Prospective versus retrospective ECG gating for dual source CT of the coronary stent: Comparison of image quality, accuracy, and radiation dose

Objective

To compare image quality, diagnostic accuracy and radiation dose of prospective and retrospective electrocardiogram (ECG) gated dual source computed tomography (DSCT) for the evaluation of the coronary stent, using conventional coronary angiography (CA) as a standard reference.

Design, setting and patients

Sixty patients (heart rates ≤70 bpm) with previous stent implantation who were scheduled for CA were divided in two groups, receiving either prospective or retrospective ECG gated DSCT separately. Two reviewers scored coronary stent image quality and evaluated stent lumen.

Results

There was no significant difference in image quality between the two groups. In the prospective group, there were 86.4% (51/59) stents with interpretable images, in the retrospective group, there were 87.5% (49/56) stents with interpretable images. Image quality was not influenced by age, body mass index or heart rate in either group, but heart rate variability had a weak impact on the image quality of the prospective group. Image noise was higher in the prospective group, but this difference reached statistical significance only by using a smooth kernel reconstruction. Per-stent based sensitivity, specificity, and positive and negative predictive value were 100%, 84.1%, 68.2%, and 100%, respectively, in the prospective CT angiography group and 94.4%, 86.8%, 77.3%, and 97.1%, respectively, in the retrospective CT angiography group. There was a significant difference in the effective radiation dose between the two groups, mean effective dose in the prospective and retrospective group was 2.2 ± 0.5 mSv (1.5-3.2 mSv) and 14.6 ± 3.3 mSv (10.0-20.4 mSv) (p < .001) respectively.

Conclusions

Compared with retrospective CT angiography, prospective CT angiography has a similar performance in assessing coronary stent patency, but a lower effective dose in selected patients with regular heart rates ≤70 bpm.     

64-slice multidetector coronary CT angiography: in vitro evaluation of 68 different stents

The purpose of this study was to test a large sample of different coronary artery stents using four image reconstruction approaches with respect to lumen visualization, lumen attenuation, and image noise in 64-slice multidetector-row computed tomography (MDCT) in vitro and to provide a catalogue of currently used coronary artery stents when imaged with state-of the-art MDCT. We examined 68 different coronary artery stents (57 stainless steel, four cobalt-chromium, one cobalt-alloy, two nitinol, four tantalum) in a coronary artery phantom (vessel diameter 3 mm, intravascular attenuation 250 HU, extravascular density −70). Stents were imaged in axial orientation with standard parameters: 32x0.6 collimation, pitch 0.24, 680 mAs, 120 kV, rotation time 0.37 s. Four different image reconstructions were obtained with varying convolution kernels and section thicknesses: (1) soft, 0.6 mm, (2) soft, 0.75, (3) medium soft, 0.6, and (4) stent-optimized sharp, 0.6. To evaluate visualization characteristics of of the stent, the lumen diameter, intraluminal density and noise were measured. The high-resolution kernel offered significantly better average lumen visualization (57% ±10%) and more realistic lumen attenuation (222 HU ±66 HU) at the expense of increased noise (15.3 HU ±3.7 HU) compared with the soft and medium-soft CT angiography (CTA) protocol (p<0.001 for all). Stents with a lumen visibility of more than 66% were: Arthos pico, Driver, Flex, Nexus2, S7, Tenax complete, Vision (all 67%), Symbiot, Teneo (70%), and Radius (73%). Only ten stents showed a lumen visibility of less than 50%. Stent lumen visibility largely varies depending on the stent type. Even with the improved spatial resolution of 64-slice CT, a stent-optimized kernel remains beneficial for stent visualization when compared with the standard medium-soft CTA protocol. Using 64-slice CT and high-resolution kernel, the majority of stent products show a lumen visibility of more than 50% of the stent diameter.     

Performance of dual source versus 256-slice multi-slice CT in the evaluation of 16 coronary artery stents

Introduction

Invasive coronary angiography is the reference method for identification of in-stent restenosis (ISR) bearing the disadvantages of high costs and invasiveness. New approaches like dual-source CT (DSCT) and 256-multi-slice CT (256-MSCT) may potentially be the future methods of choice to reliably exclude ISR in patients with low or intermediate risk of restenosis.We sought to compare the performance of DSCT and 256-MSCT for the in vitro assessment of stent lumen diameter and basic scan parameters in stents of various diameters and designs.

