CT Acquisition and Reconstruction Techniques for Transcatheter Aortic Valve Procedure

CT Acquisition and Reconstruction Techniques for Transcatheter Aortic Valve Procedure Planning Utilizing Siemens Healthineers Hardware WRITTEN IN COLLABORATION WITH: SIEMENS Healthineers EDITED BY: Philipp Blanke, MD, FSCCT Radiologist, Center for Heart Valve Innovation, St. Paul’s Hospital Assistant Professor, University of British Columbia, Vancouver, BC Erin Fletcher RN, BSN, RCIS Sr. Global Product Training Manager Imaging, Procedure, and Patient Initiatives Edwards Lifesciences Ricarda Grund Marketing Manager Computed Tomography Siemens Healthineers Astrid Hamann Clinical Marketing Manager Cardiovascular Computed Tomography Siemens Healthineers Edwards For additional support please contact your local applications specialist. This paper is provided as an educational resource to medical personnel by Edwards Lifesciences and Siemens Healthineers. The information in this white paper has been compiled from available literature. Although every effort has been made to faithfully report the information, the editors and publisher cannot be held responsible for the correctness. This paper is not intended to be, and should not be construed as, medical advice. For any use, the product information guides, inserts, and operation manuals of the various drugs and devices should be consulted. Edwards Lifesciences, Siemens Healthineers and the editors disclaim any liability arising directly or indirectly from the use of drugs, devices, techniques, or procedures described in the reference guide. WARNING: Any reference to X-ray exposure, intravenous contrast dosage, and other medication is intended as a reference guideline only. The guidelines in this document do not substitute for the judgment of a health care provider. Each scan requires medical judgment by the health care provider about exposing the patient to ionizing radiation. Use the As Low As Reasonably Achievable (ALARA) radiation dose principle to balance factors such as the patient’s condition, size, and age; region to be imaged; and diagnostic task. NOTE: Algorithms/protocols included in this book are for educational reference only. Edwards does not endorse or support any one specific algorithm/ protocol. It is up to each individual clinician and institution to select the treatment that is most appropriate. Philipp Blanke, MD is a paid consultant to Edwards Lifesciences. INTRODUCTION Transcatheter aortic valve procedures have proven to be an effective alternative in the treatment of aortic stenosis. Contrast- enhanced computed tomography (CT) has become an integral part of transcatheter aortic valve procedure planning by allowing for anatomical assessment of the aortic root and the aorto-iliofemoral vasculature within a single examination. It is critical that artifact-free image data is obtained to allow for reliable anatomical measurements. Data acquisition strategies and scanning protocols may vary depending on scanner manufacturer, system, and institutional preferences. This document provides recommendations for reliable CT image acquisition for transcatheter aortic valve procedures. I 3 WORK-FLOW RATIONALE The key component of all approaches is an ECG-assisted data acquisition that covers at least the aortic root, while the remainder of the data acquisition may be performed without ECG assistance. If employed properly, ECG assistance allows for artifact-free depiction of the aortic root. The sequence of patient preparation and the relevant principles of CT data acquisition will be explained in brief below. PATIENT PREPARATION • Position the patient, typically supine, on the scanner table to closely resemble cath lab table positioning. This is important for the prediction of C-arm angulation from the CT dataset. • Place ECG-electrodes and IV access in accordance with institutional policies. • Provide time for the patient to practice the breath hold prior to scan acquisition to improve patient compliance and thereby scan quality. • Allow additional scanning and instruction time as needed due to the advanced age and frailty of this patient population. CT SCAN – SCAN LENGTH AND SCAN STRATEGY In general, two different approaches are used to combine the ECG-assisted data acquisition of the aortic root structures and the