The median effective dose and number of examinations per quarter year in mSv for thorax-abdomen-pelvis CT examinations.

<p>With the introduction the IR system (between 1/11 and 2/11) a significant reduction in radiation exposure can be reported. The clinical value of a DMS is demonstrated with the increase in effective dose in 4/11 and the direct detection and correction. </p

The median effective dose and number of examinations per quarter year in mSv for all examination between January 2010 and December 2012.

<p>With the introduction the IR system (between 1/11 and 2/11) a significant reduction in radiation exposure can be reported.</p

The median effective dose and number of examinations per quarter year in mSv for low dose scans of the cranial (for example sinuses).

<p>Note it is important to point out that for unenhanced neurological CT scan the effect of IR in combination with a wide-detector configuration is naturally minor.</p

Ultra Low Dose CT Pulmonary Angiography with Iterative Reconstruction

<div><p>Objective</p><p>Evaluation of a new iterative reconstruction algorithm (IMR) for detection/rule-out of pulmonary embolism (PE) in ultra-low dose computed tomography pulmonary angiography (CTPA).</p><p>Methods</p><p>Lower dose CT data sets were simulated based on CTPA examinations of 16 patients with pulmonary embolism (PE) with dose levels (DL) of 50%, 25%, 12.5%, 6.3% or 3.1% of the original tube current setting. Original CT data sets and simulated low-dose data sets were reconstructed with three reconstruction algorithms: the standard reconstruction algorithm “filtered back projection” (FBP), the first generation iterative reconstruction algorithm iDose and the next generation iterative reconstruction algorithm “Iterative Model Reconstruction” (IMR). In total, 288 CTPA data sets (16 patients, 6 tube current levels, 3 different algorithms) were evaluated by two blinded radiologists regarding image quality, diagnostic confidence, detectability of PE and contrast-to-noise ratio (CNR).</p><p>Results</p><p>iDose and IMR showed better detectability of PE than FBP. With IMR, sensitivity for detection of PE was 100% down to a dose level of 12.5%. iDose and IMR showed superiority to FBP regarding all characteristics of subjective (diagnostic confidence in detection of PE, image quality, image noise, artefacts) and objective image quality. The minimum DL providing acceptable diagnostic performance was 12.5% (= 0.45 mSv) for IMR, 25% (= 0.89 mSv) for iDose and 100% (= 3.57 mSv) for FBP. CNR was significantly (p < 0.001) improved by IMR compared to FBP and iDose at all dose levels.</p><p>Conclusion</p><p>By using IMR for detection of PE, dose reduction for CTPA of up to 75% is possible while maintaining full diagnostic confidence. This would result in a mean effective dose of approximately 0.9 mSv for CTPA.</p></div

Contrast-to-noise ratio.

<p>Contrast-to-noise ratio of a central pulmonary artery as a central vessal (cCNR) for all reconstruction algorithms and dose levels shown as mean ± standard deviation. * = significance compared to FBP and iDose at the corresponding dose level (p < 0.001). # = significance compared to FBP at the corresponding dose level (p < 0.001). Significance levels were calculated using Student's t-test. <i>FBP = filtered back projection</i>, <i>iDose = iterative dose reduction</i>, <i>IMR = iterative model reconstruction</i>.</p

Comparison of FBP, iDose and IMR—coronal view at full dose.

<p>Coronal tomographic slices of a 72-year-old male patient. The images were reconstructed with FBP, iDose and IMR (from left to right) at full dose (100% dose-level, meaning 85 mA, 100 kV and 2.25 mSv for this patient). Central and segmental pulmonary emboli can be clearly identified (arrows). The red dashed rectangle indicates the enlarged view in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0162716#pone.0162716.g004" target="_blank">Fig 4</a>. <i>FBP = filtered back projection</i>, <i>iDose = iterative dose reduction</i>, <i>IMR = iterative model reconstruction</i></p

Comparison of FBP, iDose and IMR at dose levels of 3.1–100%.

<p>Enlarged view of the coronal tomographic slices of the chest from <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0162716#pone.0162716.g003" target="_blank">Fig 3</a>, indicated by the red dashed rectangle. Comparison of FBP (top), iDose (middle) and IMR (bottom) at different dose levels (from left to right: 100%–50%–25%–12.5%–6.3%–3.1%). Emboli are located in the right pulmonary artery, the left upper and lower lobar artery and in several segmental arteries of the left lung. Note the good detectability even at ultra-low dose levels with IMR. With iDose emboli are also detectable but image quality is inferior to IMR. With FBP, emboli are not certainly detectable at lower dose levels. <i>FBP = filtered back projection</i>, <i>iDose = iterative dose reduction</i>, <i>IMR = iterative model reconstruction</i>.</p

Overall diagnostic confidence.

<p>Medians of overall diagnostic confidence in detection of PE shown as box-and-whisker plots at different dose levels (3.1–100% of the original dose level). IMR performs significantly better, providing high diagnostic confidence also at 25%, 12.5% and 6.3% of the original radiation dose. <b>*</b> = significance compared to iDose at the corresponding dose level (* = p<0.05, ** = p<0.01). # = significance compared to FBP at the corresponding dose level (p<0.01). Values are shown as the mean of the medians of both raters. <i>FBP = filtered back projection</i>, <i>iDose = iterative dose reduction</i>, <i>IMR = iterative model reconstruction</i>.</p