Dose Reduction on Computed Tomography Angiography Using Adaptive Control Techniques

With the advent of multi-slice computed tomography (CT) scanner and the sophisticated CT reconstruction algorithm, CT Angiography (CTA) is increasingly used to evaluate patient with vascular diseases (Fleischmann et al., 2006; Chow & Rubin, 2002; Rubin at al., 2001). It has many advantages over the conventional catheter angiograms: 1) non-invasiveness, 2) short acquisition time, 3) multiple viewing methods, and 4) low cost. However, the radiation exposure of CT scan has become of a wide concern due to its induction to genetic, cancerous and other diseases (Brenner et al., 2001; de Gonzalez & Darby et al., 2004). According to (Mettler et al., 2000), CT scan delivers 2/3 of the total radiation dose every year in US, and this number is climbing. On June 19th, 2007, the New York Times reported that "the percapita dose of ionizing radiation from clinical imaging exams in the U.S. increased almost 600% from 1980 to 2006". Brenner (Brenner et al., 2001) reported that diagnostic X-rays, indicating that radiation from medical and dental scans, cause about 700 cases of cancer per year in Britain and more than 5,600 cases in US. To that end, every effort to reduce the radiation dose is appreciated and the well-known ALARA (As Low As Reasonably Achievable) principle is widely accepted in the medical community. There are many studies have been reported on dose reduction for CT scan. Wintersperger and his colleagues (Wintersperger et al., 2000) used lower kilo-voltage and claimed the resultant image had similar sensitivity and accuracy. In Fraioli’s studies (Fraioli et al., 2006), lower tube currents were used and the resultant image quality was claimed to be good enough for diagnosis. Generally, dose reduction is contrary to the image quality. In other words, reducing the radiation dose will sacrifice the image quality. However, with the advanced CT reconstruction algorithm (Yan et al., 2008; Zeng et al., 2007; Liu et al., 2009; Yin et al., 2009) and post-processing techniques (Salmon et al., 2009; Benitez et al., 2009; Zeng et al., 2008; Zhang et al., 2008), the resultant images could be held to certain diagnosis level while the radiation dose is reduced lot. Recently, control technique is found very useful in CT. It can be applied to improve the CT image quality (Lu et al., 2008; H. Bai et al., 2008), and to reduce the radiation dose reduction, for example, Automatic Exposure Control (AEC) program, which modulates the tube current to maintain the same x-ray attenuation level according to the scan angle/position of the human body.