Context sensitive cardiac x-ray imaging: a machine vision approach to x-ray dose control

Modern cardiac x-ray imaging systems regulate their radiation output based on the thickness of the patient to maintain an acceptable signal at the input of the x-ray detector. This approach does not account for the context of the examination or the content of the image displayed. We have developed a machine vision algorithm that detects iodine-filled blood vessels and fits an idealized vessel model with the key parameters of contrast, diameter, and linear attenuation coefficient. The spatio-temporal distribution of the linear attenuation coefficient samples, when appropriately arranged, can be described by a simple linear relationship, despite the complexity of scene information. The algorithm was tested on static anthropomorphic chest phantom images under different radiographic factors and 60 dynamic clinical image sequences. It was found to be robust and sensitive to changes in vessel contrast resulting from variations in system parameters. The machine vision algorithm has the potential of extracting real-time context sensitive information that may be used for augmenting existing dose control strategies

Impact of latest generation cardiac interventional X-ray equipment on patient image quality and radiation dose for trans-catheter aortic valve implantations

OBJECTIVES: This study aimed to determine whether a reduction in radiation dose was found whilst maintaining a clinically acceptable level of image quality for trans-catheter aortic valve implantation (TAVI) patients using a new cardiac interventional X-ray system with state-of-the-art image enhancement and X-ray optimisation, compared to the cardiac X-ray system which was previously used for TAVI (the reference system). METHODS: Patient dose and image data were retrospectively collected from an AlluraClarity (Philips Healthcare) and Axion Artis (Siemens Healthcare), the new and reference X-ray systems respectively. Patient procedure dose area product (DAP) and fluoroscopy duration of 41 patient cases from each X-ray system were compared using a Wilcoxon test on median values. Significant reductions in patient dose (p<<0.001) were found for the new system with no significant change in fluoroscopy duration (p=0.052); procedure DAP reduced by 55%, fluoroscopy DAP by 48% and “cine” acquisition DAP by 61%. Ten patient aortograms from each X-ray system (20 total) were scored by 32 observers on a continuous scale to assess the clinical image quality at the given phase of the TAVI procedure. Scores were dichotomised by acceptability and analysed using a Chi-squared test; there was no significant difference between the two X-ray systems (p=0.06). CONCLUSIONS: The new cardiac X-ray system demonstrated a very significant reduction in patient dose with no loss of clinical image quality. ADVANCES IN KNOWLEDGE: The huge growth of TAVI may impact on the radiation exposure incurred by cardiac patients and particularly on operators including not only interventional cardiologists, also anaesthetists for TAVI procedures; the cumulative exposure to interventional cardiologists performing high volume TAVI over a 30 - 40 year career may be harmful. The Phillips Clarity upgrade including improved digital image enhancement and optimised X-ray settings significantly reduced the amount of radiation used without reducing clinically acceptable image quality