the basis of reports in the literature.

RESULTS

Ultrasound abnormalities were found in 41 of the 52 symptomatic patients (40 degenerative changes of the tendon and/or the peritendinous tissue, 1 inflammatory rheumatologic process, 1 metabolic disorder, 8 ruptures, 2 congenital or developmental abnormalities). Ultrasound signs were not specific for each of the diagnoses but typical combinations of distinctive signs together with clinical findings led to the correct diagnoses.

CONCLUSION

Patients with suspected lesions of the Achilles tendon should undergo an ultrasound investigation both to promote the exact diagnosis and to define the extent of the disease.

[MRI-guided MRI arthrography of the shoulder]

PURPOSE

To develop an MR-guided technique for joint puncture in MR arthrography of the shoulder and to confirm the intracapsular position of the needle tip by visualization of the flow of contrast media into the joint.

MATERIALS AND METHODS

Three unfixed human shoulder joint specimens were examined on a LOT unit. The optimal point of entrance and depth for joint puncture were estimated by means of MR-compatible markers on the skin. Needle orientation and localization of the needle tip (MR-compatible 22-gauge needle) in the shoulder joint were monitored by rapid localizer gradient-echo sequences in two or thogonal planes. To confirm the intracapsular position of the needle tip, diluted gadolinium-DTPA was administered via a long connecting tube and the flow of contrast media into the joint was viewed directly on an LCD screen using real-time MR imaging (local look technique).

RESULTS

The MR-compatible markers on the skin allowed determination of the optimal point of entrance and estimation of the depth for joint puncture. Passive visualization of the MR-compatible needle due to spin dephasing and signal loss provided adequate localization of the intra-articular needle tip position in all specimens, although significant artefacts were present on rapid localizer gradient-echo sequences with an increase in width of the apparent needle shaft. Real-time MR imaging of the flow of contrast media was possible using the local look technique and the LCD screen of the MR unit and allowed confirmation of the intracapsular position.

CONCLUSION

MR-guided joint puncture and real-time MR-assisted contrast media application results in improved MR-arthrography and may replace conventional fluoroscopic guidance.

[Primary chronic polyarthritis of the knee joint]

Rheumatoid arthritis is a chronic, multisystemic disease. The characteristic feature is persistent inflammatory synovitis. The knee joint is commonly involved with synovial hypertrophy, chronic effusion, and frequently ligamentous laxity. Pain and swelling behind the knee may be caused by extension of inflamed synovium into the popliteal space (Baker's cyst). Plain radiographs of the knee joint remain the basic radiological procedure, although early in the disease they might not provide significant changes. Sonography sufficiently reveals synovial fluid and Baker cysts, but cannot be recommended for evaluation of synovial proliferations or pannus formation. Computer tomography has only limited indications and may be used for the evaluation of subtle erosive lesions or the quantitation of osteoporotic changes. Magnetic resonance imaging has shown excellent visualization of cartilage, fluid, synovium and soft tissues and is the method of choice for the demonstration of early affection and the evaluation of pannus activity and therapy control. With administration of contrast agents (gadolinium), dynamic studies may demonstrate inflammatory activity. Modern MR sequences, such as T1 SE "fat sat" or magnetization transfer, further improve the discrimination of cartilage, pannus and synovial fluid.

