P. Lang

High resolution magnetic resonance imaging of the calcaneus: age-related changes in trabecular structure and comparison with dual X-ray absorptiometry measurements

Abstract. A high-resolution magnetic resonance imaging (MRI) protocol, together with specialized image processing techniques, was applied to the quantitative measurement of age-related changes in calcaneal trabecular structure. The reproducibility of the technique was assessed and the annual rates of change for several trabecular structure parameters were measured. The MR-derived trabecular parameters were compared with calcaneal bone mineral density (BMD), measured by dual X-ray absorptiometry (DXA) in the same subjects. Sagittal MR images were acquired at 1.5 T in 23 healthy women (mean age: 49.3 ± 16.6 [SD]), using a three-dimensional gradient echo sequence. Image analysis procedures included internal gray-scale calibration, bone and marrow segmentation, and run-length methods. Three trabecular structure parameters, apparent bone volume (ABV/TV), intercept thickness (I.Th), and intercept separation (I.Sp) were calculated from the MR images. The short- and long-term precision errors (mean %CV) of these measured parameters were in the ranges 1–2% and 3–6%, respectively. Linear regression of the trabecular structure parameters vs. age showed significant correlation: ABV/TV (r2= 33.7%, P < 0.0037), I.Th (r2= 26.6%, P < 0.0118), I.Sp (r2= 28.9%, P < 0.0081). These trends with age were also expressed as annual rates of change: ABV/TV (− 0.52%/year), I.Th (−0.33%/year), and I.Sp (0.59%/year). Linear regression analysis also showed significant correlation between the MR-derived trabecular structure parameters and calcaneal BMD values. Although a larger group of subjects is needed to better define the age-related changes in trabecular structure parameters and their relation to BMD, these preliminary results demonstrate that high-resolution MRI may potentially be useful for the quantitative assessment of trabecular structure.

Pulmonary hypertension in patients with chronic pulmonary thromboembolism: chest radiograph and CT evaluation before and after surgery.

The purpose of this study was to assess the value of morphometric data on conventional radiography and CT predicting the presence and degree of pulmonary hypertension and to assess the reversibility after surgery. On preoperative X-ray films and CT scans of 50 patients with pulmonary hypertension secondary to chronic thromboembolism, we measured the cardiothoracic ratio, basal diameter, length of cardiac contact to sternum, pulmonary trunk, right and left descending pulmonary artery, and the septum angle. These data were correlated with pulmonary arterial pressure. In 14 X-ray patients and 18 CT patients, with follow-up after surgical thromboendarterectomy the reversibility of these changes was assessed. A dilated pulmonary trunk was the most common abnormality (96% each on X-ray and CT). Pulmonary arteries were dilated on X-ray in 40% (right) and 14% (left), and on CT in 92% (right) and 96% (left). The best correlation with mean arterial pressure was found measuring the pulmonary trunk on CT (r = 0.43, p < 0.01). After surgery, reversibility was most significant for the pulmonary trunk on CT (p < 0.0001). In patients with chronic pulmonary embolism, pulmonary hypertension can best be predicted by assessing the diameter of the pulmonary trunk both on X-ray and CT. No close correlation is present between the extent of any parameter and the level of the pulmonary pressure.

Which vertebrae should be assessed using lateral dual-energy X-ray absorptiometry of the lumbar spine

The purpose of this study was to determine precision and diagnostic capability of bone mineral density measurements using lateral dual-energy X-ray absorptiometry (DXA) of the lumbar spine in supine position. Duplicate postero-anterior (PA) and lateral DXA measurements were performed in 60 women. Precision errors of the single vertebral levels using lateral DXA ranged from 3.3% to 4.9%. The combination of all levels improved the precision errors to 2.0%. Paired PA and lateral DXA measurements (Hologic QDR 2000) including the vertebral levels L2 to L4 were performed in 331 postmenopausal women. In 42 women an overlap of L4 by the pelvis was suspected on the lateral DXA images. Vertebral fractures were assessed as a fracture/non-fracture dichotomy. L4 and combinations of vertebrae including L4 showed the best discriminatory capabilities with respect to vertebral fractures in receiver operating characteristic (ROC) analyses,t-tests andZ-scores, with smaller variability of the results when multiple vertebral levels were used. The areas under the ROC curves were 0.662 and 0.639 for lateral and PA measurements of L2 to L4, respectively when all women were included. Excluding the women with pelvic overlap on lateral DXA scans improved the ROC area for lateral scans to 0.686 while that for PA scans remained almost constant (0.641). The differences between PA and lateral measurements were not statistically significant. In 162 women of our study cohort an additional quantitative computed tomography (QCT) measurement of the vertebral levels L2 to L4 was performed and overlapping bony structures at the three levels were studied. Overlapping bony structures were found on QCT slices in 96.9% at the L2 level and in 31.5% at the L3 level. At the L4 level an overlap was found in 5.6% of the women in addition to 31 women in whom L4 overlap had been suspected on DXA images. In total, the level L4 was overlapped in 24.7% of the women. Lateral DXA measurements of the lumbar spine with the patient in supine position are meaningful for diagnosis and follow-up of osteopenia. The inclusion of a maximum number of vertebrae, i.e. L2 to L4 (if L4 is not overlapped by pelvic bone), improves precision and diagnostic capability of the method.