non-ECG-assisted computed tomography angiography (CTA) of the aorto/ilio/femoral vasculature for evaluation of the transfemoral access route: 1) Cardiac ECG-assisted data acquisition of the heart and aortic root (usually beginning 2cm below the carina) followed by a non-ECG-assisted CTA of the thorax, abdomen, and pelvis. Although this approach results in repeat data acquisition of the aortic root and cardiac structures, the time-intensive ECG-assisted data acquisition is kept to a minimum that aids in limiting the contrast dose. Furthermore, by limiting the ECG- assisted data acquisition this decreased the radiation dose-intensive portion of the examination, although the cardiac scan range is covered twice. The proposed protocols for all Siemens Healthineers scanners use this approach. 2) ECG-assisted data acquisition of the thorax followed by a non-ECG-assisted CTA of the abdomen and pelvis. The disadvantage of this approach is the relatively long acquisition time required for the entire thorax (may exceed 15 seconds), which increases the risk of breathing artifacts at the level of the cardiac structures. 4 I Edwards Lifesciences SOMATOM Definition Flash, SOMATOM Drive, and SOMATOM Force SOMATOM Definition Flash, SOMATOM Drive, and SOMATOM Force are Dual Source CT systems allowing for a heart rate independent temporal resolution of 75 ms and 66 ms, respectively, when rotation times of 0.28 s and 0.25 s are employed. 1. Topogram General Data acquisition • AP topogram covering the thorax, • Manufacturers’ default setting abdomen, and pelvis including the proximal femoral to the lesser trochanter 2. CaSc (optional) General Data acquisition Data reconstruction • Can be used for visualization of Axial reconstruction within the ECG • Prospective ECG-triggering • annular calcification CARE kV: Off trigger window, commonly BestDiast • • Can be used for planning of Ref. kVp: 120 kVp • Field of view limited to the heart • subsequent contrast-enhanced data • Slice thickness: 3 mm • CARE Dose4D™: On acquisition • Ref. mAs: 80 mAs/rot • Increment: 1.5 mm WFBP Reconstruction (filtered • Default trigger in end-systole • • Slice/Collimation: back projection) 2 x 128 x 0.6 mm (SOMATOM • Convolution kernel: Definition Flash, SOMATOM Drive) B35f (SOMATOM Definition Flash, 2 x 192 x 0.6 mm (SOMATOM SOMATOM Drive) Force) Qr36 (SOMATOM Force) • Scan direction cranio-caudal • Rotation time: 0.28 s (SOMATOM Definition Flash, SOMATOM Drive) 0.25 s (SOMATOM Force) • Temporal resolution 75 ms (SOMATOM Definition Flash, SOMATOM Drive) 66 ms (SOMATOM Force) 3. Premonitoring for Bolus tracking (CARE Bolus) General Data acquisition • Plan location of pre-monitoring on (manufacturers’ default settings) topogram: 2 cm below carina • Delay: 2 s • Alternatively plan pre-monitoring • Effective (eff.) mAs: 24 mAs using the CaSc CT data • Effective (eff.) kVp: 120 kVp Pre-monitoring should transect • Slice/Collimation: • through ascending aorta Acq. 1 x 10.0 mm • Place region of interest (ROI) within the ascending aorta 4. Monitoring for Bolus tracking (CARE Bolus) General Data acquisition • Same location as pre-monitoring (manufacturers’ default settings) • Threshold: CARE Bolus (automatic • Delay: 10 s bolus tracking) monitors the attenuation • Effective (eff.) mAs: 24 mAs within the vessel of interest (ascending • Effective (eff.) kVp: 120 kVp aorta). The full dose of contrast media Slice/Collimation: • is injected at the decided flow rate. The Acq. 1 x 10.0 mm CTA acquisition (#5) is automatically triggered when the vessel enhancement reaches the pre-defined HU level (100 HU) above the baseline. I 5 SOMATOM Definition Flash, SOMATOM Drive, and SOMATOM Force (CONT) 5. Retrospective ECG-gated spiral data acquisition – Contrast enhanced General Data acquisition Data reconstruction • ECG-gated Dual Source data • Delay after monitoring has reached • Axial multiphasic reconstruction acquisition of the aortic root and threshold: 6 s covering the entire cardiac cycle, heart • Breath hold command: Inspiration only 5 or 10% intervals in sinus rhythm, Plan data acquisition on topogram: 50 ms intervals in atrial fibrillation • • CARE kV: On (Dose saving optimized Scan range beginning 2 cm below for “vasculature”) • Use ECG editing if necessary the carina to the apex of the heart • Ref. kVp: 100 kVp • Field of