Optimal scanning protocol of multislice CT virtual intravascular endoscopy in pre-aortic stent grafting: In vitro phantom study

Added Value of Computed Tomography Virtual Intravascular Endoscopy in the Evaluation of Coronary Arteries with Stents or Plaques

Coronary computed tomography angiography (CCTA) is a widely used imaging modality for diagnosing coronary artery disease (CAD) but is limited by a high false positive rate when evaluating coronary arteries with stents and heavy calcifications. Virtual intravascular endoscopy (VIE) images generated from CCTA can be used to qualitatively assess the vascular lumen and might be helpful for overcoming this challenge. In this study, one hundred subjects with coronary stents underwent both CCTA and invasive coronary angiography (ICA). A total of 902 vessel segments were analyzed using CCTA and VIE. The vessel segments were first analyzed on CCTA alone. Then, using VIE, the segments were classified qualitatively as either negative or positive for in-stent restenosis (ISR) or CAD. These results were compared, using ICA as the reference, to determine the added diagnostic value of VIE. Of the 902 analyzed vessel segments, CCTA/VIE had sensitivity, specificity, accuracy, positive predictive value, and negative predictive value (shown in %) of 93.9/90.2, 96.2/98.2, 96.0/97.7, 70.0/83.1, and 99.4/99.0, respectively, in diagnosing ISR or CAD, with significantly improved specificity (p = 0.025), accuracy (p = 0.046), and positive predictive value (p = 0.047). VIE can be a helpful addition to CCTA when evaluating coronary arteries.

The Additional Diagnostic Value of the Three-dimensional Volume Rendering Imaging in Routine Radiology Practice

Three-dimensional volume rendering (3DVR) is useful in a wide variety of medical-imaging applications. The increasingly advanced capabilities of CT and MRI to acquire volumetric data sets with isotropic voxels have resulted in the increased use of the 3DVR techniques for clinical applications. The two most commonly used techniques are the maximum intensity projection (MIP) and, more recently, 3DVR. Several kinds of medical imaging data could be reconstructed for 3D display, including CT, MRI, and ultrasonography (US). In particular, the 3D CT imaging has been developed, improved, and widely used of late. Understanding the mechanisms of 3DVR is essential for the accurate evaluation of the resulting images. Although further research is required to detect the efficiency of 3DVR in radiological applications, with wider availability and improved diagnostic performance, 3DVR is likely to enjoy widespread acceptance in the radiology practice going forward.

Dual-source CT angiography in aortic stent grafting: An in vitro aorta phantom study of image noise and radiation dose

RATIONALE AND OBJECTIVES

The aim of the study was to investigate the optimal protocols of dual-source computed tomography (CT) angiography in aortic stent grafting in terms of image noise and radiation dose, based on an in vitro phantom study.

MATERIALS AND METHODS

A series of helical CT cans were performed on a human aorta phantom using a dual-source CT scanner with kVp of 100, 120, and 140, corresponding mAs of 180, 150, and 100; slice thickness of 1.0, 1.5, and 2.0 mm; and pitch value of 0.5, 1.0, and 1.5, respectively. Image quality was determined by measuring the standard deviation (SD) on three-dimensional virtual intravascular endoscopy (VIE) images. Signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR) were measured on two-dimensional (2D) axial images at superior mesenteric artery (SMA), renal arteries, and aneurysm. Effective dose was determined based on dose-length product.

RESULTS

SD measured on VIE images was independent of kVp and pitch values but was determined by the slice thickness (P < .05) at the SMA and renal arteries. SNR and CNR measured on 2D images showed significant differences between variable kVp values and slice thicknesses (P < .05), but were independent of pitch values. The mean estimated effective dose for 120 kVp and 140 kVp protocols were 2.66 +/- 0.21 mSv and 2.68 +/- 0.18 mSv, respectively. The mean estimated effective dose for 100 kVp protocol was significantly lower (1.97 +/- 0.07 mSv, P < .0001). This indicates a reduction of 26.5% radiation dose when the kVp was lowered from 140 to 100.

CONCLUSION

A scanning protocol of 1.5-mm slice thickness, pitch 1.5 with 100 kVp, and 180 mAs is recommended for a dual-source CT angiography in aortic stent grafting as it leads to significant reduction of radiation dose while achieving diagnostic images.