Indirect MR arthrography: techniques and applications

Indirect MR arthrography is a relatively new MR technique improving articular and periarticular contrast. It is achieved by injection of paramagnetic MR contrast media intravenously instead of intra-articular injection as in direct MR arthrography. After the injection exercising the joint results in considerable signal intensity increase within the joint cavity. Fat saturated MR sequences then yield arthrographic images. The method is less invasive than direct MR arthrography and first results showed comparable sensitivities and specificities for rotator cuff and glenoid labrum pathology. In this article the technique, established and potential future indications, drawbacks and limitations of the method are reviewed.

Hematopoietic bone marrow in the adult knee: spin-echo and opposed-phase gradient-echo MR imaging.

Hematopoietic bone marrow in the distal femur of the adult may be mistaken for a pathologic marrow process in magnetic resonance imaging of the knee. We investigated the incidence of hematopoietic marrow in the distal femur in a series of 51 adult patients and compared spin-echo (TR/TE in ms: 500/35, 2000/80) and opposed-phase gradient-echo (0.35 T, TR/TE in ms: 1000/30, θ = 75°) magnetic resonance images. Zones with intermediate to low signal intensity on T1-weighted spinecho and opposed-phase gradient-echo sequences representing hematopoietic marrow within high signal intensity fatty marrow were observed in 18 of the 51 patients. Five patterns of marrow signal reduction were identified; type 0: uniform high signal, i.e., no signal change; type I, focal signal loss; type II, multifocal signal loss without confluence; type III, confluent signal loss; and type IV, complete homogeneous reduction in marrow signal. Opposed-phase gradient-echo sequences demonstrated markedly greater red-yellow marrow contrast than conventional spin-echo sequences. Follow-up studies in three patients using a gradient-echo sequence with TE varying from 10 to 21 ms at 1-ms increments showed a cyclic increase and decrease in red and yellow marrow signal intensity depending on the TE. The contribution of intravoxel chemical shift effects on red-yellow marrow contrast in opposed-phase gradient-echo images was verified by almost complete cancellation of the TE-dependent marrow signal oscillation with use of a chemically selective pulse presaturating the water protons.Hematopoietic marrow in the adult distal femur in the absence of hematologic abnormalities is found primarily in women of menstruating age. It may be residual and may represent a biologic variation in the normal adult pattern of red-yellow marrow distribution. Reconverted red marrow appears to be related to increased erythrocyte demand. Residual and reconverted red marrow should not be mistaken for bone marrow malignancy. Opposed-phase gradient-echo imaging is easily implemented and appears ideally suited to monitor the distribution of hematopoietic marrow as a function of age and erythrocyte demand in vivo.

Shoulder MRI: the subacromial/subdeltoid bursa fat stripe in healthy and pathologic conditions

The MRI appearance of the subacromial/subdeltoid (SA-SD) bursa is described here in both healthy and pathological conditions. Based on one case of rotator cuff tear and intrabursal fluid outlined by two adjacent fat stripes we reviewed 20 shoulder MR examinations to define the normal and abnormal appearance of the peribursal fat. We found four pathological patterns: lateral displacement, tear-drop configuration, obliteration and double fat stripe.

Three-dimensional reconstruction - Part I: Applications and techniques

Three-dimensional reconstruction of cross-sectional imaging data is gaining increasing acceptance by clinicians. Some applications have been introduced in routine imaging. These applications are summarised and discussed. In order to yield a three-dimensional rendered image several steps such as preprocessing, segmentation, interpolation and rendering are necessary, and various modifications of each step are possible. The technical possibilities in each step are summarised and described.

Three-dimensional reconstruction: Part II: Optimisation of segmentation and rendering of MRI

We tried to improve the basic three-dimensional reconstruction technique by comparing preprocessing, segmentation, shading and rendering techniques in 15 examples of MR investigations of the knee joint. We conclude that signal-normalising, combined threshold and tracking segmentation, grey-level-gradient shading, and combined surface and volume rendering (i. e. hybrid rendering) are the methods of choice for the three-dimensional reconstruction process.