Siegfried Trattnig

Diffusion-weighted MR for Differentiation of Breast Lesions at 3.0 T: How Does Selection of Diffusion Protocols Affect Diagnosis?

PURPOSE To compare the diagnostic quality of diffusion-weighted (DW) imaging schemes with regard to apparent diffusion coefficient (ADC) accuracy, ADC precision, and DW imaging contrast-to-noise ratio (CNR) for different types of lesions and breast tissue. MATERIALS AND METHODS Institutional review board approval and written, informed consent were obtained. Fifty-one patients with histopathologic correlation or follow-up performed with a 3.0-T MR imager were included in this study. There were 112 regions of interest drawn in 24 malignant, 17 benign, 20 cystic, and 51 normal tissue regions. ADC maps were calculated for combinations of 10 b values (range, 0-1250 sec/mm(2)). Differences in ADC among tissue types were evaluated. The CNRs of lesions at DW imaging were compared for all b values. A repeated-measures analysis of variance was used to assess lesion differentiation. RESULTS ADCs calculated from b values of 50 and 850 sec/mm(2) were 0.99 x 10(-3) mm(2)/sec +/- 0.18 (standard deviation), 1.47 x 10(-3) mm(2)/sec +/- 0.21, 1.85 x 10(-3) mm(2)/sec +/- 0.22, and 2.64 x 10(-3) mm(2)/sec +/- 0.30 for malignant, benign, normal, and cystic tissues, respectively. An ADC threshold level of 1.25 x 10(-3) mm(2)/sec allowed discrimination between malignant and benign lesions with a diagnostic accuracy of 95% (P < .001). ADC calculations performed with multiple b values were not significantly more precise than those performed with only two. We found an overestimation of ADC for maximum b values of up to 1000 sec/mm(2). The best CNR for tumors was identified at 850 sec/mm(2). CONCLUSION Optimum ADC determination and DW imaging quality at 3.0 T was found with a combined b value protocol of 50 and 850 sec/mm(2). This provided a high accuracy for differentiation of benign and malignant breast tumors.

Anatomy, biochemistry, and physiology of articular cartilage.

Huber M, Trattnig S, Lintner F. Anatomy, biochemistry, and physiology of articular cartilage. Invest Radiol 2000;35:573–580. ABSTRACT.Articular cartilage serves as a load-bearing elastic material that is responsible for the frictionless movement of the surfaces of articulating joints. Its ability to undergo reversible deformation depends on its structural organization, including the specific arrangement of the matrix macromolecules and the chondrocytes. Interactions between the matrix and chondrocytes are responsible for the biological and mechanical properties of articular cartilage and enable it to respond by effecting a balance between anabolism and catabolism as well as continual internal remodeling. Age-related changes in the function of chondrocytes may contribute to the initiation and progression of osteoarthritis.

The role of relaxation times in monitoring proteoglycan depletion in articular cartilage.

Various proton relaxation times (T2, T1ρ, and gadolinium‐diethylene triamine pentaacetic acid [Gd‐DTPA]‐enhanced T1) were measured in articular cartilage in vitro at 3 T to assess their role in visualizing proteoglycan depletion. Cartilage‐bone specimens were obtained from patients who underwent total joint replacement and got a double dose of Gd‐DTPA 2 hours prior surgery. In these specimens, regions of mechanically undamaged cartilage having a decreased content of proteoglycans showed about 15% lower T1 values compared with apparently normal cartilaginous tissue. The expected increase of the T2 relaxation time was not observed in these regions. On the other hand, the T2 and, to a lower degree, T1 relaxation times were found to be increased in regions of cartilage fibrillation. The T1ρ relaxation times obtained were slightly longer than the corresponding T2 values, but both parameters showed almost identical spatial distributions. J. Magn. Reson. Imaging 1999;10:497–502.