Materials and Methods

In 16 coronary artery stents we evaluated relative in-stent lumen diameter, attenuation, noise, attenuation-/signal-to-noise ratio (ANR/SNR) and radiation dose (CTDI_vol) in an acknowledged coronary vessel in vitro phantom (iodine-filled plastic tubes) with DSCT (Siemens, SOMATOM Definition, collimation = 2 × 64 × 0.6 mm, pitch = 0.26, current = 400 mAs/rot, voltage = 120 kV, tube-rotation-time = 330 ms) and 256-MSCT (Philips Brilliance, iCT, tube collimation = 2 × 128 × 0.625 mm, pitch = 0.18, current = 800 mAs_eff, voltage = 120 kV, tube-rotation-time = 270 ms). Diameter analysis was conducted with the observer-independent full-width-at-half-maximum (FWHM) technique.

Results

DSCT and 256-MSCT revealed similar stent lumen diameters (50.7 ± 7.2% vs. 50.8 ± 7.4%, p = 0.98). Attenuation (−19 ± 25 HU vs. 54 ± 29 HU), ANR (−0.9 ± 1.2 vs. 2.9 ± 1.8) and SNR (12.1 ± 2.4 vs. 17.4 ± 1.9) were better in the DSCT (all p < 0.001) at the expense of significantly higher radiation doses (CTDI_vol = 87 vs. 51 mGy, p < 0.01). Noise was comparable (21 ± 2 HU vs. 20 ± 2 HU, p = n.s.). Only stents with a diameter >3 mm allowed sufficient stent lumen assessment in both scanners and showed a relative lumen diameter of 60–66%.

Conclusions

The measured stent lumen diameter and image noise were similar in both scanners. Yet the DSCT offered a more truthful stent lumen visualization at the cost of higher radiation dose.Applying the FWHM approach only stents with a diameter >3 mm offered sufficient stent lumen assessment.     

Update on multidetector coronary CT angiography of coronary stents: in vitro evaluation of 29 different stent types with dual-source CT

The aim of this study was to test a large sample of the latest coronary artery stents using four image reconstruction approaches with respect to lumen visualization, lumen attenuation, and image noise in dual-source multidetector row CT (DSCT) in vitro and to provide a CT catalogue of currently used coronary artery stents. Twenty-nine different coronary artery stents (19 steel, 6 cobalt-chromium, 2 tantalum, 1 iron, 1 magnesium) were examined in a coronary artery phantom (vessel diameter 3 mm, intravascular attenuation 250 HU, extravascular density −70 HU). Stents were imaged in axial orientation with standard parameters: 32 × 0.6 collimation, pitch 0.24, 400 mAs, 120 kV, rotation time 0.33 s. Image reconstructions were obtained with four different convolution kernels (soft, medium-soft, standard high-resolution, stent-dedicated). To evaluate visualization characteristics of the stent, the lumen diameter, intraluminal density, and noise were measured. The stent-dedicated kernel offered best average lumen visualization (54 ± 8.3%) and most realistic lumen attenuation (222  ± 44 HU) at the expense of increased noise (23.9 ± 1.9 HU) compared with standard CTA protocols (p < 0.001 for all). The magnesium stent showed the least artifacts with a lumen visibility of 90%. The majority of stents (79%) exhibited a lumen visibility of 50–59%. Less than half of the stent lumen was visible in only six stents. Stent lumen visibility largely varies depending on the stent type. Magnesium is by far more favorable a stent material with regard to CT imaging when compared with the more common materials steel, cobalt-chromium, or tantalum. The magnesium stent exhibits a lumen visibility of 90%, whereas the majority of the other stents exhibit a lumen visibility of 50–59%. David Maintz and Matthias Burg contributed equally to this publication.     

Multislice CT angiography assessment of left coronary artery: correlation between bifurcation angle and dimensions and development of coronary artery disease

Purpose

To investigate the relationship between left coronary bifurcation and dimensional changes and development of coronary artery disease using multislice CT angiography.