view limited to the heart • Use unenhanced CaSc CT data for Slice thickness: 0.75 mm • Reference tube current: • planning if available Flash: 376 mAs/rot • Increment: 0.5 mm Drive: 281 mAs/rot • Medium smooth convolution kernel Force: 281 mAs/rot with either filtered back projection B26f (SOMATOM Definition Flash, • Anatomical dose modulation: CARE Dose4D™ on SOMATOM Drive) Bv40 Pulsing (dose modulation throughout (SOMATOM Force) or iterative • cardiac cycle): Off reconstruction (e.g SAFIRE/ Slice/Collimation: ADMIRE, strength 3) • 2 x 128 x 0.6 mm (SOMATOM Definition Flash, SOMATOM Drive) 2 x 192 x 0.6 mm (SOMATOM Force) • Scan direction: Cranio-caudal Pitch: automatic (adaption to heart rate) • • Rotation time: 0.28 s (SOMATOM Definition Flash, SOMATOM Drive) 0.25 s (SOMATOM Force) • Temporal resolution 75 ms (SOMATOM Definition Flash, SOMATOM Drive) 66 ms (SOMATOM Force) 6. High-pitch CTA of the thorax, abdomen, pelvis – Contrast enhanced General Data acquisition Data reconstruction • High-pitch (“Flash”) Dual Source • Delay 5 s (minimum delay; needed • Axial reconstructions data acquisition of the thorax, for repositioning the patient table and • Slice thickness: 0.75 mm abdomen, and pelvis adjusting the tube-detector system) • Increment: 0.5 mm • Scan range: Upper thoracic • No additional automated breath hold • Medium smooth convolution aperture to the proximal femoral command; alternatively manual kernel with either filtered back (lesser trochanter) instruction to slowly exhale. CARE kV: On (Dose saving optimized projection B26f (SOMATOM • for “vasculature”) Definition Flash, SOMATOM Drive) Bv40 (SOMATOM Force) or iterative • Ref. kVp: 100 kVp reconstruction (e.g SAFIRE/ • Reference tube current: ADMIRE, strength 3) Flash: 376 mAs/rot Drive: 281 mAs/rot Force: 281 mAs/rot • Anatomical dose modulation: CARE Dose4D™ on • Slice/Collimation: 2 x 128 x 0.6 mm (SOMATOM Definition Flash, SOMATOM Drive) 2 x 192 x 0.6 mm (SOMATOM Force) • Pitch: 3.4 (SOMATOM Definition Flash, SOMATOM Drive) 3.2 (SOMATOM Force) • Rotation time: 0.28 s (SOMATOM Definition Flash, SOMATOM Drive) 0.25 s (SOMATOM Force) • Temporal resolution 75 ms (SOMATOM Definition Flash, SOMATOM Drive) 66 ms (SOMATOM Force) 6 I Edwards Lifesciences Contrast application protocol General Specific • Single contrast application for both the retrospectively • Contrast bolus monitoring and timing of data acquisition ECG-gated CTA of the aortic root/heart and the CTA of the by means of bolus tracking at the level of the ascending aorta thorax/abdomen/pelvis with an ROI placed within the ascending aorta; threshold • Placement of an IV access in an antecubital vein (an set at 100 HU above baseline, delay to start of data 18-guage IV typically provides the highest safety) acquisition after reaching threshold 6 s • Automated contrast injection using a dual-cylinder injector • The proposed delay can be considered a default setting and may be increased in patients with poor ejection fraction. This may help prevent the high-pitch spiral acquisition from outrunning the bolus. I 7 SOMATOM Definition AS64, AS+, and SOMATOM Definition Edge SOMATOM Definition AS64, AS+, and SOMATOM Definition Edge are single source CT systems for a heart rate independent temporal resolution of 150 ms and 142 ms, respectively, when rotation times of 0.3 s and 0.28 s are employed. 1. Topogram General Data acquisition • AP topogram view covering the • Manufacturers’ default setting thorax, abdomen, and pelvis including the proximal femoral to the lesser trochanter 2. CaSc (optional) General Data acquisition Data reconstruction • Can be used for visualization of • Prospective ECG-triggering • Axial reconstruction within the ECG annular calcification • CARE kV: Off trigger window, commonly BestDiast • Can be used for planning of • Ref. kVp: 120 kVp • Field of view limited to the heart subsequent contrast-enhanced data • CARE Dose4D™: On • Slice thickness: 0.75 mm acquisition Ref. mAs: 80 mAs/rot Increment: 0.5 mm • • • Default trigger in end-systole • Convolution kernel: B35f Heart View Slice/Collimation: medium CaSc 64 x 0.6 mm (SOMATOM Definition AS) 128 x 0.6 mm (SOMATOM AS+ & Edge) • Scan direction: Cranio-caudal • Rotation time: 0.3 s (SOMATOM Definition AS & AS+) 0.28 s (SOMATOM Definition Edge) • Temporal resolution 150 ms (SOMATOM