Rationale and Objectives
To investigate the diagnostic performance of a comprehensive computed tomography (CT) protocol for both cardiac and aortoiliac evaluation of patients considered for transcatheter aortic valve replacement (TAVR) using a single, low-volume contrast medium (CM) injection.
Materials and Methods
Forty-four TAVR candidates were retrospectively analyzed. All underwent retrospectively electrocardiogram-gated cardiac CT followed by high-pitch CT angiography of the aortoiliac vasculature using one of two single injection protocols of 320 mgI/mL iodine CM: group A ( n = 22), iodine delivery rate-based (1.28 gI/s), 60-mL CM volume, 4.0 mL/s flow rate; group B ( n = 22), clinical routine protocol, 100-mL CM volume, 4.0 mL/s flow rate. Mean arterial attenuation, signal-to-noise ratio (SNR), and contrast-to-noise ratio (CNR) were calculated. Subjective image quality was assessed.
Results
Aortic root and iliofemoral dimensions could be analyzed in all cases. Patient characteristics showed no significant differences. Mean attenuation at the levels of the aortic root (285.8 ± 83.0 HU vs 327.5 ± 70.8 HU, P = .080) and the iliofemoral access route (256.8 ± 88.5 HU vs 307.5 ± 93.2 HU, P = .071), as well as SNR and CNR were nonsignificantly lower in group A compared to group B. Subjective image quality was equivalent.
Conclusions
In multimorbid TAVR patients, the performance of a combined CT protocol using a single low-volume CM bolus is feasible with maintained image quality compared to a standard protocol.
Transcatheter aortic valve replacement (TAVR) is an emerging minimally invasive procedure for patients with severe aortic valve stenosis who are considered at high risk for surgical treatment . A comprehensive preprocedural diagnostic work-up is essential for patient selection and proper TAVR planning . In this context, computed tomography (CT) is increasingly gaining importance as it provides information on both aortic annular sizing for prosthesis deployment and the aortoiliac access route within a single examination . Compared to other imaging modalities, CT offers this information noninvasively with three-dimensional reconstructions possible and without interference by overlaying structures. However, CT protocols of multiple body regions typically require a considerable amount of contrast medium (CM) using a conventional single-source CT system .
While designing an optimal CT protocol for TAVR planning, it is important to consider three frequent comorbid conditions in patients considered for TAVR: atrial fibrillation, heart failure, and chronic renal dysfunction , as they have both technical and clinical implications. Atrial fibrillation is important in that it might lead to incorrect aortic root measurements caused by cardiac motion and electrocardiogram (ECG) misregistration. This can be ameliorated by using a retrospectively ECG-gated image acquisition mode, which can also account for the conformational changes of the aortic annulus over the cardiac cycle that influence prosthesis sizing . Congestive heart failure and renal insufficiency together increase the risk of volume overload and renal compromise. Therefore, minimizing CM volume is desirable .
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Materials and methods
Patients
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CM Injection Protocol
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Table 1
CT Protocol for Combined Assessment of the Aortic Root Complex and the Aortoiliac access Route in TAVR Candidates
Parameter Heart Aortoiliac Vasculature CT protocol Tube voltage (kV) Adaptive Adaptive Tube current (modulated), mAs ref 500 500 Collimation 2 × 64 × 0.6 2 × 64 × 0.6 Rotation time (ms) 280 280 Pitch Heart rate adaptive 3.2 Study range Tracheal bifurcation to bottom of heart Lung apices to femoral heads Acquisition direction Caudocranial Craniocaudal ECG synchronization Retrospective Prospective Target R-R interval for data acquisition 0%–100% 35% Injection protocol Bolus timing Bolus tracking: threshold 100 HU, ROI in descending aorta (at the level of the bottom of the heart) Delay (s) 2 s (after threshold) 4 s (delay after cardiac study) Total CM volume (mL) 60 Flow rate (mL/s) 4.0 Image reconstruction (basic reconstructions) Aortic root complex Aortoiliac access route Section thickness (mm) 0.75 1.5 Increment (mm) 0.4 0.7 Kernel B26f B30f Reconstruction window 300 ms (absolute forward) 35% (single heart beat) Multiplanar reformation Sagittal, coronal: 2 mm
CM, contrast medium; CT, computed tomography; ECG, electrocardiogram; ROI, region of interest; TAVR, transcatheter aortic valve replacement.