Materials and methods

30 patients (18 men, 12 women, mean age, 56 years ± 8) suspected of coronary artery disease undergoing 64- and 256-slice CT angiography were included in the study. Left bifurcation angle and left coronary diameter were measured to determine the relationship between angulation and plaque formation and subsequent dimensional changes.

Results

Plaques were present in the left coronary artery in 22 patients with variable angulations and dimensional changes. The mean bifurcation angle between left anterior descending and left circumflex arteries was measured 89.1° ± 13.1° (range, 55.3°, 134.5°) among all patients. The mean bifurcation angle measured in patients with normal and diseased left coronary artery was 75.5° ± 19.8° (range, 60°, 96.1°), and 94° ± 19.7° (range, 55.3°, 134.5°), respectively, with significant difference between these two groups (p = 0.02). Similarly, there is a significant difference in the mean diameters of left anterior descending and left circumflex between patients with normal and diseased left coronary artery (p < 0.001), which were measured 2.8 ± 0.3 mm (range, 2.2, 3.2 mm) and 2.1 ± 0.4 mm (range, 1.9, 2.9 mm) for the normal left coronary arteries, 4.0 ± 0.8 mm (range, 2.5, 6.1 mm) and 2.9 ± 0.5 mm (range, 1.6, 3.9 mm) for the diseased left coronary arteries, respectively.

Conclusion

There is a direct correlation between left bifurcation angle and dimensional changes and formation of plaques. Multislice CT angiography can be used to provide relevant features of left coronary atherosclerosis.     

Imaging of coronary artery stents using multislice computed tomography: in vitro evaluation

The aim of this study was to evaluate imaging features of different coronary artery stents during multislice CT Angiography (MSCTA). Nineteen stents made of varying material (steel, nitinol, tantalum) and of varying stent design were implanted in plastic tubes with an inner diameter of 3 mm to simulate a coronary artery. The tubes were filled with iodinated contrast material diluted to 200 Hounsfield units (HU), closed at both ends and positioned in a plastic container filled with oil (–70 HU). The MSCT scans were obtained perpendicular to the stent axes (detector collimation 4×1 mm, table feed 2 mm/rotation, 300 mAs, 120 kV). Axial images and multiplanar reformations were evaluated regarding artifact size, lumen visibility, and intraluminal attenuation values. Artifacts characterized by artifactual thickening of the stent struts leading to apparent reduction in the lumen diameter and increased intraluminal attenuation values were observed in all cases. The stent lumen was totally obscured in the Wiktor stent, the Wallgraft stent, and the Nir Royal stent. Partial residual of the stent lumen could be visualized in all other utilized stent products (artificial lumen reductions ranged from 62% in the V-Flex stent to 94% in the Bx Velocity stent). Parts of the stent lumen can be visualized in most coronary artery stents; however, detectability of in-stent stenoses remains to be evaluated for each stent type. Electronic Publication     

Cardiac CT angiography after coronary artery surgery in children using 64-slice CT scan

Objective

The purpose of this study was to compare the diagnostic accuracy of 64-slice CT with that of invasive angiography in the detection of graft and/or coronary angioplasty stenosis in children who had undergone coronary artery surgery.

Population and methods

Fifteen consecutive children (8 male and 7 female; age 9.2 ± 6.1 years) underwent 64-slice CT because of chest pain or ECG changes mean 4.8 ± 3.7 years after surgical coronary artery surgery; 10 patients had coronary angioplasty using a patch from the saphenous vein, four had mammary artery bypass, and one had saphenous vein bypass. Six main segments of the coronary arteries and all the bypass graft considered as a single segment were analyzed and compared with invasive angiography used as the reference standard.

Results

CT correctly identified the four children with coronary angioplasty and mammary graft lesions that were confirmed by conventional angiography: one patient had a significant stenosis (>50% stenosis) at the mammary bypass graft anastomosis site; three other had non-significant stenosis (<50% stenosis) including a mild lesion of the saphenous vein patch in two patients and a mild lesion at the anastomosis site of the mammary bypass in one. All segments identified as normal by CT in the other 11 children were also found to be normal by conventional angiography.

Conclusion

In centers expert in this technique, 64-slice CT scanning is a promising, rapid, and useful diagnostic technique for evaluating both coronary angioplasty and bypass graft lesions in children who had undergone coronary artery surgery.     

