Novel reconstruction method for three-dimensional axial continuously moving table whole-body magnetic resonance imaging featuring autocalibrated parallel imaging GRAPPA

[Prognostic value of cardiovascular MRI in diabetics]

CLINICAL/METHODICAL ISSUE

Despite an increased cardiovascular risk in patients with diabetes mellitus they are a heterogeneous population with very different individual manifestation of diseases; therefore, a profound stratification is recommended.

STANDARD METHODS

Clinical examinations and blood biomarkers are typically used in diabetic patients to determine the risk for developing cardio-cerebrovascular events.

METHODICAL INNOVATIONS

Cardiac as well as whole-body magnetic resonance imaging (MRI) including cardiovascular sequences are established methods for clinical diagnostics. Their significance in predicting the outcome and the corresponding risk stratification for patients with diabetes is becoming increasingly more important based on recent study results.

PERFORMANCE

Late gadolinium enhancement (LGE) in cardiac MRI detects silent myocardial ischemia in up to 30% of diabetic patients, which is associated with a hazard ratio of 3-6 for cardiovascular events. Regional left ventricular wall motion abnormalities and decreased ejection fraction also have a prognostic value in diabetics. Based on whole-body MRI, the vessel score as well as carotid artery stenosis have been evaluated as additional predictors for cardio-cerebrovascular events.

ACHIEVEMENTS

The MRI-based predictors have independent and incremental prognostic value beyond traditional risk stratification for cardio-cerebrovascular events; however, only the comprehensive assessment of whole-body MRI including angiography allows the identification of patients who remain free of cardio-cerebrovascular events over a period of 6 years.

PRACTICAL RECOMMENDATIONS

Cardiac MRI, particularly the detection of LGE, can be recommended for risk stratification of patients with diabetes mellitus. The clinical relevance of the added prognostic value of whole-body MRI needs to be clarified in further studies.

Whole-body MRI in adult inflammatory myopathies: Do we need imaging of the trunk?

OBJECTIVE

To evaluate whether imaging of the trunk could be omitted in patients with inflammatory myopathies without losing diagnostic accuracy using a restricted whole-body magnetic resonance imaging (rWB-MRI) protocol.

METHODS

After approval by the institutional review board, this study was performed in 63 patients (male/female, 13/50; median age, 52 years; range, 20-81 years) with new-onset myopathic symptoms (group 1, n = 41) or previously diagnosed inflammatory myopathy (group 2, n = 22). After performing whole-body MRI (WB-MRI) at 3.0 Tesla, myositis and fatty atrophy were evaluated in different muscles by two independent radiologists. The intra-class correlation coefficient (ICC) was calculated to evaluate inter-observer reliability.

RESULTS

Acquisition time was 56:01 minutes for WB-MRI and 37:37 minutes (32.8 % shorter) for rWB-MRI. In group 1, 14 patients were diagnosed with inflammatory myopathy based on muscle biopsy. rWB-MRI and WB-MRI showed equal sensitivity (42.9 %) and specificity (100 %) for myositis, and showed equal sensitivity (71.4 %) and similar specificity (63.0 % and 48.1 %, respectively) for fatty atrophy. No myositis was found in the body trunk in any patient. Inter-observer reliability was between substantial and perfect (ICC, 0.77-1.00).

CONCLUSIONS

rWB-MRI showed diagnostic accuracy similar to WB-MRI for inflammatory myopathy at markedly reduced overall acquisition time.

KEY POINTS

• Whole-body MRI (WB-MRI) is a time-consuming imaging modality. • A shortened MRI protocol was evaluated for inflammatory myopathies. • The proposed protocol showed diagnostic accuracy similar to WB-MRI.