Multislice CT angiography in the follow-up of fenestrated endovascular grafts: effect of slice thickness on 2D and 3D visualization of the fenestration stents

PURPOSE

To investigate the effect of multislice computed tomography (CT) protocols on the visualization of target vessel stents in patients with abdominal aortic aneurysm (AAA) treated with fenestrated endovascular grafts.

METHODS

Twenty-one patients (19 men; mean age 75 years, range 63-86) undergoing fenestrated endovascular repair of AAA were retrospectively studied. Multislice CT angiography was performed with several protocols, and the section thicknesses used in each were compared to identify any relationship between slice thickness and target vessel stents visualized on 2-dimensional (2D) axial, multiplanar reformatted (MPR), and 3-dimensional (3D) virtual intravascular endoscopy (VIE) images. Image quality was assessed based on the degree of artifacts and their effect on the ability to visualize the configuration, intra-aortic location, and intraluminal appearance of the target vessel stents and measure their protrusion into the aortic lumen.

RESULTS

There were 7 different multislice CT scanning protocols employed in the 21 patients (25 datasets, with 2 sets of follow-up images in 4 patients). The slice thicknesses and numbers (n) of studies included were 0.5 (n=3), 0.625 (n=6), 1.0 (n=1), 1.25 (n=9), 2.5 (n=3), 3.0 (n=1), and 5.0 mm (n=2). Of these CT protocols, images (especially 2D/3D reconstructions) acquired at 2.5, 3.0, and 5.0 mm were significantly compromised by interference from artifacts. Images acquired with a slice thickness of 1.0 or 1.25 mm were scored equal to or lower than those acquired with a submillimeter section thickness (0.5 or 0.625 mm), with minor degrees of artifacts resulting in acceptable image quality.

CONCLUSION

Visualization of the target vessel stents depends on the appropriate selection of multislice CT scanning protocols. Our results showed that studies performed with a slice thickness of 1.0 or 1.25 mm produced similar image quality to those with a thickness of 0.5 or 0.625 mm. Submillimeter slices are not recommended in imaging patients treated with fenestrated stent-grafts, as they did not add additional information to the visualization.

Multislice CT angiography in abdominal aortic aneurysm treated with endovascular stent grafts: evaluation of 2D and 3D visualisations

Endovascular repair of abdominal aortic aneurysms has been introduced into the clinical practice for more than a decade and has been confirmed to be an effective alternative to conventional open surgery, especially in patients with co-morbid medical conditions. Helical CT angiography is the preferred imaging method in the follow-up of endovascular repair. Recent introduction of multislice CT scanners has augmented its diagnostic role in this area. Diagnostic value of multlislice CT has been complemented by a series of 3D post-processings, which assist vascular surgeons in accurately assessing the effect of endovascular repair by providing additional information when compared to conventional 2D axial images. These reconstructions include multiplanar reformation, curved multiplanar reconstruction, shaded surface display, maximum intensity projection, volume rendering and virtual endoscopy. This article aims to demonstrate the generation of these 2D/3D reconstructions based on multislice CT data acquired from a group of patients with abdominal aortic aneurysm following endovascular repair. A brief introduction of generating each reconstruction was provided; potential clinical applications of each reconstruction were briefly discussed. Images were presented in a dynamic format with the aim of allowing the reader to easily understand the post-processing of these reconstructions.

Multislice CT angiography in aortic stent grafting: Relationship between image noise and body mass index

PURPOSE

To investigate the correlation between image noise and body mass index (BMI) in multislice CT angiography (MSCT) for patients with abdominal aortic aneurysm (AAA) treated with endovascular stent grafts.

MATERIALS AND METHODS

Seventeen patients who underwent MSCT following endovascular repair of AAA were included in the study. Image noise (standard deviation of the CT attenuation: S.D.) and signal to noise ratio (SNR) were plotted against BMI to demonstrate the correlation using a linear regression method. Image quality of 3D reconstructions was correlated to the SNR and BMI.

RESULTS

The r-value of linear regression between S.D. and BMI was 0.578 (p<0.05), 0.835 and 0.802 (p<0.001), respectively, at the level of renal artery, aortic aneurysm and common iliac artery. The r-value of linear regression between SNR and BMI was 0.332, 0.516 and 0.552 (p<0.05), respectively, at above three levels. Image quality of 3D reconstructions was compromised in five patients and diagnosis was affected in two patients with BMI more than 30.

CONCLUSION

A significant correlation was observed between image noise and BMI in MSCT angiography of endovascular repair of AAA. Our findings are valuable for optimisation of MSCT angiography scanning protocols and reduction of radiation dose in MSCT examinations.