64-slice computed tomography assessment of coronary artery stents: a phantom study

Purpose: To compare the use of a new 64-slice computed tomography (CT) scanner with 16-slice CT in the visualization of coronary artery stent lumen.

Material and Methods: Eight different coronary artery stents, each with a diameter of 3 mm, were placed in a static chest phantom. The phantom was positioned in the CT gantry at an angle of 0° and 45° towards the z-axis and examined with both a 64-slice and a 16-slice CT scanner. Effective slice thickness was 0.6 mm with 64-slice CT and 1 mm with 16-slice CT. A reconstruction increment of 0.3 mm was applied in both scanners. Image quality was assessed visually using a 5-point grading scale. Stent diameters were measured and compared using paired Wilcoxon tests.

Results: Artificial lumen reduction was significantly less with 64-slice than with 16-slice CT. Average visible stent lumen was 53.4% using 64-slice CT and 47.5% with 16-slice MSCT. Most severe artifacts were seen in stents with radiopaque markers. Using 64-slice CT, image noise increased by approximately 30% due to thinner slice thickness.

Conclusion: Improved spatial resolution of 64-slice CT resulted in superior assessment of coronary artery stent lumen compared to 16-slice CT. However, a relevant part of the stent lumen is still not assessable with multi-slice CT.     

In vitro imaging of coronary artery stents: Are there differences between 16- and 64-slice CT scanners?

Purpose

To compare the performance of 64-slice with 16-slice CT scanners for the in vitro evaluation of coronary artery stents.

Methods and materials

Twelve different coronary artery stents were placed in the drillings of a combined heart and chest phantom, which was scanned with a 16- and 64-slice CT scanner. Coronal reformations were evaluated for artificial lumen narrowing, intraluminal attenuation values, and false widening of the outer stent diameter as an indicator of artifacts outside the stent.

Results

Mean artificial lumen narrowing was not significantly different between the 16- and 64-slice CT scanner (44% versus 39%; p = 0.408). The differences between the Hounsfield Units (HU) measurements inside and outside the stents were significantly lower (p = 0.001) with 64- compared to 16-slice CT. The standard deviation of the HU measurements inside the stents was significantly (p = 0.002) lower with 64- than with 16-slice CT. Artifacts outside the stents were not significantly different between the scanners (p = 0.866).

Conclusion

Visualization of the in-stent lumen is improved with 64-slice CT when compared with 16-slice CT as quantified by significantly lesser intraluminal image noise and less artificial rise in intraluminal HU measurement, which is the most important parameter for the evaluation of stent patency in vivo.     

High-resolution ex vivo imaging of coronary artery stents using 64-slice computed tomography—initial experience

The aim of the study was to evaluate the potential of new-generation multi-slice computed tomography (CT) scanner technology for the delineation of coronary artery stents in an ex vivo setting. Nine stents of various diameters (seven stents 3 mm, two stents 2.5 mm) were implanted into the coronary arteries of ex vivo porcine hearts and filled with a mixture of an iodine-containing contrast agent. Specimens were scanned with a 16-slice CT (16SCT) machine; (Somatom Sensation 16, Siemens Medical Solutions), slice thickness 0.75 mm, and a 64-slice CT (64SCT, Somatom Sensation 64), slice-thickness 0.6 mm. Stent diameters as well as contrast densities were measured, on both the 16SCT and 64SCT images. No significant differences of CT densities were observed between the 16SCT and 64SCT images outside the stent lumen: 265±25HU and 254±16HU (P=0.33), respectively. CT densities derived from the 64SCT images and 16SCT images within the stent lumen were 367±36HU versus 402±28HU, P<0.05, respectively. Inner and outer stent diameters as measured from 16SCT and 64SCT images were 2.68±0.08 mm versus 2.81±0.07 mm and 3.29±0.06 mm versus 3.18±0.07 mm (P<0.05), respectively. The new 64SCT scanner proved to be superior in the ex vivo assessment of coronary artery stents to the conventional 16SCT machine. Increased spatial resolution allows for improved assessment of the coronary artery stent lumen.     