Cartilage T2 Assessment at 3-T MR Imaging: In Vivo Differentiation of Normal Hyaline Cartilage from Reparative Tissue after Two Cartilage Repair Procedures—Initial Experience

PURPOSE To prospectively compare cartilage T2 values after microfracture therapy (MFX) and matrix-associated autologous chondrocyte transplantation (MACT) repair procedures. MATERIALS AND METHODS The study had institutional review board approval by the ethics committee of the Medical University of Vienna; informed consent was obtained. Twenty patients who underwent MFX or MACT (10 in each group) were enrolled. For comparability, patients of each group were matched by mean age (MFX, 40.0 years +/- 15.4 [standard deviation]; MACT, 41.0 years +/- 8.9) and postoperative interval (MFX, 28.6 months +/- 5.2; MACT, 27.4 months +/- 13.1). Magnetic resonance (MR) imaging was performed with a 3-T MR imager, and T2 maps were calculated from a multiecho spin-echo measurement. Global, as well as zonal, quantitative T2 values were calculated within the cartilage repair area and within cartilage sites determined to be morphologically normal articular cartilage. Additionally, with consideration of the zonal organization, global regions of interest were subdivided into deep and superficial areas. Differences between cartilage sites and groups were calculated by using a three-way analysis of variance. RESULTS Quantitative T2 assessment of normal native hyaline cartilage showed similar results for all patients and a significant trend of increasing T2 values from deep to superficial zones (P < .05). In cartilage repair areas after MFX, global mean T2 was significantly reduced (P < .05), whereas after MACT, mean T2 was not reduced (P > or = .05). For zonal variation, repair tissue after MFX showed no significant trend between different depths (P > or = .05), in contrast to repair tissue after MACT, in which a significant increase from deep to superficial zones (P < .05) could be observed. CONCLUSION Quantitative T2 mapping seems to reflect differences in repair tissues formed after two surgical cartilage repair procedures. (c) RSNA, 2008.

MR imaging of osteochondral grafts and autologous chondrocyte implantation.

Surgical articular cartilage repair therapies for cartilage defects such as osteochondral autograft transfer, autologous chondrocyte implantation (ACI) or matrix associated autologous chondrocyte transplantation (MACT) are becoming more common. MRI has become the method of choice for non-invasive follow-up of patients after cartilage repair surgery. It should be performed with cartilage sensitive sequences, including fat-suppressed proton density-weighted T2 fast spin-echo (PD/T2-FSE) and three-dimensional gradient-echo (3D GRE) sequences, which provide good signal-to-noise and contrast-to-noise ratios. A thorough magnetic resonance (MR)-based assessment of cartilage repair tissue includes evaluations of defect filling, the surface and structure of repair tissue, the signal intensity of repair tissue and the subchondral bone status. Furthermore, in osteochondral autografts surface congruity, osseous incorporation and the donor site should be assessed. High spatial resolution is mandatory and can be achieved either by using a surface coil with a 1.5-T scanner or with a knee coil at 3 T; it is particularly important for assessing graft morphology and integration. Moreover, MR imaging facilitates assessment of complications including periosteal hypertrophy, delamination, adhesions, surface incongruence and reactive changes such as effusions and synovitis. Ongoing developments include isotropic 3D sequences, for improved morphological analysis, and in vivo biochemical imaging such as dGEMRIC, T2 mapping and diffusion-weighted imaging, which make functional analysis of cartilage possible.

Three‐dimensional delayed gadolinium‐enhanced MRI of cartilage (dGEMRIC) for in vivo evaluation of reparative cartilage after matrix‐associated autologous chondrocyte transplantation at 3.0T: Preliminary results

To use a 3D gradient‐echo (GRE) sequence with two flip angles for delayed gadolinium‐enhanced MRI of cartilage (dGEMRIC) to evaluate relative glycosaminoglycan content of repair tissue after matrix‐associated autologous chondrocyte transplantation (MACT).

Cartilage Quality Assessment by Using Glycosaminoglycan Chemical Exchange Saturation Transfer and 23Na MR Imaging at 7 T

