Handling of Incidents in the Clinical Application of Ionizing Radiation in Diagnostic and Interventional Radiology - a Multi-center Study. / Umgang mit unbeabsichtigten Expositionen bei medizinischen Anwendungen ionisierender Strahlung in der Röntgendiagnostik und interventionellen Radiologie ­ eine Multi-Center-Studie.

PURPOSE: According to the German legislation and regulation of radiation protection, i. e. Strahlenschutzgesetz und Strahlenschutzverordnung (StrlSchG and StrlSchV), which came into force on 31st December 2018, significant unintended or accidential exposures have to be reported to the competent authority. Furthermore, facilities have to implement measures to prevent and to recognize unintended or accidental exposures as well as to reduce their consequences. We developed a process to register incidents and tested its application in the framework of a multi-center-study. MATERIALS AND METHODS: Over a period of 12 months, 16 institutions for x-ray diagnostics and interventions, documented their incidents. Documentation of the incidents was conducted using the software CIRSrad, which was developed, released for testing purposes and implemented in the frame of the study. Reporting criteria of the project were selected to be more sensitive compared to the legal criteria specifying "significant incidents". Reported incidents were evaluated after four, eight, and twelve months. Finally, all participating institutions were interviewed on their experience with the software and the correlated effort. RESULTS: The rate of reported incidents varied between institutions as well as between modalities. The majority of incidents were reported in conventional x-ray imaging, followed by computed tomography and therapeutic interventions. Incidents were attributed to several different causes, amongst others to the technical setup and patient positioning (19 %) and patient movement or insufficient cooperativeness of the patient (18 %). Most incidents were below corresponding thresholds stated in StrlSchV. The workload for documenting the incidents was rated as appropriate. CONCLUSION: It is possible to monitor and handle incidents complient with legal requirements with an acceptable effort. The number of reported incidents can be increased by frequent trainings on the detection and the processing workflow, on the software and legal regulation as well as by a transparent error handling within the institution. KEY POINTS: · The software CIRSrad was developed to enable the present study and as prototype platform for a future radiological incident management system.. · 586 exceedances of thresholds were recorded by 16 facilities in a period of one year.. · Frequent trainings of all users increase the number of reported cases.. CITATION FORMAT: · Müller BS, Singer J, Stamm G et al. Handling of Incidents in the Clinical Application of Ionizing Radiation in Diagnostic and Interventional Radiology - a Multi-center Study. Fortschr Röntgenstr 2022; 194: 400 - 408.

Relaxation-compensated CEST-MRI at 7 T for mapping of creatine content and pH--preliminary application in human muscle tissue in vivo.

The small biomolecule creatine is involved in energy metabolism. Mapping of the total creatine (mostly PCr and Cr) in vivo has been done with chemical shift imaging. Chemical exchange saturation transfer (CEST) allows an alternative detection of creatine via water MRI. Living tissue exhibits CEST effects from different small metabolites, including creatine, with four exchanging protons of its guanidinium group resonating about 2 ppm from the water peak and hence contributing to the amine proton CEST peak. The intermediate exchange rate (≈ 1000 Hz) of the guanidinium protons requires high RF saturation amplitude B1. However, strong B1 fields also label semi-solid magnetization transfer (MT) effects originating from immobile protons with broad linewidths (~kHz) in the tissue. Recently, it was shown that endogenous CEST contrasts are strongly affected by the MT background as well as by T1 relaxation of the water protons. We show that this influence can be corrected in the acquired CEST data by an inverse metric that yields the apparent exchange-dependent relaxation (AREX). AREX has some useful linearity features that enable preparation of both concentration, and--by using the AREX-ratio of two RF irradiation amplitudes B1--purely exchange-rate-weighted CEST contrasts. These two methods could be verified in phantom experiments with different concentration and pH values, but also varying water relaxation properties. Finally, results from a preliminary application to in vivo CEST imaging data of the human calf muscle before and after exercise are presented. The creatine concentration increases during exercise as expected and as confirmed by (31)P NMR spectroscopic imaging. However, the estimated concentrations obtained by our method were higher than the literature values: cCr,rest=24.5±3.74mM to cCr,ex=38.32±13.05mM. The CEST-based pH method shows a pH decrease during exercise, whereas a slight increase was observed by (31)P NMR spectroscopy.

Quantitative pulsed CEST-MRI using Ω-plots.

Chemical exchange saturation transfer (CEST) allows the indirect detection of dilute metabolites in living tissue via MRI of the tissue water signal. Selective radio frequency (RF) with amplitude B1 is used to saturate the magnetization of protons of exchanging groups, which transfer the saturation to the abundant water pool. In a clinical setup, the saturation scheme is limited to a series of short pulses to follow regulation of the specific absorption rate (SAR). Pulsed saturation is difficult to describe theoretically, thus rendering quantitative CEST a challenging task. In this study, we propose a new analytical treatment of pulsed CEST by extending a former interleaved saturation-relaxation approach. Analytical integration of the continuous wave (cw) eigenvalue as a function of the RF pulse shape leads to a formula for pulsed CEST that has the same structure as that for cw CEST, but incorporates two form factors that are determined by the pulse shape. This enables analytical Z-spectrum calculations and permits deeper insight into pulsed CEST. Furthermore, it extends Dixon's Ω-plot method to the case of pulsed saturation, yielding separately, and independently, the exchange rate and the relative proton concentration. Consequently, knowledge of the form factors allows a direct comparison of the effect of the strength and B1 dispersion of pulsed CEST experiments with the ideal case of cw saturation. The extended pulsed CEST quantification approach was verified using creatine phantoms measured on a 7 T whole-body MR tomograph, and its range of validity was assessed by simulations.