The detection of coronary stiffness in cardiac allografts using MR imaging

Objective

To test the hypothesis that biomechanical changes are quantitatively related to morphological features of coronary arteries in heart transplant (HTx) recipients.

Materials and methods

With IRB approval, three-dimensional (3D) magnetic resonance (MR) angiography and two-dimensional (2D) black-blood stead-state free precession (SSFP) MR imaging were performed to image coronary arteries of 36 HTx patients. Contours of coronary wall were manually drawn. For each coronary segment, coronary wall thickness, wall area, lumen area (in systole and diastole) were acquired. Coronary distensibility index (CDI) and the percent of the coronary wall occupying the vessel area (PWOV) were calculated.

Results

There are totally 98 coronary segments eligible for quantitative analysis from 27 HTx patients. The CDI is 4.90 ± 2.44 mmHg⁻¹. The mean wall thickness is 1.49 ± 0.24 mm and the PWOV is 74.6% ± 7.5%. CDI has moderate correlations with wall thickness (r = −0.531, P < 0.001) and with PWOV (R = −0.435, P < 0.001).

Conclusions

Detected with coronary MR imaging, CDI is quantitatively correlated with the morphological features of the coronary artery in HTx patients. Coronary stiffness has the potential to become an alternative imaging biomarker for the quantitative assessment of the status of cardiac allografts.     

Diagnostic performance of prospectively ECG triggered versus retrospectively ECG gated 64-slice computed tomography coronary angiography in a heterogeneous patient population

Objective

To compare diagnostic performance and applicability of prospectively versus retrospectively gated 64-slice computed tomography coronary angiography (pro-CTCA vs. retro-CTCA) in a heterogeneous patient population compared to invasive coronary angiography.

Methods

77 patients referred to an ECG-gated-CT of the chest were retrospectively included. Pro-CTCA was applied, whenever possible, alternatively retro-CTCA was performed. All coronary artery segments ≥1.5 mm were analysed and image quality was assessed.

Results

In 39 patients retro-CTCA and in 38 patients pro-CTCA was applied, mean heart rate (HR) was 69.5 ± 9.1 min⁻¹ and 62.8 ± 5.9, respectively. For a stenosis ≥50% segment-based (patient-based) analysis revealed a sensitivity, specificity, positive (PPV) and negative predictive value (NPV) of 97%, 98%, 71%, 100% (91%, 82%, 67%, 96%) using retro-CTCA and 94%, 97%, 75%, 99% (93%, 96%, 93%, 96%) using pro-CTCA. Sensitivity and NPV increased in the pro-CTCA group in patients with a HR < 65. Vessel-based analysis showed lower diagnostic performance for the right coronary artery (RCA) using pro-CTCA, which increased when HR < 65. Image quality did not differ significantly in both groups.

Conclusions

Prospectively triggered CTCA in a heterogeneous patient group has a very high diagnostic accuracy and image quality, when used in HR ≤ 65. A low HR is of special importance for the evaluation of the RCA.     

CT angiography of various superficial femoral artery stents: an in vitro phantom study

Purpose

To evaluate CT reconstruction parameters to improve stent lumen visualization in vitro.

Material and methods

12 latest superficial femoral artery (SFA) stents were placed in a vessel phantom (diameter 4.7 mm, intravascular attenuation 250 HU, extravascular density 50 HU). Stents were imaged with a 128-slice scanner (SOMATOM Definition Flash, Siemens, Germany) with standard parameters: 120 kV, 200 mAs, collimation 128 mm × 0.6 mm. Different reconstruction parameters were evaluated: B26f, B30f, B45f, B46f and B60f kernel; slice thickness of 0.6, 2.0 and 5.0 mm. To measure visualization characteristics, stent lumen diameter and intraluminal attenuation were assessed.

Results

Best stent lumen visualization could be obtained using the B46f kernel (p < 0.001). The visible stent lumen ranged from 66.4% to 83.3% with a mean diameter of 77.7 ± 4.6%. Nitinol stents showed a significant improved lumen visibility compared to the cobalt–chromium stent (p = 0.02). The most realistic lumen attenuation was achieved using the B46f kernel with a mean attenuation of 259.3 ± 8.9 HU. The visible lumen diameter in protocols with 5 mm slice thickness was significantly lower (70.0 ± 4.9%) compared to thinner slices (p < 0.001).

