Assessment of fitting methods and variability of IVIM parameters in muscles of the lumbar spine at rest

From Voxels to Physiology: A Review of Diffusion Magnetic Resonance Imaging Applications in Skeletal Muscle

Skeletal muscle has a classic structure function relationship; both skeletal muscle microstructure and architecture are directly related to force generating capacity. Biopsy, the gold standard for evaluating muscle microstructure, is highly invasive, destructive to muscle, and provides only a small amount of information about the entire volume of a muscle. Similarly, muscle fiber lengths and pennation angles, key features of muscle architecture predictive of muscle function, are traditionally studied via cadaveric dissection. Noninvasive techniques such as diffusion magnetic resonance imaging (dMRI) offer quantitative approaches to study skeletal muscle microstructure and architecture. Despite its prevalence in applications for musculoskeletal research, clinical adoption is hindered by a lack of understanding regarding its sensitivity to clinically important biomarkers such as muscle fiber cross-sectional area. This review aims to elucidate how dMRI has been utilized to study skeletal muscle, covering fundamentals of muscle physiology, dMRI acquisition techniques, dMRI modeling, and applications where dMRI has been leveraged to noninvasively study skeletal muscle changes in response to disease, aging, injury, and human performance. LEVEL OF EVIDENCE: 5 TECHNICAL EFFICACY: Stage 2.

Quantitative evaluation of placental microvascular blood flow and microstructure in fetal growth restriction with IVIM MRI

BACKGROUND

Intravoxel incoherent motion (IVIM) MRI uses diffusion-weighted (DW) MRI acquisitions to evaluate the microvascular and cellular environments of tissue. Due to these properties, IVIM has been increasingly utilized to evaluate abnormal placentation.

OBJECTIVE

Our primary objective was to compare IVIM parameters in the placenta of patients with fetal growth restriction and appropriate for gestational age controls across gestational ages. Our secondary aim was to quantify IVIM parameters in fetal versus maternal placental aspects to evaluate microvascular and parenchymal differences.

MATERIALS AND METHODS

With IRB approval, pregnant individuals with a diagnosis of fetal growth restriction (n=24) and controls (n=22) were retrospectively analyzed. DW-MRI data were collected at 1.5 T with nine b-values (range, 0 s/mm2 to 1,000 s/mm2). Data were processed by one non-blinded reader to obtain mean perfusion fraction (f), pseudo-diffusion coefficient (D*), their product fD*, and diffusion coefficient (D) in maternal and fetal aspects of the placenta, defined by bisecting the thickness of the placenta. Repeated measures of two-way ANOVAs were used to compare IVIM parameters in fetal and maternal placental aspects between participant groups. Correlations between IVIM parameters and gestational age were also evaluated in both groups.

RESULTS

The average gestational age at MRI was 27±4 weeks for both groups. The percentile estimated fetal weight was 5.4±5.9% for the fetal growth restriction group and 42.8±28.5% for controls (P<0.001). The parameters D* and fD*, related to microvascular blood flow and tissue perfusion, were significantly lower in participants with fetal growth restriction compared to controls (D*, 40.5 vs. 52.4×10-3 mm2/s, P=0.043; fD*, 14.7 vs. 21.0×10-3 mm2/s, P=0.019). No other differences were observed, nor associations between gestational age and IVIM parameters in either group.

CONCLUSION

Our results suggest reduced microvascular flow in placentas of patients with fetal growth restriction compared to controls.