Ultrasonic Assessment of Perfusion Conditions in the Brain
Ultrasonic Assessment of Perfusion Conditions in the Brain and in Soft Tissue Organs Wilko Wilkening 1, Thomas Postert 2, Saskia Meves 2, Yuko Kono 3, Robert Mattrey 3, Helmut Ermert 1 1 Dept. of Electrical Engineering, 2 Dept. of Neurology Ruhr-University, Bochum, Germany 3 Department of Radiology University of California at San Diego, USA Ultrasonic Assessment of Perfusion Conditions Ruhr-University RF Engineering Institute
Outline • Introduction • Perfusion imaging in the brain – Approach – Experimental results • Perfusion imaging in soft tissue – Approach – Experimental results • Conclusions and outlook Ultrasonic Assessment of Perfusion Conditions Ruhr-University 2/13 RF Engineering Institute
Introduction Perfusion Imaging in the Brain • Almost no motion • Limited volume of interest (stroke) • High attenuation of bone window – destructive imaging mode sensitivity – bolus injection of contrast agent contrast Perfusion Imaging in Soft Tissue • Moderate attenuation • Motion artifacts – nonlinear imaging mode high frame rate • Large volume of interest (tumors) – constant infusion of contrast agent repeatability Ultrasonic Assessment of Perfusion Conditions Ruhr-University 3/13 RF Engineering Institute
Perfusion Imaging in the Brain 2900 Peak Width intensity, [a. u. ] • Bolus injection of contrast agent • Scanning through temporal bone window • Contrast Burst Imaging or Time-Variance Imaging • 0. 5 frames per second • Automated extraction and evaluation of timeintensity curves (TICs) • Model-based analysis 2700 2500 Peak Intensity 2300 2100 0 Time-To-Peak Base Line 20 40 s 60 80 Ultrasonic Assessment of Perfusion Conditions Ruhr-University 4/13 RF Engineering Institute 100
Results: Normal Human Brain Contra-Lateral Scan, TVI, Optison Base Line Image: Tissue Harmonic Imaging Perfusion Image: Peak Intensity from 37 TVI images 0. 3 cm 5. 2 cm -10. 9 cm. . . 10. 9 cm 15. 5 cm Ultrasonic Assessment of Perfusion Conditions Ruhr-University 5/13 RF Engineering Institute
Typical. TICs Artery 50 Parenchyma Peak: 38. 11 [a. u. ], Time: 33. 08 s, Width: 36. 56 s 14 12 Intensity, [a. u. ] 40 30 20 10 0 0 Peak: 8. 44 [a. u. ], Time: 35. 22 s, Width: 11. 51 s 10 8 6 4 20 40 s 60 80 2 0 20 40 s 60 Ultrasonic Assessment of Perfusion Conditions Ruhr-University 6/13 RF Engineering Institute 80
Perfusion Imaging in Soft Tissue: Depletion Approach • Acquisition at a fairly high frame rate, e. g. 5– 10 fps • Short total acquisition time, e. g. 2– 10 s • Constant microbubble concentration in the blood pool during acquisition infusion or bolus (short acquisition time) • Combination of acoustic power and frame rate microbubble concentration decreases during acquisition Ultrasonic Assessment of Perfusion Conditions Ruhr-University 7/13 RF Engineering Institute
Model for Time-Intensity Curve normalized concentration 1 0. 9 0. 8 Destruction 0. 7 Perfusion 0. 6 Measurement 0. 5 Equilibrium 0. 4 0. 3 0. 2 1 2 3 4 5 6 7 insonations 8 9 10 11 Ultrasonic Assessment of Perfusion Conditions Ruhr-University 8/13 RF Engineering Institute
Derivation of an Analytic Model I. Iteration • Concentration in the first frame • Concentration in the nth frame Ultrasonic Assessment of Perfusion Conditions Ruhr-University 9/13 RF Engineering Institute
Derivation of an Analytic Model II. Closed Form Solution • Iteration can be converted into a closed form solution: • Given that enough measurements were taken, all parameters can be estimated • A constant can be added to account for a base line intensity • Mapping intensity to concentration remains an important issue Ultrasonic Assessment of Perfusion Conditions Ruhr-University 10/13 RF Engineering Institute
Results: Rabbit Kidney • Infusion of Imagent® • ECI: „phase inversion“ • 5 fps • Examples: frames 1, 2, 4, 8 out of 16 Ultrasonic Assessment of Perfusion Conditions Ruhr-University 11/13 RF Engineering Institute
Results c 0 (blood volume) 0 p (perfusion) 100 0 Ultrasonic Assessment of Perfusion Conditions Ruhr-University 12/13 RF Engineering Institute 2
Conclusions and Outlook • 2 different approaches for the assessment of perfusion – analysis of the response to a bolus injection of contrast qualitative visualization of perfusion, slow, robust – analysis of ultrasound-induced decay semi-quantitative visualization of perfusion, fast • Further in vivo measurements necessary to evaluate both techniques Ultrasonic Assessment of Perfusion Conditions Ruhr-University 13/13 RF Engineering Institute
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