Conclusion

CTA of SFA stents should be reconstructed with a slice thickness of 2.0 mm and a B46f kernel to achieve best image quality and to become more sensitive to exclude instent restenosis.     

What is the best contrast injection protocol for 64-row multi-detector cardiac computed tomography?

Objective

To determine the optimal contrast injection protocol for 64-MDCT coronary angiography.

Materials and methods

One hundred and fifty consecutive patients scheduled to undergo retrospectively electrocardiographically gated 64-MDCT. Each 30 patients were assigned to use a different contrast protocol: group 1: uniphasic protocol (contrast injection without saline flush); group 2: biphasic protocol (contrast injection with saline flush); group 3A, 3B and 3C: triphasic protocol (contrast media + different saline diluted contrast media + saline flush). Image quality scores and artifacts were compared and evaluated on both transaxial and three-dimensional coronary artery images among each contrast protocol.

Results

Among the triphasic protocol groups, group 3A (30%:70% contrast media-saline mixture was used in second phase) used the least contrast media and had the least frequency of streak artifacts, but there were no significant differences in coronary artery attenuation, image quality, visualization right and left heart structures. Among the uniphasic protocol group (group 1), biphasic protocol group (group 2) and triphasic protocol subgroup (group 3A), there were no significant differences in image quality scores of coronary artery (P = 0.18); uniphasic protocol group had the highest frequency of streak artifacts (20 cases) (P < 0.05) and had the most amount contrast media (67.0 ± 5.3 ml); biphasic protocol group had the least amount of contrast media (59.9 ± 4.9 ml) (P < 0.05) and had the highest attenuation of left main coronary artery and right coronary artery (P < 0.01), but had the least amount of clear visualization right heart structure (6 cases); triphasic protocol group (group 3A) had the most amount of clear visualization right heart structures (29 cases) were the most among the three groups (P < 0.05).

Conclusion

Biphasic protocol are superior to the traditional uniphasic protocols for using the least total contrast media, having the least Streak artifacts and without image quality degradation. However, it is also important to visualize the right atrium and ventricle, so triphasic protocol (30%:70% contrast media-saline mixture was used in second phase) should be used for 64-MDCT coronary CT angiography.     

Prevalence of myocardial bridging detected with 64-slice multidetector coronary computed tomography angiography in asymptomatic adults

Objective

Myocardial bridging is a congenital condition in which a segment of an epicardial artery has an intramural course within the myocardium. The aim of the present study was to evaluate the prevalence of myocardial bridging and the ability of 64-slice coronary computed tomography angiography to identify myocardial bridging in asymptomatic adults.

Methods

One hundred sixty-nine consecutive asymptomatic subjects underwent 64-row multidetector computed tomography (MDCT) of the coronary arteries. Two experienced CT radiologists identified myocardial bridging >1 mm in thickness, by consensus. We examined the frequency of myocardial bridging and evaluated the length, thickness, and coronary wall lesions.

Results

Myocardial bridges were found in 28 (17%) of 165 subjects. Twenty-one subjects (75%) had 1 bridge and 7 subjects (25%) had 2, for a total of 35 myocardial bridges. Twenty-one bridges (60%) were located in the left anterior descending, 8.5% in the diagonal branch, and 2.8% in the circumflex arteries. The segment beneath the myocardial bridge was always free of coronary wall plaques, but the arterial segment proximal to it had significant coronary wall plaques in 24 cases (68.6%).

Conclusion

We found that the incidence of myocardial bridging in asymptomatic adults is 7%, which is in agreement with some pathologic studies in the literature. Our study shows that MDCT of the coronary arteries is a reliable and noninvasive technique, which can accurately locate the site of myocardial bridging, and measure its thickness, course, and length.     

Regional variance of visually lossless threshold in compressed chest CT images: lung versus mediastinum and chest wall

Purpose

The purpose of this study was to characterize the heartbeat-related displacement of the thoracic aorta in patients with chronic aortic dissection type B (CADB).

