CT Radiation Dose at Equal Image Contrast-to-noise Ratio using Iodine- and Novel Tantalum-based Contrast Agents: A Large Habitus Phantom Study Paul FitzGerald Jack W. Lambert Peter M. Edic Robert E. Colborn Andrew S. Torres Peter J. Bonitatibus Benjamin M. Yeh RSNA 2015 PH277-SD-THA6

This work was supported by NIH grant R01EB015476. Disclosures Employees, GE Global Research Paul FitzGerald Peter M. Edic Robert E. Colborn Andrew S. Torres Peter J. Bonitatibus Employees, UCSF Medical Center Benjamin M. Yeh Jack W. Lambert Thank you to my colleagues, and to the NIH for supporting our work. This work was supported by NIH grant R01EB015476. The content is solely the responsibility of the authors and does not necessarily represent the official views of the NIH.

Purpose Quantitatively compare CT imaging performance of iodine- and tantalum-based contrast agents in phantoms representing small, medium-large, and extra-large patients

Methods – key metrics ↑ ↓ C: Image contrast (HU): mean in sample ROI - mean in background ROI N: Image noise (HU): s.d. in background ROI Contrast and noise within valid operating regime DR: Radiation dose (mGy): SSDE w/water-equivalent diameter (DW) CNR (dimensionless): Contrast-to-noise ratio, = C/N DCNR (mGy): Dose normalized by CNR2, = DR/(C/N)2 DVP (mGy-HU2): Dose-variance product, = DR*N2 DVP = DCNR at C = 1, i.e. CNR-normalized dose at low contrast DC: Contrast agent dose (mg element / mL agent)

Methods – phantoms and samples Pseudo-anthropomorphic phantoms model 007TE, CIRS Inc. Thoracic and abdominal versions Modified to accept large sample vial Can be used to measure - Contrast - Noise - Radiation dose

Methods – phantom sizes Label CIRS model 007TE-* AP (cm) LAT (cm) Girth (inch) Water-equivalent diameter, DW (cm) Th. Ab. Adult small S x6 22 30 32 24.3 27.1 Adult Medium-Large ML x7A 28.5 36.5 40 30.8 33.9 Adult Extra-Large XL x9 34 42 47 35.9 39.4   * x = 0 for abdomen x = 1 for thorax

Methods – samples Active Element Atomic number k edge energy (keV) Compound Nominal concentration (mg active element/mL solution) Measured concentration (mg active element/mL solution) Correction factor for active element concentration to be applied to measured HU I 53 33 C35H44I6N6O15  10 9.73 1.03 Ta 73 67 (Ta2O5)(C7H14NO5Si)2.8 10.30 0.97

Results: Initial overview

Results – C (image contrast)

Results – C (image contrast) Image contrast curves are coincident for “ML” and “XL” sizes for both tantalum and iodine

Results – C (image contrast) 54% higher image contrast with tantalum versus iodine in “XL”-sized patients at 140 kVp

Results – DVP (Dose-variance product)

Results – DCNR

Results – First interpretation DVP and DCNR guide us toward the “best” kVp and contrast agent material for each patient size DVP: Small patients: 140 kVp → ~20% lower DR vs. 80 kVp Medium and larger patients: small kVp dependence DCNR: Small patients: iodine @ 80 kVp → slightly lower DR vs. tantalum @ 100 kVp Medium and larger patients: tantalum → much lower DR 50-65% Radiation dose reduction opportunity with tantalum in large, overweight, and obese patients BUT…

Results – DCNR Up to ~65% dose reduction hypothetically possible, assuming that the clinical task is purely angiography and high power is required (e.g. CCTA).

Results – DCNR Otherwise, we can reallocate the higher intrinsic signal of tantalum agent to: reduce radiation dose reduce contrast agent dose improve CNR

Results: Rotation time = 0.5 s CNR and NMax: size-dependent

Results – with size-dependent CNR and NMax Using these CNR and NMax targets,

Results – with size-dependent CNR and NMax With DC constant

Results – with size-dependent CNR and NMax Tantalum can provide: With DC constant DR ↓ ~20%

Results – with size-dependent CNR and NMax Tantalum can provide: CNR ↑ 0 - 30% With DC constant DR ↓ ~20%

Results – size “S”; CNR=15.0; NMax=22.0; ↓DR Prescription 100 kVp 127 mAs D = 9.1 mGy C = 278 HU N = 18.6 HU CNR = 15.0 Iodine Displayed 100 kVp 135 mAs D = 9.6 mGy C = 278 HU N = 18.0 HU CNR = 15.5 Prescription 100 kVp 104mAs D = 7.4 mGy C = 308 HU N = 20.5 HU CNR = 15.0 Tantalum Displayed 100 kVp 110 mAs D = 7.8 mGy C = 308 HU N = 20.0 HU CNR = 15.4 DR ↓ 19% Contrast ↑, Noise ↑, CNR ↔

Results – size “ML”; CNR=12.3; NMax=23.5; ↓DR Prescription 100 kVp 330 mAs D = 18.4 mGy C = 254 HU N = 20.7 HU CNR = 12.3 Iodine Displayed 100 kVp 340 mAs D = 18.9 mGy C = 244 HU N = 20.4 HU CNR = 12.5 Prescription 100 kVp 256mAs D = 14.2 mGy C = 301HU N = 23.5 HU CNR = 12.8 Tantalum Displayed 100 kVp 260 mAs D = 14.5 mGy C = 301 HU N = 23.3 HU CNR = 12.9 Dose ↓ 23% Contrast ↑, Noise ↑, CNR ↑ 4%

Results – size “XL”; CNR=10.1; NMax=24.8; ↓DR Prescription 120 kVp 338 mAs D = 24.7 mGy C = 195 HU N = 22.4 HU CNR = 8.7 Iodine Displayed 120 kVp 340 mAs D = 24.8 mGy C = 195 HU N = 22.0 HU CNR = 8.7 Prescription 120 kVp 276 mAs D = 20.1 mGy C = 279 HU N = 24.8HU CNR = 11.3 Tantalum Displayed 120 kVp 260 mAs D = 19.0 mGy C = 279 HU N = 26.8 HU CNR = 10.9 Dose ↓ 19% Contrast ↑, Noise ↑, CNR ↑ 30%

Conclusion We developed a method to quantitatively compare CT imaging performance of iodine- and tantalum-based contrast agents. In medium-sized and larger adults, Tantalum predicted to provide Up to 65% radiation dose reduction in certain applications - or - Up to 55% higher image contrast and CNR Up to 35% contrast agent dose reduction A combination of the three. Maximum improvement predicted in obese patients. Comparable performance in small adult patients. Iodine predicted to outperform tantalum in smaller patients.