Definition AS & AS+) 142 ms (SOMATOM Definition Edge) 3. Pre-monitoring for Bolus tracking (CARE Bolus) General Data acquisition • Plan location of pre-monitoring (manufacturers’ default settings) on topogram: 2 cm below carina • Delay: 2 s • Alternatively plan pre-monitoring • Effective (eff.) mAs: 40 mAs using the CaSc CT data. Pre- • Effective (eff.) kVp: 120 kVp monitoring should transect through • Slice/Collimation: ascending aorta. Acq. 1 x 10.0 mm • Place ROI within the ascending aorta 4. Monitoring for Bolus tracking (CARE Bolus) General Data acquisition (manufacturers’ • Same location as pre-monitoring default settings) • Threshold: CARE Bolus (automatic • Delay: 10 s bolus tracking) monitors the attenuation • Effective (eff.) mAs: 40 mAs within the vessel of interest (ascending • Effective (eff.) kVp: 120 kVp aorta). The full dose of contrast media • Slice/Collimation: is injected at the decided flow rate. Acq. 1 x 10.0 mm The CTA acquisition (#5) is automatically triggered when the vessel enhancement reaches the pre-defined HU level (100 HU) above the baseline. 8 I Edwards Lifesciences 5. Retrospective ECG-gated spiral data acquisition – Contrast enhanced General Data acquisition Data reconstruction • ECG-gated data acquisition of the • Delay after monitoring has reached • Axial multiphasic reconstruction aortic root and heart threshold: 7 s covering the entire cardiac cycle, • Plan data acquisition on topogram: • Breath hold command: Inspiration 5 or 10% intervals in sinus rhythm, Scan range beginning 2 cm below only 50 ms intervals in atrial fibrillation the carina to the apex of the heart Use ECG editing if necessary • CARE kV: On (Dose saving • • Use unenhanced CaSc CT data for optimized for “vasculature”) • Field of view limited to the heart planning if available • Ref. kVp: 100 kVp • Slice thickness: 0.75 mm • Reference tube current:188 mAs/rot • Increment: 0.5 mm • Anatomical dose modulation: CARE • Medium smooth convolution kernel Dose4D™ on with either filtered back projection • Pulsing (dose modulation throughout (B26f) or iterative reconstruction cardiac cycle): Off (e.g SAFIRE, strength 3) • Slice/Collimation: 64 x 0.6 mm (SOMATOM Definition AS) 128 x 0.6 mm (SOMATOM Definiton AS+ & Edge) • Scan direction: Cranio-caudal • Pitch: Automatic (adaption to heart rate) • Rotation time: 0.3 s (SOMATOM Definition AS & AS+) 0.28 s (SOMATOM Definition Edge) • Temporal resolution 150 ms (SOMATOM Definition AS & AS+) 142 ms (SOMATOM Definition Edge) 6. CTA of the thorax/abdomen/pelvis – Contrast enhanced General Data acquisition Data reconstruction • Scan range: Upper thoracic (manufacturers’ default settings) • Axial reconstructions aperture to the proximal • Delay 5s (minimum delay; needed • Slice thickness: 0.75 mm femoral (lesser trochanter) for repositioning of the patient table • Increment: 0.5 mm and adjusting the tube-detector • Medium smooth convolution kernel system) with either filtered back projection • No additional automated breath (B26f) or iterative reconstruction hold command; alternatively manual (e.g SAFIRE, strength 3) instruction to slowly exhale. • CARE kV: On (Dose saving optimized for “vasculature”) • Ref. kVp: 100 kVp • Effective mAs: 100 mAs • Anatomical dose modulation: CARE Dose4D™ on • Slice/Collimation: 64 x 0.6 mm (SOMATOM Definition AS) 128 x 0.6 mm (SOMATOM AS+ & Edge) • Scan direction: Cranio-caudal • Pitch: 1.5 • Rotation time: 0.3 s (SOMATOM Definition AS & AS+) 0.28 s (SOMATOM Definition Edge) • Temporal resolution 150 ms (SOMATOM Definition AS & AS+) 142 ms (SOMATOM Definition Edge) I 9 Contrast application protocol General Specific • Single contrast application for both the retrospectively • Contrast bolus monitoring and timing of data acquisition ECG-gated CTA of the aortic root/heart and the CTA of by means of bolus tracking at the level of the ascending the thorax/abdomen/pelvis aorta with a ROI placed within the ascending aorta; • Placement of IV access in an antecubital vein (an threshold set at 100 HU above baseline, delay to start of 18-guage IV typically provides the highest safety) data acquisition after reaching threshold 7 s • Automated contrast injection using a dual-cylinder injector LOW-CONTRAST DOSE PROTOCOL – RATIONALE FOR ALL SCANNER TYPES Same scanner settings as listed above, except the