Materials and methods

Electrocardiogram-gated computed tomography angiography was performed during inspiratory breath-hold in 11 patients with CADB: Collimation 16 mm × 1 mm, pitch 0.2, slice thickness 1 mm, reconstruction increment 0.8 mm. Multiplanar reformations were taken for 20 equidistant time instances through both ascending (AAo) and descending aorta (true lumen, DAoT; false lumen, DAoF) and the vertex of the aortic arch (VA). In-plane vessel displacement was determined by region of interest analysis.

Results

Mean displacement was 5.2 ± 1.7 mm (AAo), 1.6 ± 1.0 mm (VA), 0.9 ± 0.4 mm (DAoT), and 1.1 ± 0.4 mm (DAoF). This indicated a significant reduction of displacement from AAo to VA and DAoT (p < 0.05). The direction of displacement was anterior for AAo and cranial for VA.

Conclusion

In CADB, the thoracic aorta undergoes a heartbeat-related displacement that exhibits an unbalanced distribution of magnitude and direction along the thoracic vessel course. Since consecutive traction forces on the aortic wall have to be assumed, these observations may have implications on pathogenesis of and treatment strategies for CADB.     

MDCT angiography assessment of renal artery in-stent restenosis: Can we reduce the radiation exposure burden? A feasibility study

Aim

We explored the feasibility of renal artery multidetector computed tomography (MDCT) and detection of in-stent restenosis at low exposure settings.

Patients/methods

Sixteen patients with 19 renal artery stents underwent CT angiography. A biphasic protocol was performed including arteriographic acquisition at standard 120 kVp and a late-arterial scan at 100 kVp (n = 9) or 80 kVp (n = 7). Images were reconstructed under various algorithms. Signal-to-noise and contrast-to-noise ratios (SNR, CNR) were determined within stent, aorta and renal arteries. Image quality and the presence of restenosis were assessed. Volume CT dose-index was recorded and dose reduction (DR%) between phases was calculated.

Results

Ten patients presented with Hounsfield values >250 HU in all segments, phases and reconstructions and were further evaluated. The 120 kVp protocol performed better in all vessels and reconstruction algorithms. SNR at 120 kVp (B31f) did not differ significantly compared to 100 kVp (B31f). CNR within stent was borderline compromised at 100 kVp (p = 0.042). All but two image sets (at 80 kVp) were considered diagnostic. Minor loss of subjective image quality was noticed at 100 kVp. No difference in assessment of restenosis was observed between 120 kVp and the diagnostic low-exposure scans. Mean DR% was estimated 45% at 100 kVp and 77% at 80 kVp.

Conclusions

Renal MDCT angiography and stent-restenosis assessment are feasible at 100 kVp with minor loss of image quality and almost half radiation exposure.     

Calcium score of small coronary calcifications on multidetector computed tomography: Results from a static phantom study

Introduction

Multi detector computed tomography (MDCT) underestimates the coronary calcium score as compared to electron beam tomography (EBT). Therefore clinical risk stratification based on MDCT calcium scoring may be inaccurate. The aim of this study was to assess the feasibility of a new phantom which enables establishment of a calcium scoring protocol for MDCT that yields a calcium score comparable to the EBT values and to the physical mass.

Materials and methods

A phantom containing 100 small calcifications ranging from 0.5 to 2.0 mm was scanned on EBT using a standard coronary calcium protocol. In addition, the phantom was scanned on a 320-row MDCT scanner using different scanning, reconstruction and scoring parameters (tube voltage 80–135 kV, slice thickness 0.5–3.0 mm, reconstruction kernel FC11–FC15 and threshold 110–150 HU). The Agatston and mass score of both modalities was compared and the influence of the parameters was assessed.

Results

On EBT the Agatston and mass scores were between 0 and 20, and 0 and 3 mg, respectively. On MDCT the Agatston and mass scores were between 0 and 20, and 0 and 4 mg, respectively. All parameters showed an influence on the calcium score. The Agatston score on MDCT differed 52% between the 80 and 135 kV, 65% between 0.5 and 3.0 mm and 48% between FC11 and FC15. More calcifications were detected with a lower tube voltage, a smaller slice thickness, a sharper kernel and a lower threshold. Based on these observations an acquisition protocol with a tube voltage of 100 kV and two reconstructions protocols were defined with a FC12 reconstruction kernel; one with a slice thickness of 3.0 mm and a one with a slice thickness of 0.5 mm. This protocol yielded an Agatston score as close to the EBT as possible, but also a mass score as close to the physical phantom value as possible, respectively.

