High frequency ultrasound in monitoring organ viability for transplantationRoxana Vlad1, Anoja Giles1, 2, G.J Czarnota1, 2, J.W. Hunt1, 2, M.D. Sherar1, 2 and M.C. Kolios1, 3

1Department of Medical Biophysics, University of Toronto; 2Ontario Cancer Institute, 3 Department of Mathematics, Physics and Computer Science, Ryerson University, Toronto, Ontario, Canada

OBJECTIVEHigh frequency ultrasound (HFU) can be used to detect structural changes in cells and tissues during cell death. The changes in the ultrasound signal intensity and frequency spectrum are related to the changes in size, spatial distribution and acoustic impedance of the tissue scatterers. We hypothesize that the mechanism behind this ultrasonic detection is the condensation and fragmentation that cell nuclei undergo during cell death. Our proposal is to use high frequency ultrasound and spectroscopy analysis techniques to follow the decay of organs once they are harvested for the purpose of transplantation. The ultimate goal is to assess organ viability for transplantation procedures. METHODSLivers and kidneys from Wistar rats are surgically excised, flushed with University of Wiscosin solution and stored at 4C for a specified period of time or left to decay at room temperature. High-resolution images and the corresponding raw (radio frequency) RF data are collected every one/two hours from a region of interest located in the transducer focal zone. At the end of the experiment, samples are fixed for Hematoxylin & Eosin (H&E) and TUNEL staining.

The backscatter intensity increased by 5-16 dBr between freshly excised organs imaged at 0h and the organs imaged after 10h (left to decay at room temperature), Fig 3 and Fig 7. This increase is consistent with nuclei condensation and fragmentation observed in H&E and Tunel staining of organs left to decay, Fig 2 and Fig 6.

CONCLUSIONS The preliminary results show a certain

increase in backscatter intensity comparing unpreserved organs to preserved ones at the same time points. This increase in backscatter intensity is temperature and time dependent (preserved organs are imaged at 4C and organs left to decay at 20-22C, room temperature) and the values range in 2-16 dBr interval, Fig 4, 5 and Fig 7.

• The backscatter intensity increase is more pronounced in the interval of 20 to 30 MHz with a peak at 30 MHz, Fig 3 and Fig 4.

• HFU can be considered as a tool for detecting cell death and/or other changes occurring during organ decay.

Acknowledgments:The Whitaker FoundationDr. Sherar’s lab

The VS-40B ultrasound imager employs two transducers f/2 and f/3 with operating frequency of 40MHz and a relative bandwidth of 93% and 95%, respectively. RF signals are stored digitally at a sampling rate of 500 MHz associated with the captured image. Analysis of normalized spectra on collected RF data is carried out, Fig 1.

RESULTS

Fig 2, Liver Decay

Liver Decay vs. Liver Preservation in University of Wisconsin solution

The normalized spectra are correlated with captured images at different time points and with (H&E) and Tunel staining of analyzed organs, taken at the beginning and at the end of the experiments.

Fig 6, Kidney Decay

Frequency, MHz

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wer

, dB

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Fig 5, UW 8°C UW 21°C Decay 21°C

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Fig 3 Frequency, MHz Fig 4

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Decay Preservation0h 4h

6h 10h

Decay 21C

UW 21C

UW 8C

Decay vs. Preservation, 0h and 10h

Fig 7, Decay Preservation

4h 8 h 10h

0h 1h 2h

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Fig 1