Assessment of VIE image quality using helical CT angiography: in vitro phantom study

Optimization of computed tomography pulmonary angiography protocols using 3D printed model with simulation of pulmonary embolism

Background

Three-dimensional (3D) printing has been shown to accurately replicate anatomical structures and pathologies in complex cardiovascular disease. Application of 3D printed models to simulate pulmonary arteries and pulmonary embolism (PE) could assist development of computed tomography pulmonary angiography (CTPA) protocols with low radiation dose, however, this has not been studied in the literature. The aim of this study was to investigate optimal CTPA protocols for detection of PE based on a 3D printed pulmonary model.

Methods

A patient-specific 3D printed pulmonary artery model was generated with thrombus placed in both main pulmonary arteries to represent PE. The model was scanned with 128-slice dual-source CT with slice thickness of 1 and 0.5 mm reconstruction interval. The tube voltage was selected to range from 70, 80, 100 to 120 kVp, and pitch value from 0.9 to 2.2 and 3.2. Quantitative assessment of image quality in terms of signal-to-noise ratio (SNR) was measured in the main pulmonary arteries and within the thrombus regions to determine the relationship between image quality and scanning protocols. Both two-dimensional (2D) and 3D virtual intravascular endoscopy (VIE) images were generated to demonstrate pulmonary artery and thrombus appearances.

Results

PE was successfully simulated in the 3D printed pulmonary artery model. There were no significant differences in SNR measured in the main pulmonary arteries with 100 and 120 kVp CTPA protocols (P>0.05), regardless of pitch value used. SNR was significantly lower in the high-pitch 3.2 protocols when compared to other protocols using 70 and 80 kVp (P<0.05). There were no significant differences in SNR measured within the thrombus among the 100 and 120 kVp protocols (P>0.05). For low dose 70 and 80 kVp protocols, SNR was significantly lower in the high-pitch of 3.2 protocols than that in other protocols with different pitch values (P<0.01). 2D images showed the pulmonary arteries and thrombus clearly, while 3D VIE demonstrated intraluminal appearances of pulmonary wall and thrombus in all protocols, except for the 70 kVp and pitch 3.2 protocol, with visualization of thrombus and pulmonary artery wall affected by artifact associated with high image noise. Radiation dose was reduced by up to 80% when lowering kVp from 120 to 100 and 80 kVp with use of 3.2 high-pitch protocol, without significantly affecting image quality.

Conclusions

Low-dose CT pulmonary angiography can be achieved with use of low kVp (80 and 100) and high-pitch protocol with significant reduction in radiation dose while maintaining diagnostic images of PE. Use of high pitch, 3.2 in 70 kVp protocol should be avoided due to high image noise and poorer quality.

Synchrotron radiation computed tomography versus conventional computed tomography for assessment of four types of stent grafts used for endovascular treatment of thoracic and abdominal aortic aneurysms

Background

To determine the accuracy of synchrotron radiation computed tomography (CT) for measurement of stent wire diameters for in vitro simulation of endovascular aneurysm repair by four different types of stent grafts when compared to conventional CT images.

Methods

This study was performed using an aorta model with implantation of four aortic stent grafts for endovascular treatment of thoracoabdominal and abdominal aortic aneurysms. The aorta model was scanned using synchrotron radiation CT with beam energies ranging from 60 to 90 keV with 10 keV increment at each scan and spatial resolution of 41.6 µm per pixel. Stent wire diameters were measured at the top and body regions of each stent graft based on 2-dimensional (2D) axial and 3-dimensional (3D) reconstruction images, with measurements compared to those obtained from 128-slice CT images which were acquired with slice thickness of 0.5 mm.