PURPOSE To compare a glycosaminoglycan chemical exchange saturation transfer (gagCEST) imaging method, which enables sampling of the water signal as a function of the presaturation offset (z-spectrum) at 13 points in clinically feasible imaging times, with sodium 23 ((23)Na) magnetic resonance (MR) imaging in patients after cartilage repair surgery (matrix-associated autologous chondrocyte transplantation and microfracture therapy). MATERIALS AND METHODS One female patient (67.3 years), and 11 male patients (median age, 28.8 years; interquartile range [IQR], 24.6-32.3 years) were examined with a 7-T whole-body system, with approval of the local ethics committee after written informed consent was obtained. A modified three-dimensional gradient-echo sequence and a 28-channel knee coil were used for gagCEST imaging. (23)Na imaging was performed with a circularly polarized knee coil by using a modified gradient-echo sequence. Statistical analysis of differences and Spearman correlation were applied. RESULTS The median of asymmetries in gagCEST z-spectra summed over all offsets from 0 to 1.3 ppm was 7.99% (IQR, 6.33%-8.79%) in native cartilage and 5.13% (IQR, 2.64%-6.34%) in repair tissue. A strong correlation (r = 0.701; 95% confidence interval: 0.21, 0.91) was found between ratios of signal intensity from native cartilage to signal intensity from repair tissue obtained with gagCEST or (23)Na imaging. The median of dimensionless ratios between native cartilage and repair tissue was 1.28 (IQR, 1.20-1.58) for gagCEST and 1.26 (IQR, 1.21-1.48) for (23)Na MR imaging. CONCLUSION The high correlation between the introduced gagCEST method and (23)Na imaging implies that gagCEST is a potentially useful biomarker for glycosaminoglycans.

MRI visualization of proteoglycan depletion in articular cartilage via intravenous administration of Gd-DTPA.

The effect of intravenous administration of gadolinium diethylenetriamine-pentaacetic acid (Gd-DTPA) on MR images was studied in vitro, using pathologic osteochondral specimens removed during surgery for total endoprosthesis, and in vivo, on a group of volunteers. In ex vivo specimens, lesions of different shape having lower T1 were detected which corresponded to areas with depleted proteoglycans found histologically. In vivo experiments on young volunteers showed that the time course of cartilage enhancement was different for different anatomies. The time for maximum enhancement ranged from 45 min for the ventral femoral condyle to 270 min for patellar cartilage.

Advances in Imaging of Osteoarthritis and Cartilage

Osteoarthritis (OA) is the most frequent form of arthritis, with major implications for individual and public health care without effective treatment available. The field of joint imaging, and particularly magnetic resonance (MR) imaging, has evolved rapidly owing to technical advances and the application of these to the field of clinical research. Cartilage imaging certainly is at the forefront of these developments. In this review, the different aspects of OA imaging and cartilage assessment, with an emphasis on recent advances, will be presented. The current role of radiography, including advances in the technology for joint space width assessment, will be discussed. The development of various MR imaging techniques capable of facilitating assessment of cartilage morphology and the methods for evaluating the biochemical composition of cartilage will be presented. Advances in quantitative morphologic cartilage assessment and semiquantitative whole-organ assessment will be reviewed. Although MR imaging is the most important modality in imaging of OA and cartilage, others such as ultrasonography play a complementary role that will be discussed briefly.

7-T MR-from research to clinical applications?

Over 20 000 MR systems are currently installed worldwide and, although the majority operate at magnetic fields of 1.5 T and below (i.e. about 70%), experience with 3‐T (in high‐field clinical diagnostic imaging and research) and 7‐T (research only) human MR scanners points to a future in functional and metabolic MR diagnostics. Complementary to previous studies, this review attempts to provide an overview of ultrahigh‐field MR research with special emphasis on emerging clinical applications at 7 T. We provide a short summary of the technical development and the current status of installed MR systems. The advantages and challenges of ultrahigh‐field MRI and MRS are discussed with special emphasis on radiofrequency inhomogeneity, relaxation times, signal‐to‐noise improvements, susceptibility effects, chemical shifts, specific absorption rate and other safety issues. In terms of applications, we focus on the topics most likely to gain significantly from 7‐T MR, i.e. brain imaging and spectroscopy and musculoskeletal imaging, but also body imaging, which is particularly challenging. Examples are given to demonstrate the advantages of susceptibility‐weighted imaging, time‐of‐flight MR angiography, high‐resolution functional MRI, 1H and 31P MRSI in the human brain, sodium and functional imaging of cartilage and the first results (and artefacts) using an eight‐channel body array, suggesting future areas of research that should be intensified in order to fully explore the potential of 7‐T MR systems for use in clinical diagnosis. Copyright