Field of view extension and truncation correction for MR-based human attenuation correction in simultaneous MR/PET imaging

PURPOSE

In quantitative PET imaging, it is critical to accurately measure and compensate for the attenuation of the photons absorbed in the tissue. While in PET/CT the linear attenuation coefficients can be easily determined from a low-dose CT-based transmission scan, in whole-body MR/PET the computation of the linear attenuation coefficients is based on the MR data. However, a constraint of the MR-based attenuation correction (AC) is the MR-inherent field-of-view (FoV) limitation due to static magnetic field (B0) inhomogeneities and gradient nonlinearities. Therefore, the MR-based human AC map may be truncated or geometrically distorted toward the edges of the FoV and, consequently, the PET reconstruction with MR-based AC may be biased. This is especially of impact laterally where the patient arms rest beside the body and are not fully considered.

METHODS

A method is proposed to extend the MR FoV by determining an optimal readout gradient field which locally compensates B0 inhomogeneities and gradient nonlinearities. This technique was used to reduce truncation in AC maps of 12 patients, and the impact on the PET quantification was analyzed and compared to truncated data without applying the FoV extension and additionally to an established approach of PET-based FoV extension.

RESULTS

The truncation artifacts in the MR-based AC maps were successfully reduced in all patients, and the mean body volume was thereby increased by 5.4%. In some cases large patient-dependent changes in SUV of up to 30% were observed in individual lesions when compared to the standard truncated attenuation map.

CONCLUSIONS

The proposed technique successfully extends the MR FoV in MR-based attenuation correction and shows an improvement of PET quantification in whole-body MR/PET hybrid imaging. In comparison to the PET-based completion of the truncated body contour, the proposed method is also applicable to specialized PET tracers with little uptake in the arms and might reduce the computation time by obviating the need for iterative calculations of the PET emission data beyond those required for reconstructing images.

Comparison of a new whole-body continuous-table-movement protocol versus a standard whole-body MR protocol for the assessment of multiple myeloma

OBJECTIVES

To evaluate a whole body (WB) continuous-table-movement (CTM) MR protocol for the assessment of multiple myeloma (MM) in comparison to a step-by-step WB protocol.

METHODS

Eighteen patients with MM were examined at 1.5T using a WB CTM protocol (axial T2-w fs BLADE, T1-w GRE sequence) and a step-by-step WB protocol including coronal/sagittal T1-w SE and STIR sequences as reference. Protocol time was assessed. Image quality, artefacts, liver/spleen assessability, and the ability to depict bone marrow lesions less than or greater than 1 cm as well as diffuse infiltration and soft tissue lesions were rated. Potential changes in the Durie and Salmon Plus stage and the detectability of complications were assessed.

RESULTS

Mean protocol time was 6:38 min (CTM) compared to 24:32 min (standard). Image quality was comparable. Artefacts were more prominent using the CTM protocol (P = 0.0039). Organ assessability was better using the CTM protocol (P < 0.001). Depiction of bone marrow and soft tissue lesions was identical without a staging shift. Vertebral fractures were not detected using the CTM protocol.

CONCLUSIONS

The new protocol allows a higher patient throughput and facilitates the depiction of extramedullary lesions. However, as long as vertebral fractures are not detectable, the protocol cannot be safely used for clinical routine without the acquisition of an additional sagittal sequence.

Whole body MR imaging in diabetes

Diabetes mellitus is a major cardiovascular risk factor and one of the major causes for morbidity and mortality worldwide. Diabetic complications have not only major impact on the quality of life of diabetic patients, but are also potentially life-threatening. Therefore prevention, diagnosis and therapy of these long-term complications are of high importance. However, diagnosis of the variety of complications from diabetes mellitus remains a diagnostic challenge and usually several diagnostic steps are necessary to diagnose or exclude these complications. In the last years whole body magnetic resonance imaging (WB-MRI) including whole body magnetic resonance angiography (WB-MRA) has been introduced for cardiovascular imaging and is now increasingly applied in clinical routine for the workup of patients with cardiovascular disease and for cardiovascular screening. The article summarizes rationales for WB-MRI in diabetes mellitus, technical concepts of disease specific cardiovascular WB-MRI in diabetes mellitus and discusses potential clinical consequences.