Assessment of attenuation properties for SLA and SLS 3D-printing materials in X-ray imaging and nuclear medicine.

In recent years, access to 3D printers has become increasingly affordable. Alongside industrial and private applications, the significance of 3D printing in the clinical context is also growing. For instance, 3D printing processes enable the production of individual anatomical models that can be used to support patient communication or aid in surgical planning. While filament 3D printing is common, stereolithography (SLA) and selective laser sintering (SLS) printing processes offer higher precision. For the use of 3D printing materials in radiology, understanding their attenuation properties concerning ionizing radiation is crucial. Polymethyl methacrylate (PMMA) serves as an important reference material for radiological applications in this regard. In this research, linear- and mass attenuation coefficients of 38 SLA-/SLS-materials from Formlabs (Somerville, Massachusetts, USA) and PMMA will be determined through intensity measurements in nuclear medicine for the radionuclides technetium-99 m and iodine-131, as well as for X-ray imaging in the range of 60 kVp - 110 kVp tube voltage. Based on the mass attenuation coefficients, correction factors in respect to PMMA will be calculated for each material. A significant number of materials exhibit a deviance within approximately ±5% in respect to PMMA regardless of radiation energy. However, certain materials from the dental and industrial application show deviances up to +500% at the lower end of radiation energy spectrum. In conclusion, most materials can be considered equivalent to PMMA with only minor adjustments required. Materials with high deviances can be utilized as high-contrast materials in custom X-ray phantoms.

Radiation Exposure in Interventional Stroke Treatment : Analysis of the German Neurointerventional Database (DeGIR/DGNR) from 2019 to 2021.

PURPOSE: To evaluate patient-related radiation exposure in interventional stroke treatment by analyzing data from the German Society for Interventional Radiology and Minimally Invasive Therapy (DeGIR) and the German Society of Neuroradiology (DGNR) quality registry from 2019-2021. METHODS: The DeGIR/DGNR registry is the largest database of radiological interventions in Germany. Since the introduction of the registry in 2012, the participating hospitals have entered clinical and dose-related data on the procedures performed. To evaluate the current diagnostic reference level (DRL) for mechanical thrombectomy (MT) in stroke patients, we analyzed interventional data from 2019 to 2021 with respect to the reported dose area product (DAP) and factors that might contribute to the radiation dose, such as the localization of the occlusion, technical success using the modified treatment in cerebral ischemia (mTICI) score, number of passages, technical approach, additional intracranial/extracranial stenting, and case volume per center. RESULTS: A total of 41,538 performed MTs from 180 participating hospitals were analyzed. The median DAP for MT was 7337.5 cGy∙cm2 and the corresponding interquartile range (IQR) Q25 = 4064 cGy∙cm2 to Q75 = 12,263 cGy∙cm2. In addition, we discovered that the dose was significantly influenced by occlusion location, number of passages, case volume per center, recanalization score, and additional stenting. CONCLUSION: We conducted a retrospective study on radiation exposure during MT in Germany. Based on the results of more than 41,000 procedures, we observed that the DRL of 14,000 cGy·cm2 is currently appropriate but may be lowered over the next years. Furthermore, we identified several factors that contribute to high radiation exposure. This can aid in detecting the cause of an exceeded DRL and optimize the treatment workflow.

Clinical evaluation of a novel head protection system for interventional radiologists.

PURPOSE: A novel two-part protective system consisting of a modified thyroid collar and a head protection is intended to reduce the radiation dose to the examiners head during fluoroscopy-guided interventions. In this pilot study, we tested this protection system under real-life conditions in general radiological and neuroradiological interventions. METHODS: Two sets of the protection system (set A and B) were equipped with 12 thermoluminiscence detectors (TLD). For simultaneous measurement of radiation exposure and dose-reduction, each six TLDs were fixed to the inner side and on the corresponding outer side of the protection system. Set A was used exclusively for general radiological interventions and set B exclusively for neuroradiological interventions. To compare the staff exposure in general radiology and neuroradiology, dose values were normalized to a DAP of 10 000 µGy∙m2. RESULTS: The sets were tested during 20 general radiological interventions and 32 neuroradiological interventions. In neuroradiology, the mean normalized radiation exposure was 13.44 ± 1.36 µSv/10000 µGy∙m2 at the head protection and 22.27 ± 2.09 µSv/10 000 µGy∙m2 at the thyroid collar. In general radiology, the corresponding results were 29.91 ± 4.19 µSv/10 000 µGy∙m2 (head protection) and 68.07 ± 17.25 µSv/10 000 µGy∙m2 (thyroid collar). Thus, mean dose exposure was 2.5 times higher in general radiological interventions (p = 0.016). The use of the protection system resulted in a mean dose reduction of 81.2 ± 11.1 % (general radiology) and 92.1 ± 4.2 % (neuroradiology; p = 0.016). CONCLUSION: Fluoroscopy-guided interventions lead to significant radiation exposure of the head area for the examiner. The novel protection system tested led to a significant dose reduction of 80-90%, depending on the type of intervention.