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CT Protocol
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Image Reconstruction
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Qualitative Image Assessment
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Quantitative Assessment of IQ
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SNR=HUvessel/noise SNR
=
HU
vessel
/
noise
CNR=(HUvessel−HUmuscle)/noise CNR
=
(
HU
vessel
−
HU
muscle
)
/
noise
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Radiation Dose
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Statistical Analysis
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Results
Demographics
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Qualitative Image Assessment
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Quantitative Assessment of IQ
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Table 2
Assessment of Objective Image Parameters
Parameter Attenuation (HU) SNR CNR Group A Group B_P_ Value Group A Group B_P_ Value Group A Group B_P_ Value Summary scores Cardiac 285.8 ± 83.0 327.5 ± 70.8 .080 16.3 ± 7.2 16.9 ± 5.3 .760 13.8 ± 6.6 14.4 ± 4.9 .664 Access route234.2 ± 79.1290.8 ± 95.0.038* 8.4 ± 3.4 11.1 ± 5.8 .069 6.7 ± 3.2 9.4 ± 5.3 .055 Aorta207.1 ± 71.5270.6 ± 105.8.024* 7.9 ± 3.6 11.3 ± 7.4 .0606.1 ± 3.39.4 ± 6.8.043* Iliac arteries 256.8 ± 88.5 307.5 ± 93.2 .071 8.9 ± 3.6 10.9 ± 4.9 .123 6.1 ± 3.3 9.4 ± 6.8 .109 Cardiac levels Pulmonary artery162.8 ± 76.8253.0 ± 128.6.007*9.0 ± 5.014.0 ± 7.9.038*6.4 ± 4.711.3 ± 8.6.030* Left ventricle 311.1 ± 103.1 325.0 ± 75.0 .611 16.6 ± 9.5 16.2 ± 9.8 .703 14.9 ± 8.1 14.1 ± 7.9 .739 Aortic root 317.8 ± 106.5 340.9 ± 72.7 .407 15.7 ± 9.6 15.3 ± 6.0 .461 15.3 ± 9.2 13.7 ± 5.6 .492 Ascending aorta 315.3 ± 104.6 367.9 ± 71.9 .058 17.5 ± 9.6 21.8 ± 10.9 .550 15.6 ± 8.3 17.0 ± 6.2 .536 Descending aorta 322.1 ± 101.3 350.9 ± 74.7 .289 15.3 ± 7.4 17.7 ± 7.0 .928 16.4 ± 9.4 16.1 ± 6.2 .912 Aortoiliac levels Ascending aorta186.0 ± 63.1262.3 ± 114.8.010* 8.0 ± 4.2 12.4 ± 9.7 .0575.8 ± 3.510.2 ± 8.9.035* Aortic arch188.8 ± 64.0262.5 ± 108.7.010*7.8 ± 3.312.2 ± 9.3.042*5.7 ± 2.810.0 ± 8.5.033* Descending aorta (level 1)191.4 ± 69.5259.1 ± 108.1.018*7.8 ± 3.411.8 ± 8.4.045*5.7 ± 2.99.7 ± 7.6.025* Descending aorta (level 2) 221.7 ± 82.5 274.5 ± 107.7 .075 7.3 ± 4.0 9.5 ± 5.1 .104 5.9 ± 3.7 8.0 ± 4.6 .101 Descending aorta (level 3) 247.4 ± 91.7 294.8 ± 104.8 .118 8.8 ± 5.1 10.7 ± 6.1 .255 7.3 ± 4.8 9.2 ± 5.7 .234 Common iliac artery 245.9 ± 89.3 300.3 ± 103.9 .073 8.2 ± 4.0 9.8 ± 5.7 .267 6.6 ± 3.8 8.3 ± 5.3 .219 External iliac artery 244.5 ± 94.6 297.8 ± 97.9 .0918.2 ± 3.310.6 ± 4.6.048* 6.7 ± 3.2 8.9 ± 4.4 .059 Common femoral artery 268.3 ± 96.7 326.1 ± 88.5 .073 10.3 ± 4.1 12.3 ± 5.2 .170 8.6 ± 3.9 10.6 ± 4.8 .131
Mean attenuation was measured by using a region of interest analysis. Based on these values, signal-to-noise (SNR) and contrast-to-noise (CNR) ratios were calculated. Values were provided as mean and standard deviation. Significant differences were indicated by bold letters and asterisks.
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Radiation Dose
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Discussion
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