Results

Synchrotron radiation CT images clearly demonstrated stent graft details with accurate assessment of stent wire diameters, with measurements at the top of stent grafts (between 0.32±0.02 and 0.47±0.02 mm) similar to the actual diameters (between 0.32±0.01 and 0.48±0.01 mm) when the beam energies of 70 and 80 keV were used, regardless of the types of stent grafts assessed. A beam energy of 60 keV resulted in stent wires thicker than the actual sizes, although this did not reach statistical significance (P=0.07-0.29), while the beam energy of 90 keV led to stent wires smaller than the actual sizes at the top (P=0.16) and body region (P=0.02) of stent grafts on 2D axial images. The stent wire sizes measured at the body region of stent grafts on 3D synchrotron radiation images (between 0.19±0.02 and 0.43±0.02 mm) were significantly smaller than the actual diameters (P=0.02-0.04). Stent wires were overestimated on conventional CT images with diameters more than 2-fold larger than the actual sizes (P=0.007-0.03) at both top and body regions of all four stent grafts.

Conclusions

This study further confirms the accuracy of high-resolution synchrotron radiation CT in image visualization and size measurement of different aortic stent grafts with measured wire diameters similar to the actual ones, thus allowing for more accurate assessment of stent wire details for endovascular repair of aortic aneurysms.

Use of Synchrotron Radiation to Accurately Assess Cross-Sectional Area Reduction of the Aortic Branch Ostia Caused by Suprarenal Stent Wires

PURPOSE

To compare in vivo the use of synchrotron radiation to computed tomography angiography (CTA) for the measurement of cross-sectional area (CSA) reduction of the aortic branch ostia caused by suprarenal stent-graft wires.

METHODS

This study was performed with a Zenith stent-graft placed in a phantom of the human aorta to simulate treatment of abdominal aortic aneurysm. Synchrotron radiation scans were performed using beam energies between 40 and 100 keV and spatial resolution of 19.88 μm per pixel. CSA reduction of the aortic branch ostia by suprarenal stent wires was calculated based on these exposure factors and compared with measurements from CTA images acquired on a 64-row scanner with slice thicknesses of 1.0, 1.5, and 2.0 mm.

RESULTS

Images acquired with synchrotron radiation showed <10% of the CSA occupied by stent wires when a single wire crossed a renal artery ostium and <20% for 2 wires crossing a renovisceral branch ostium. The corresponding areas ranged from 24% to 25% for a single wire and from 40% to 48% for double wires crossing the branch ostia when measured on CT images. The stent wire was accurately assessed on synchrotron radiation with a diameter between 0.38±0.01 and 0.53±0.03 mm, which is close to the actual size of 0.47±0.01 mm. The wire diameter measured on CT images was greatly overestimated (1.15±0.01 to 1.57±0.02 mm).

CONCLUSION

CTA has inferior spatial resolution that hinders accurate assessment of CSA reduction. This experiment demonstrated the superiority of synchrotron radiation over CTA for more accurate assessment of aortic stent wires and CSA reduction of the aortic branch ostia.

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 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.

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

OBJECTIVE

To investigate the optimal scanning protocol for multislice computed tomography angiography (MSCT) in pre-aortic stent grafting observed with virtual intravascular endoscopy (VIE).

MATERIALS AND METHODS

The study was performed on a human abdominal aortic phantom which was housed in a perspex container, filled with contrast medium having CT attenuation similar to that used in the patient's abdominal CT scan. A series of scans were performed on a four-slice multislice CT scanner with the scanning protocols as follows: section thickness of 1.3, 3.2 and 6.5 mm, pitch value of 0.875, 1.25 and 1.75 with reconstruction intervals of 50% overlap. The degree of stair-step artifacts was measured at three different locations, superior mesenteric artery (SMA), renal ostium and the normal abdominal aorta. Standard deviation (S.D.) of the signal intensity measured on surface shaded images was used to determine the image quality. Radiation dose was also recorded in each scanning protocol.

RESULTS

The VIE images showed that image quality was not dependent on pitch and section thickness in the visualization of renal ostium and SMA, whereas it was dependent on these two factors at the level of the normal aorta (p<0.05). It was noticed that when section thickness reached 6.5 mm the SMA and renal ostia became distorted. Radiation dose measured in 1.3 mm protocols was significantly higher that those measured in other section thicknesses (p<0.05).

CONCLUSION

The scanning protocol of section thickness 3.2 mm, pitch 1.25 with a reconstruction interval of 1.6 mm was recommended as it allows optimal visualization of VIE images of aortic ostia, generation of fewer artifacts and less radiation dose.