Effects of umbilical arterial catheterization on mesenteric hemodynamics

Impairment of mesenteric blood flow due to the use of umbilical artery catheters (UAC) may increase the risk of necrotizing enterocolitis (NEC) in newborn infants. We used Duplex Doppler sonography to investigate the degree of vessel obstruction due to UAC and their effect on visceral hemodynamics in 12 newborn infants. Ultrasonography was performed before and immediately after removal of the UAC, which was positioned above the ostia of the celiac and superior mesenteric arteries (SMA). Vessel diameter, peak systolic blood flow velocity (PSFV), end diastolic blood flow velocity (EDFV), and Pourcelot's resistance index (RI) were measured in the celiac trunk and the SMA within 1 cm of their origins. Removal of the UAC led to a significant increase in mean PSFV (celiac trunk: 50 cm/s +/- 15 vs 62 cm/s +/- 0.22, P < 0.05; SMA: 52 cm/s +/- 0.17 vs 72 cm/s +/- 0.21, P < 0.05). RI increased from 0.7 +/- 0.14 to 0.74 +/- 0.13 and from 0.73 +/- 0.1 to 0.76 +/- 0.13 for the celiac trunk and SMA, respectively. The EDFV and vessel diameters did not change significantly after UAC removal. Our results suggest that UAC cause a decrease in mesenteric blood flow. Therefore, their use in hemodynamically unstable neonates or in those with gastrointestinal disease should be very carefully considered.

Infratentorial brain maturation: a comparison of MRI at 0.5 and 1.5T

Our purpose was to establish parameters for normal infratentorial brain maturation at 0.5 and 1.5 T and to evaluate the field strength criteria for the assessment of infratentorial brain maturation with MRI. We examined 27 children with normal psychomotor development (3 days to 24 months) with a 1.5 T system and 22 (4 days to 29 months) with a 0.5 T system; standard T2-weighted spin-echo sequences (TR/TE 2500/90 ms at 1.5 T and TR/TE 2200/90 ms at 0.5 T) were obtained. The signal intensity of infratentorial anatomical structures compared to their surroundings was classified as high, isointense or low by three neuroradiologists. For anatomical structures with age-related contrast changes, the time of these changes was determined statistically for the 0.5 T and 1.5 T system independently. The delineation of the structures without age-related contrast changes at the two field strengths was compared using a chi 2 test. Age-related contrast changed were found in the same anatomical structures ("marker sites") at 0.5 and 1.5 T. Generally, these changes were apparent in larger structures (pons, middle cerebellar peduncles, medulla, cerebellar folia, red nuclei, cerebral peduncles), with only slight field-strength-dependent differences in the time of the contrast changes. Contrast changes from high to isointense signal were observed slightly earlier at 0.5 T and changes from isointense to low signal slightly later at 0.5 T. The delineation of the smaller anatomical structures was significantly better at 1.5 T but these structures did not show age-related contrast changes. The differences in the assessment of infratentorial brain maturation between 0.5 and 1.5 T can be attributed to a lower signal-to-noise ratio at lower magnetic field strengths. These differences do not complicate temporal classification of the stage of infratentorial brain maturation using the same "marker sites" and the same temporal criteria at 0.5 or 1.5 T. However, higher field strengths are preferable for the assessment of smaller structures with physiological signal differences; this may imply better detection of small lesions at higher field strengths.

Prevalence of acquired cystic kidney disease and tumors in native kidneys of renal transplant recipients: a prospective US study

PURPOSE

To determine the prevalence of acquired cystic kidney disease (ACKD) and renal neoplasms in the native kidneys of renal transplant recipients.

MATERIALS AND METHODS

The ultrasound (US) scans in 385 renal allograft recipients were prospectively studied. In addition, 65 patients with ACKD underwent two additional US examinations on different days to assess intra- and interobserver variability with regard to the number of cysts and their diameter.

RESULTS

ACKD was present in 96 of 385 patients. Patients with ACKD were significantly older than patients without ACKD, had undergone hemodialysis for a longer period, and were predominantly men. There was no significant difference in the time with functioning graft. Renal cell carcinoma (RCC) was diagnosed in six patients at histologic examination. Of these six patients, five had evidence of ACKD.

CONCLUSION

The frequency of ACKD increases with the duration of hemodialysis. The risk for the development of ACKD is increased in men and older patients. The malignant potential of ACKD persists after renal transplantation.

Colour-coded Doppler sonography of common carotid artery dissection

Colour Doppler sonography allowed noninvasive confirmation of bilateral common carotid artery dissection in a patient with previous aortic dissection. It also cast light on the pathophysiology.