Purpose An unmet need in carbon‐13 (13C)‐MRI is a transmit system that provides uniform excitation across a large FOV and can accommodate patients of wide‐ranging body habitus. Due to the small difference between the resonant frequencies, sodium‐23 (23Na) coil developments can inform 13C coil design while being simpler to assess due to the higher naturally abundant 23Na signal. Here we present a removable 23Na birdcage, which also allows operation as a 13C abdominal coil. Methods We demonstrate a quadrature‐driven 4‐rung 23Na birdcage coil of 50 cm in length for both 23Na and 13C abdominal imaging. The coil transmit efficiencies and B1+ maps were compared to a linearly driven 13C Helmholtz‐based (clamshell) coil. SNR was investigated with 23Na and 13C data using an 8‐channel 13C receive array within the 23Na birdcage. Results The 23Na birdcage longitudinal FOV was > 40 cm, whereas the 13C clamshell was < 32 cm. The transmit efficiency of the birdcage at the 23Na frequency was 0.65 µT/sqrt(W), similar to the clamshell for 13C. However, the coefficient of variation of 23Na‐B1+ was 16%, nearly half that with the 13C clamshell. The 8‐channel 13C receive array combined with the 23Na birdcage coil generated a greater than twofold increase in 23Na‐SNR from the central abdomen compared with the birdcage alone. Discussion This 23Na birdcage coil has a larger FOV and improved B1+ uniformity when compared to the widely used clamshell coil design while also providing similar transmit efficiency. The coil has the potential to be used for both 23Na and 13C imaging.

Aims Plaque structural stress (PSS) is a major cause of atherosclerotic plaque rupture and major adverse cardiovascular events (MACE). We examined the predictors of changes in peak and mean PSS (ΔPSSpeak, ΔPSSmean) in three studies of patients receiving either standard medical or high-intensity statin (HIS) treatment. Methods and results We examined changes in PSS, plaque size and composition between 7,348 co-registered baseline and follow-up virtual-histology intravascular ultrasound images in patients receiving standard medical treatment (controls, n = 18) or HIS (atorvastatin 80mg, n = 20, or rosuvastatin 40mg, n = 22). The relationship between changes in PSSpeak and plaque burden (PB) differed significantly between HIS and control groups (p &lt; 0.001). Notably, PSSpeak increased significantly in control lesions with PB &gt; 60% (p = 0.04), but not with HIS treatment. However, ΔPSSpeak correlated poorly with changes in lumen and plaque area or PB, plaque composition or lipid lowering. In contrast, ΔPSSpeak correlated significantly with changes in lumen curvature, irregularity and roughness (p &lt; 0.05), all of which were reduced in HIS patients. ΔPSSmean correlated with changes in lumen area, PA, PB, and circumferential calcification, and was unchanged with either treatment. Conclusion Our observational study shows that PSSpeak changes over time were associated with baseline disease severity and treatment. The PSSpeak increase seen in advanced lesions with standard treatment was associated with remodelling artery geometry and plaque architecture, but this was not seen after HIS treatment. Smoothing plaques by reducing plaque/lumen roughness, irregularity and curvature represent a novel mechanism whereby high-intensity statins may reduce PSS, and thus may protect against plaque rupture and MACE.

Objective: Mechanical properties of healthy, aneurysmal, and atherosclerotic arterial tissues are essential for assessing the risk of lesion development and rupture. Strain energy density function (SEDF) has been widely used to describe these properties, where material constants of the SEDF are traditionally determined using the ordinary least square (OLS) method. However, the material constants derived using OLS are usually dependent on initial guesses. Methods: To avoid such dependencies, Bayesian inference-based estimation was used to fit experimental stress-stretch curves of 312 tissue strips from 8 normal aortas, 19 aortic aneurysms, and 21 carotid atherosclerotic plaques to determine the constants, C 1 , D 1 , and D 2 of the modified Mooney-Rivlin SEDF. Results: Compared with OLS, material constants varied much less with prior in the Bayesian inferencebased estimation. Moreover, fitted material constants differed amongst distinct tissue types. Atherosclerotic tissues associated with the biggest D 2 , an indicator of the rate of increase in stress during stretching, followed by aneurysmal tissues and those from normal aortas. Histological analyses showed that C 1 and D 2 were associated with elastin content and details of the colla