Effect of Suprarenal Stent Struts on the Renal Artery with Ostial Calcification Observed on CT Virtual Intravascular Endoscopy

OBJECTIVES

The behaviour of stent struts crossing the renal ostia and their effect on renal ostia configuration is not well understood. The study aims to investigate whether suprarenal stent struts affect the morphological change of the renal artery with ostial calcification observed on CT virtual intravascular endoscopy.

METHODS

Nine patients with abdominal aortic aneurysms undergoing suprarenal fixation of stent grafts were included in the study. All patients received a Zenith endovascular graft with uncovered suprarenal components placed above the renal arteries. Renal ostial calcification and configuration of stent wires crossing the renal ostium were characterized in each patient and maximal transverse and longitudinal diameters of the renal ostia were measured on virtual endoscopy pre- and post-stent grafting.

RESULTS

There were altogether 17 renal ostia assessed with one patient having atrophic left kidney and no renal ostium being observed. Ostial calcification was found in five of the left renal ostia and five of the right renal ostia with one patient having bilateral ostial calcification. There was no significant difference between the renal ostial diameters measured pre- and post-stent grafting (p>0.05). Suprarenal stent struts were found to cross the renal ostia in various configurations observed on virtual endoscopy. All of the renal arteries were patent on follow-up CT scans after suprarenal fixation without stenosis or occlusion being observed. One patient with atrophic left renal artery developed renal failure following suprarenal stent grafting and received renal dialysis, while in the remaining cases median serum creatinine level did not change significantly.

CONCLUSIONS

Suprarenal stent struts did not significantly affect the renal ostia with ostial calcification in terms of the diameter measurements and renal function. Further studies deserve to investigate the long-term effect of stent struts on the renal artery in terms of cross-sectional area reduction caused by stent wires and ostial calcification.

Multislice CT Virtual Intravascular Endoscopy for Abdominal Aortic Aneurysm Stent Grafts

PURPOSE

To investigate the optimal scanning protocols of multislice computed tomographic (CT) angiography in aortic stent graft placement observed on virtual intravascular endoscopy (VIE).

MATERIALS AND METHODS

A human aorta phantom was built with a commercial aortic stent graft placed in situ. The phantom was housed in a perspex container and filled with contrast medium with CT attenuation similar to that used in the patient's abdominal scanning. CT was performed with a four-slice multislice CT scanner with section thickness of 1.3 mm, 2 mm, and 3.2 mm, pitch of 0.75, 1, and 1.5, and reconstruction interval of 50% overlap and no overlap. Stair-step artifacts were quantified by measuring the SD of signal intensity on surfaced shaded VIE images in three different locations: superior mesenteric artery (SMA), renal ostium, and aortic aneurysm.

RESULTS

Image quality of VIE images was independent of section thickness and pitch values in the level of renal ostium and aortic aneurysm (P >.05), whereas it was determined by the section thickness and pitch in the level of SMA (P <.05). Aortic branch origin became irregular or distorted when section thickness increased to 3.2 mm or pitch reached 1.5.

CONCLUSION

A scanning protocol of section thickness of 2 mm, pitch 1, and reconstruction interval of 1 mm is recommended in aortic stent graft placement because it allows fewer stair-step artifacts and better visualization of the aortic stent wires observed on VIE.

Cross-sectional area reduction of the aortic ostium by suprarenal stent wires: in vitro phantom study by CT virtual angioscopy

The study aims to investigate the reduction of cross-sectional area of the aortic ostium by the presence of aortic stent wires observed using CT virtual angioscopy in an aorta phantom. A human aorta phantom was built with a commercial stent graft placed in situ to simulate a repaired aortic aneurysm. Virtual angioscopic images of the aortic ostium and stent wires were generated in the locations of renal arteries, superior mesenteric artery and corresponding cross-sectional area reduction caused by stent wires was measured by virtual angioscopy in various scanning parameters. Our study showed that cross-sectional area reduction of the aortic ostium was determined by the diameter of renal ostium and stent wires, as well as the number of stent wires crossing the aortic ostium.