LAUSR

Three-dimensional gradient echo T1w MRI sequences of the brain after intravenous administration of gadoliniumbased contrast agents (3DT1-Gd) are routinely acquired during clinical workup. We report a signal loss of 3DT1-Gd of the skin and subcutaneous tissues, which occurs in most cases at the occipital pole and in fewer cases around the ears (see Fig. 1). Initially, we thought that this skin signal loss was due to an MR technique/head coil-related artifact. We, however, then observed the same artifact on different MR vendors with different head coils and occasionally even on CT. We therefore hypothesized that this skin signal loss artifact on post-contrast scans is related to local pressure notably on the occipital pole (due to the gravity of the head) as well as on the sides (due to headphones or conventional foam cushions used to stabilize the head). The problem is that those conventional foam cushions used in MRI are not visible on standard MR sequences. Thus, they were not seen to be the cause of local pressure and subsequent skin signal loss artifact on post-contrast scans up to date. We therefore compared conventional foam cushions as delivered with the scanner with optimized patient positioning cushions made out of air-filled thermoplastic polyurethane (TPU) foil chambers combined with expanded polystyrene (EPS) bead-filled chambers. The optimized patient positioning cushions allow for a high degree of variability and an individually adaptable immobilization to obtain a homogeneous distribution of skin pressure. We were able to demonstrate that skin signal loss disappeared with these optimized cushions (Fig. 2). This supports the hypothesis that skin signal loss is caused by local mechanical pressure. In conclusion, we postulate that the skin signal loss effect/artifact may in principle occur in all MR scanners, as well as in other parts of the bodies, yet depending on the spatial configuration of the MR table, coil, and foam, the severity and frequency of this skin signal loss should vary between different MR machines. Rarely, it is also observed on cranial CT. We postulate that the origin of this skin signal loss effect/artifact is local mechanical compression of the skin, leading to compression of the subcutaneous venous system and consequently to a reduced contrast agent uptake. We do not think that this compression effect is dangerous or harmful to the patient (at least if not applied for very long periods). Nevertheless, we demonstrate that optimized cushions may reduce this effect, which at the same time improve patient comfort. Consequently, we recommend optimized patient positioning and immobilization cushions. * Sven Haller [email protected]