Both film types are appropriate for dosimetry in MRT and the microscope is superior to the microdensitometer used before at the ESRF with respect to resolution and reproducibility. However, a very careful analysis of the image data is required. Dosimetry at low photon energies should be performed with great caution due to the energy sensitivity of the films. In this respect, HD-V2 films showed to have an advantage over HD-810 films. However, HD-810 films have a lower statistical noise level. When a higher resolution is required, e.g., for the dosimetry of pencil beam irradiations, noise may render HD-V2 films inapplicable.

No abstract

Purpose: To quantify the tissue sodium concentration (TSC) in cardiac 23 Na MRI.To evaluate the influence of different correction methods on the measured myocardial TSC. Methods: 23 Na MRI of four healthy subjects was conducted at a whole-body 7T MRI system using an oval-shaped 23 Na birdcage coil. Data acquisition was performed with a density-adapted 3D radial pulse sequence using a golden angle projection scheme. 1 H MRI data were acquired at a 3T MRI system to generate a myocardial mask. Retrospective cardiac and respiratory gating were used to reconstruct 23 Na MRI data in the diastolic phase and exhaled state. B 0 and B 1 inhomogeneity and partial volume (PV) effects were corrected. Relaxation times and TSC of ex vivo blood samples and calf muscle were determined. These values were used in the PV correction to estimate myocardial TSC, which was compared with the measured TSC of calf muscle. Results: Without any correction the measured myocardial TSC was (54 ± 5) mM.The applied correction methods reduced these values by (48 ± 5)% to (29 ± 3) mM, where PV correction had the largest effect (reduction of (34 ± 1)%). Respiratory and cardiac motion gating decreased the concentrations by (11 ± 1)%. With the applied setup, the corrections of B 0 and B 1 inhomogeneity (reduction of (3 ± 2)%) had negligible influences on TSC values. The resulting myocardial TSC was approximately 1.4-fold higher than the measured TSC of calf muscle tissue of the same healthy subjects ((20 ± 3) mM). |LOTT eT aL. |LOTT eT aL. F I G U R E 1Schematic outline of the measurements and the post-processing workflow. The process can be divided into a main path and a side path. The main part contains the cardiac 23 Na and 1 H MR measurements, all applied corrections and the determination of the myocardial TSC. In the side path, parameters, that are required for the corrections, such as relaxation times and sodium concentration of whole blood were determined for each volunteer individually F I G U R E 2 Retrospectively gated cardiac 23 Na in vivo data in a diastolic cardiac phase for one volunteer as an example. The not sorted 23 Na data (A) were reconstructed with the full set of projections. 49% of the projections were used to conduct the diastolic 23 Na image reconstruction (B). The measured sodium concentration in the diastolic image (C, red) is slightly reduced compared with the not sorted data (C, blue). Cardiac 23 Na data and line plots for the other three volunteers are shown in the Supporting Information Figure S3