threshold setting for bolus tracking • • Reduce scan length of the retrospectively ECG-gated CTA (#5) to a minimum to cover only the aortic root as opposed to the entire heart, as this is the time-intensive part in regard to data acquisition Injection rate might be lowered • Threshold to trigger initiation of the retrospective ECG-gated spiral data acquisition can • be lowered to 80 HU • Systems with the capability of low kV data acquisition (70 kV - 90 kV, SOMATOM Force) may allow for reduced iodine delivery rates as low kV data acquisition increases iodine attenuation; CARE kV settings need to be adjusted (setting 4-7) These alterations should allow for a sufficiently contrast-enhanced CT dataset of the aortic root. Contrast attenuation of the iliofemoral acquisition may be variable. DOSE MODULATION FOR RETROSPECTIVE ECG-GATED SPIRAL DATA ACQUISITION The protocols listed above do not employ dose modulation for the retrospective ECG-gated spiral data acquisition, allowing for image reconstructions throughout the entire cardiac cycle at a constant image noise level. This allows for identifying the reconstruction phase with largest annular dimensions and optimal image quality. If dose modulation is employed, peak dose should be applied during systole with a pulsing window set to 5 –35%. Outside of peak pulsing, there are two pulsing options, Auto Dose Pulsing and MinDOSE Auto. The operator should be mindful of the effect of these two options as image noise will increase as a result of dose reduction in this application with MinDOSE having the greatest impact on noise. 10 I Edwards Lifesciences RECONSTRUCTION OF MULTIPHASIC DATA SET Multiphasic (“dynamic”, “cine”) data sets can be reconstructed using a relative approach (percentage intervals [%] between two R-peaks) or an absolute approach (fixed distance of the reconstruction window from the R-peak, reported as [ms]). The relative approach (e.g. 5 or 10% intervals) performs well in regular sinus rhythm. In case of increased heart rate variability, atrial fibrillation, or ectopic beats, absolute reconstruction should be employed (e.g. 50 ms) in combination with ECG-editing if necessary. CAVEAT: “BestDiastole” and “BestSystole” are algorithms which aim at automated identification of optimal reconstruction phases with the least coronary artery motion in diastole or systole. However, these algorithms are intended for coronary CTA and not aortic root imaging. REVIEW OF DATA RECONSTRUCTION AND ECG-EDITING Image reconstructions of the aortic root and heart should be reviewed immediately • after the scan when raw data is still available The ECG-gating should be reviewed to ensure that the automated algorithms • correctly identified the R-peaks (dots, also known as “Syncs” should be aligned with R-peaks) If R-peaks were not correctly identified, manual correction should be performed (e.g. “Insert • Sync” if an R-peak was not identified, or “Delete Sync” if a Sync was placed on anything other than the R-peak; alternatively Syncs can also be shifted manually) In case of ectopic contractions, absolute reconstruction should be used and the Sync of • the ectopic beat should be deleted 49 49 Disable Sync 8 9 10 11 • If mis-registration or stair-step artifacts are present, ECG-editing should be employed with either modification of trigger-points (if they were initially incorrectly identified by the algorithm) or deletion of trigger-points (in premature contraction or atrial fibrillation) I 11 Written in collaboration with SIEMENS Healthineers References 1. 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Multidetector Computed Tomography in Transcatheter Aortic Valve Implantation. JACC Cardiovasc Imaging 2011;4(4):416-429. 7. Litmanovich DE, Ghersin E, Burke DA, et al. Imaging in Transcatheter Aortic Valve Replacement (TAVR): role of the radiologist. Insights Imaging 2014; 5:123-145. Edwards, Edwards Lifesciences, and the stylized E logo are trademarks of Edwards Lifesciences Corporation. All other trademarks are the property of their respective owners. © 2016 Edwards Lifesciences Corporation. All rights reserved. PP--ALL-0018 v4.0 E5665/6-15/THV © Siemens Healthcare GmbH, 2016 Edwards Lifesciences I edwards.com One Edwards Way I Irvine, California 92614 USA Switzerland I Japan I China I Brazil I Australia I India Edwards