Wide-Detector CT for TAVR Planning: Impact on Iodine Dose, Radiation Dose, and Image Quality SCBTMR 2015 Annual Course Thursday, October 8 William P. Shuman MD FSCBTMR Department of Radiology University of Washington, Seattle
Disclosures WPS administers research grants from GE Healthcare which support clinical CT research
Wide Detector Technology 16 cm detector with focally aligned detector modules Post patient collimator
Detector Technology 16 cm Wide-Detector
Mitigating Wide Coverage Issues cone beam Focally aligned detector modules designed for cone beam geometry VHD reconstruction reduces Hounsfield unit uniformity variation across 160 mm z-axis coverage
Post-Patient Collimator
Wide Detector Technology Axial step-and-shoot technique with 16 cm slabs No helical artifacts Stitching reconstruction of anatomical structures to control or eliminate step-off artifacts
Wide Detector Technology Faster rotation time (0.28 sec) Better ACTM and auto-kvp Partial model-based iterative reconstruction (ASIR-V)
TAVR Transcutaneous Aortic Valve Replacement Patients with severe calcific AS and AI who are not operative candidates due to co-morbidities Femoral, transapical,or trans axillary approaches Implanted ring/valve overlies native valve, displacing leaflets
TAVR Transcutaneous Aortic Valve Replacement Patients with severe calcific AS and AI who are not operative candidates due to co-morbidities Femoral, transapical, or trans axillary approaches Implanted ring/valve overlies native valve, displacing leaflets
Background Wide-detector CT is faster, enabling scanning of chestabdomen-pelvis as a single acquisition with one bolus of contrast Wide Detector CT also has new radiation dose reduction features
Purpose To compare an older clinical standard TAVR planning protocl on a 4 cm detector CT with a new clinical standard protocol on a 16 cm wide-detector CT for: Iodine dose utilized Radiation dose Subjective and objective image quality
Methods IRB approved retrospective study December 2014 January 2015 Large urban academic medical center
Methods Patients Reviewed 36 consecutive patients scanned for TAVR planning on wide-detector Carefully match for gender, age, and BMI to 36 patients previously scanned for TAVR planning on 4 cm detector
Methods Wide-detector Protocol 1 Continuous scanning of ECG gate chest and non-gated abdomen-pelvis. 2 16 cm slabs in the chest, 3 4 16 cm slabs in the abdomen-pelvis Scan duration: 12 16 seconds
Methods Wide-detector Protocol 1 NI = 30 for chest, 18 for abd/pel, kvp = 80-120 rotation 0.28 or 0.35 sec Contrast: 70-105 cc at 3-5 cc/sec base on Z axis Injection duration 5 sec longer than scan duration Reconstructed with ASIR-V 70%
Methods Standard 4cm Detector Protocol 2 Separate acquisitions of the chest (helical ECG gated) and of the abdomen/pelvis (helical non-gated) 30 second pause between the two acquisitions Scan duration: 47 seconds
Methods Standard 4 cm detector Protocol 2 NI = 50 for chest, 30 for abd/pel, kvp = 100-120 rotation time = 0.35 or 0.5 sec Contrast: 110-150 cc at 4 cc/sec Reconstructed with 70% ASIR
Methods Images reconstructed: Axial 2.5 mm of the chest, abdomen, and pelvis 0.625 mm double oblique of aortic valve 0.625 mm magnified - with measurements of annulus, leaflet length, and coronary ostia distances.
Protocol 1 Protocol 2 A B C D
Methods Image Evaluation by 2 independent Reviewers (subjective 4 point Likert scales): aortic enhancement overall image quality for non-vascular structures image quality of aortic annulus
Methods Objective Measurements: HU vascular attenuation at 8 locations in aorta and iliofemorals Psoas HU and Image Noise in air Calculated SNR, CNR
Results Demographics No difference in age, gender, or BMI
Results Wide detector scanner acquisition time averaged 32 seconds less than 4 cm detector scanner
Results Wide detector scanner iodine dose averaged 33% less than standard 4 cm detector scanner
Results Wide detector scanner radiation dose in SSDE was 28 45% lower than standard 4cm detector scanner 53% reduction in total exam DLP with no statistical difference in scan range (mm)
Results Wide detector scanner mean vascular HU attenuation was statistically greater overall and was greater at each of the 8 measurement levels than standard 4cm detector scanner
Results Image noise, SNR, and CNR were the same for both scanners
Results Subjective scores for vascular enhancement and overall image quality were the same Subjective image quality scores for the magnified aortic root measurement images were statistically better for the wide detector scanner
Discussion Wide detector scanner features: Axial step-and-shoot technique No helical artifacts Whole heart in one beat Effective Stitching = no step-off artifacts
Discussion Wide detector scanner features: Focally aligned detector modules Less cone beam artifact Better dose efficiency
Discussion Wide detector scanner features: Three dimensional post-patient collimator Eliminates scatter radiation Less image noise
Discussion Wide detector scanner features: Faster rotation time 0.28 sec Better temporal resolution
Discussion Wide detector scanner features: Faster overall scan acquisition time Transition from ECG gated to ungated shortened from 30 secs. down to 5 secs. Enables single contrast bolus technique
Discussion Wide detector scanner features: ASIR-V reconstruction Partial model based iterative recon. 30% lower noise than statistical iterative recon Supports reduced radiation technique Similar reconstruction time
Conclusion Wide detector axial step-and-shoot TAVR planning CT resulted in: Greater vascular attenuation Similar subjective and objective image noise Lower radiation dose Less iodine dose