STIR – 1 Digital Phantom Project Kohsuke Kudo, Soren Christensen, Makoto Sasaki, and Leif Ostergaard

Background A variety of post-processing programs and algorithms for CT perfusion and dynamic susceptibility contrast (DSC) MR perfusion are available from CT or MR manufacturers, third-party workstation vendors, and academic groups. However, the accuracy and reliability of these programs have not been subject to standardized quality control.

Purpose To design a digital phantom data set both for CT perfusion and DSC MR perfusion based on widely accepted tracer kinetic theory in which a range of true values of cerebral blood flow (CBF), cerebral blood volume (CBV), mean transit time (MTT), and tracer arrival delay are known. To evaluate the accuracy of post-processing programs using this digital phantom.

Methods – AIF/VOF Arterial input function (AIF) was generated using Gamma-variate function. Venous output function (VOF) was generated by deconvoluting AIF and Exponential R(t).

Methods – AIF/VOF Concentration time curves, C(t), were converted to signal time curves, S(t), for MR.

Methods – Tissue Curves Tissue curves were generated by deconvoluting AIF and R(t). Three kinds of R(t) were used, Exponential, Linear, and Box.

Methods – Tissue Curves Tissue curves were also converted to signal curves for MR.

Methods – Data Structure The phantom data set had 7 slices and 50 phases (total 350 images). Curves for AIF/VOF were embedded in slice #1. Tissue curves were embedded in slice #2 to #7, with different R(t) and CBV. Slice #1 AIF/VOF Slice #2, 3 R(t) = Exp. CBV = 2, 4 % Slice #4, 5 R(t) = Linear Slice #6, 7 R(t) = Box

Methods – AIF/VOF Image -3 -2 -1 Delay (s) = 0 +1 +2 +3 AIFs VOF AIF without delay and VOF were used.

Methods – Tissue Images -3 -2 -1 Delay (s) = 0 +1 +2 +3 MTT (s) = 24 12 8 6 4.8 4 3.4 CBF (mL/100g/min) = 5 10 15 20 25 30 35 (CBV = 2%) 10 20 30 40 50 60 70 (CBV = 4%)

Method – True Values R(t): Exponential, Linear, and Box Delay: -3, -2, -1, +0, +1, +2, and +3 sec CBV: 2 and 4% CBF: 5, 10, 15, 20, 25, 30, and 35 mL/100g/min 10, 20, 30, 40, 50, 60, and 70 mL/100g/min MTT: 3.4, 4, 4.8, 6, 8, 12, and 24 sec

Methods – Evaluation CT Perfusion Commercial Software GE (CTP3, CTP4) Hitachi (IF) Philips (SVD) Siemens (LMS) Toshiba (bMTF, SVD+) Academic Software PMA (sSVD, bSVD) MR Perfusion Commercial Software GE (FM) Hitachi (FM) Philips (FM) Siemens (SVD) Academic Software EPITHET (SVD) Penguin (sSVD, oSVD) Rapid (sSVD, cSVD) PMA (sSVD, bSVD)

Methods - Evaluation Delay Sensitivity Visual Assessment Correlation coefficient with delay Accuracy Correlation coefficient with true value Significant Correlation = Delay Sensitive Higher Correlation = Accurate

Results PMA CBF sSVD Delay MTT/CBF

Results PMA CBF bSVD Delay MTT/CBF

Results – CTP Maps CBF CBV MTT GE CTP3 GE CTP4 Hitachi IF Philips SVD Siemens LLMS Toshiba bMTF Toshiba SVD+ PMA sSVD PMA bSVD

Results – MRP Maps CBF CBV MTT Tmax GE FM Hitachi FM Philips FM Siemens SVD Penguin sSVD Penguin oSVD Rapid sSVD Rapid cSVD PMA sSVD PMA bSVD Tmax EPITHET SVD Penguin sSVD Penguin oSVD Rapid sSVD Rapid cSVD PMA sSVD PMA bSVD

Results – Delay Dependency

Results - Accuracy

Significant correlation Results – CTP Delay Sensitivity Accuracy CBF CBV MTT GE CTP3 -0.177 0.104 0.321 0.940 0.974 0.907 GE CTP4 0.188 0.439 0.337 0.699 0.698 0.888 Hitachi 0.000 0.316 0.404 0.844 0.898 0.885 Philips -0.438 0.011 0.376 0.720 0.867 0.828 Siemens Toshiba bMTF -0.444 0.027 0.455 0.327 0.985 0.851 Toshiba SVD+ PMA sSVD -0.331 0.341 0.958 0.880 PMA bSVD -0.002 0.016 0.942 0.965 Correlation Coefficient to Delay Correlation Coefficient to True Value Significant correlation = Delay sensitive r < 0.9

Significant correlation Results – MRP Significant correlation = Delay sensitive r < 0.9

Summary CT Perfusion Commercial Software GE(CTP3) : accurate but delay sensitive GE(CTP4) : sensitive to negative delay Hitachi(IF) : CBV/MTT are delay sensitive Philips(SVD) : delay sensitive Siemens(LMS) : could not be analyzed Toshiba(bMTF) : delay sensitive Toshiba(SVD+) : could not be analyzed Academic Software PMA(sSVD) : delay sensitive PMA(bSVD) : delay insensitive and accurate

Summary MR Perfusion Commercial Software GE(FM) : delay insensitive but not accurate Hitachi(FM) : delay insensitive but not accurate Philips(FM) : delay insensitive but not accurate Siemens(SVD) : delay sensitive Academic Software EPITHET(SVD) : only Tmax Penguin(sSVD) : delay sensitive Penguin(oSVD) : delay insensitive Rapid(sSVD) : delay sensitive Rapid(cSVD) : delay insensitive and accurate PMA(sSVD) : delay sensitive PMA(bSVD) : delay insensitive and accurate

Newer Version of Phantom All the curves are embedded in “real” brain image, because some programs require anatomical configuration. AIF VOF Only “positive delays” are used, because negative delays are not realistic if we choose proper AIF. Five CBV values are embedded to see linearity of CBV. Noise was added stronger to resemble clinical data.

Preliminary Results for CT CBF CBV MTT GE CTP3 GE CTP4 Hitachi IF Philips SVD Siemens LLMS Toshiba bMTF Toshiba SVD+ PMA sSVD PMA bSVD

Conclusion The digital phantom can be used for the evaluation of accuracy and reliability of perfusion software packages, and also used for the certification and standardized quality control.

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