Individual calculation of perfusion activity based on ventilation efficiency for V/P-SPECT.

AIM: Implementation of the individual calculation of perfusion activity to ensure the guideline-compliant ratio of perfusion to ventilation (P/V-ratio) of ≥ 3 in the diagnosis of acute pulmonary embolism (PE) using V/P-SPECT. MATERIAL AND METHODS: 50 consecutive V/P-SPECT examinations, in which a standard activity of 160 MBq was applied for perfusion imaging, are evaluated retrospectively. Based on this patient group an activity factor is determined, which provides a correlation between the applied perfusion activity and the expected perfusion counts of the gamma camera. Using the mean activity factor, the perfusion activity required for a P/V-ratio of four is calculated using the previously acquired ventilation count rate. This is applied prospectively to the 100 subsequent examinations. RESULTS: The mean perfusion activity factor is (54.56 ± 10.13) cps/MBq. The individually calculated perfusion activities range from 80 MBq to 200 MBq with an average value of (146.9 ±â€Š35.3) MBq and a median of 140 MBq. The individual activity calculation thus reduced the mean perfusion activity by 8.2 % and the median by 12.5 %. In addition, the individual calculation reduced the proportion of P/V ratios < 3 from 14 % to 0 % and the proportion of P/V ratios > 5 from 24 % to 19 %. CONCLUSION: The presented method for the individual calculation of perfusion activity offers a simple way to ensure a guideline-compliant P/V-ratio. Furthermore, unnecessarily high perfusion activity as a result of inadequate ventilation can be avoided.

Investigation of Radiation Exposure of Patients with Acute Ischemic Stroke during Mechanical Thrombectomy. / Untersuchung der Strahlenexposition des Patienten mit akutem ischämischem Schlaganfall während der mechanischen Thrombektomie.

PURPOSE: In radiological interventions, the skin is the most exposed organ. The aim of this study was to investigate the local dose exposure and the resulting risk of deterministic radiation effects for patients who underwent mechanichal thrombectomy. MATERIALS AND METHODS: The examination protocols of 50 consecutive stroke patients who underwent mechanical thrombectomy from September 2016 to April 2017 were evaluated in this study. All procedures were performed on a biplanar angiographic suite. The local skin equivalent dose H P(0.07) was calculated retrospectively using the recorded radiation data and previously measured conversion factors. The in-vitro determination of the conversion factors was performed with a silicon semiconductor detector on the surface of an Alderson-Rando head phantom depending on the radiation quality. RESULTS: Vessel occlusion was located in the M1 and M2 segments of the cerebral artery media (n = 32), the internal carotid artery or carotid-T (n = 12) and the basilar artery (n = 6). The fluoroscopy times ranged from 5.7 minutes to 137.3 minutes with an average value of 39.5 ±â€Š4.1 minutes. The determined skin equivalent dose values ranged from 0.16 ±â€Š0.02 Gy to 4.80 ±â€Š0.51 Gy, with the mean value being 1.00 ±â€Š0.14 Gy. In 3 out of 50 cases (6 %), the threshold value for skin reactions of 3 Gy published by the German Radiation Protection Commission was exceeded. A further 15 patients (36 %) were exposed to a dose of 1-3 Gy. The highest dose values were achieved during long procedures with occlusions in the posterior circulation and carotid occlusions. In addition, a local dose reference level of 1.24 ±â€Š0.15 Gy could be determined for the skin equivalent dose in mechanical thrombectomies for our center. CONCLUSION: Even during a modern neuroradiological intervention, such as mechanical thrombectomy, radiation doses to the patient are produced and can lead to deterministic radiation damage to the skin in approximately 6 % of cases. Systematic monitoring of local dose quantities, such as H P(0.07), seems appropriate. Possibilities for recording and reducing the local dose load should be developed by the interventional teams in cooperation with a medical physics expert. KEY POINTS: · In 64 % of the thrombectomies the skin equivalent doses were in the harmless range (< 1 Gy).. · In 6 % of the patients higher H P(0.07) values were determined, which can lead to deterministic radiation damage to the skin.. · To avoid deterministic damage during neurointerventions, H P(0.07) should be recorded (combined measuring chambers).. · For longer interventions, precautions should be taken to reduce the radiation dose.. CITATION FORMAT: · Bärenfänger F, Block A, Rohde S. Investigation of Radiation Exposure of Patients with Acute Ischemic Stroke during Mechanical Thrombectomy. Fortschr Röntgenstr 2019; 191: 1099 - 1106.