Conclusion

With the new phantom one acquisition protocol and two reconstruction protocols can be defined which produces Agatston scores comparable to EBT values and to the physical mass.     

Diagnostic accuracy of 64-slice multidetector CT for detection of in-stent restenosis in an unselected, consecutive patient population

Objectives

To investigate the diagnostic accuracy of 64-slice multidetector computed tomography (64-CT) for detection of in-stent restenosis (ISR) in an unselected, consecutive patient population.

Background

Detection of in-stent restenosis by cardiac CT would be a major advance for the evaluation of patients suspected of having ISR. However, the diagnostic accuracy of current generation 64-CT in this context is not fully established.

Methods

We conducted a prospective study on patients with stable angina or acute coronary syndrome with no prior history of coronary artery disease. Six months after percutaneous coronary intervention (PCI) with stent placement they underwent a 64-CT scan (Toshiba Multi-Slice Aquilion 64) and consequently a repeat coronary angiography for comparison. Cardiac CT data sets were analyzed for the presence of in-stent restenosis by two independent expert readers blinded to the coronary angiographic data.

Results

Ninety-three patients with a total of 140 stents were evaluated. Males comprised 82% of the study group and the mean age was 63 ± 10 years. The mean time from PCI to the repeat coronary angiography was 208 ± 37 days and the mean time from 64-CT to repeat coronary angiography was 3.7 ± 4.9 days. The restenosis rate according to coronary angiography was 26%. Stent diameter, strut thickness, heart rate and body mass index (BMI) significantly affected image quality. The sensitivity, specificity, positive and negative predictive values of 64-CT for detection of in-stent restenosis were 27%, 95%, 67% and 78%, respectively.

Conclusions

Current generation, 64-slice CT, remains limited in its ability to accurately detect in-stent restenosis.     

Noninvasive evaluation of coronary artery stents patency after PTCA: role of Multislice Computed Tomography

PURPOSE: Restenosis of a coronary artery treated with stent implantation is a well-known process that can compromise over time the success of a coronary angioplasty and, accordingly, treated patients must undergo periodic controls. We have recently witnessed a shift towards a greater use of Multi-slice CT (msCT) in the study of coronary disease without its precise indications and limits having yet been underlined. The purpose of our study is to assess the role of msCT in the follow-up of patients treated with coronary angioplasty. MATERIALS AND METHODS: Forty-eight patients, for a total of 72 lesions, who underwent treatment with a slotted tube stent implant, had an msCT examination 1 week before scheduled coronary angiography, and the results were compared. 34 stents/72 (47.2%) were inserted on the left anterior descending; 21/72 (29.2%) on the right coronary; 17/72 (23.6%) on the circumflex artery or obtuse marginal branches. RESULTS: The observation of the opacification of the vessel located distally to treated segments allowed us to assess the patency of all stents. Coronary angiography identified a significant intrastent restenosis or a stent occlusion in 12 of the 72 stents analysed (16.7%). msCT enabled easier visualization of the lumen of the treated artery and its differentiation from the stent struts in the ones located on the left anterior descending artery than those on the circumflex (28 stents out of 34 [82.4%] vs 13/17 [76.5%]; p<0.05), and on the right coronary artery, which were difficult to evaluate (11/21 [52.4%]). We were also able to visualize the lumen of 14/15 stents with a calibre over 3.5 mm [93.3%] vs 35/45 stent with dimensions between 3.1 e 3.4 mm [77.8%], and only 4 stents <3 mm/12 [33.3%]. On multivariate analysis, the characteristics that were significantly and independently associated with accurate visualization of the lumen of a stented vessel were location on the proximal anterior descending artery (OR 4.03 [IC 95%: from 2.34 to 8.05]; p<0.0001) and stent size of >3.5 mm (OR 2.97 [IC 95%: from 1.67 to 4.86]; p<0.01). CONCLUSIONS: The msCT technology available at present makes the study of smaller stents and those positioned on the right coronary artery and circumflex rather complex; on the other hand msCT appears a promising study method for stents greater then 3.5 mm and for those positioned on the proximal segment of the left anterior descending artery.