Evaluation of Precision in Optoacoustic Tomography for Preclinical Imaging in Living Subjects

Abstract

Optoacoustic tomography (OT) is now widely used in preclinical imaging; however, the precision (repeatability and reproducibility) of OT has yet to be determined. We used a commercial small-animal OT system. Measurements in stable phantoms were used to independently assess the impact of system variables on precision (using coefficient of variation, COV), including acquisition wavelength, rotational position, and frame averaging. Variables due to animal handling and physiology, such as anatomic placement and anesthesia conditions, were then assessed in healthy nude mice using the left kidney and spleen as reference organs. Temporal variation was assessed by repeated measurements over hours and days both in phantoms and in vivo. Sensitivity to small-molecule dyes was determined in phantoms and in vivo; precision was assessed in vivo using IRDye800CW. OT COV in a stable phantom was less than 2.8% across all wavelengths over 30 d. The factors with the greatest impact on signal repeatability in phantoms were rotational position and user experience, both of which still resulted in a COV of less than 4% at 700 nm. Anatomic region-of-interest size showed the highest variation, at 12% and 18% COV in the kidney and spleen, respectively; however, functional SO measurements based on a standard operating procedure showed an exceptional reproducibility of less than 4% COV. COV for repeated injections of IRDye800CW was 6.6%. Sources of variability for in vivo data included respiration rate, degree of user experience, and animal placement. Data acquired with our small-animal OT system were highly repeatable and reproducible across subjects and over time. Therefore, longitudinal OT studies may be performed with high confidence when our standard operating procedure is followed.

Quantitative photoacoustic imaging study of tumours in vivo: baseline variations in quantitative measurements

“…The inter-and intra-tumour CoV for the CAL R tumours due the re-positioning of the animal (Table S2) were >22.0±21.2% and >26.5±8.3%, respectively, for all the parameters (Hb, HbO 2 , HbT and sO 2 ), hence similar to those obtained for the study without re-positioning the animal (see Table S1), over a 75 minute period, apart from animal 4. This also suggests that anaesthesia is the main experimental factor that contributes for the temporal variability of the signal, as found by Joseph et al [44].…”

“…This reflects a high variation in the measured signal of each animal, expected due to the increasing trend in haemoglobin and blood sO 2 over time. Joseph et al (2017) [44] studied the repeatability and reproducibility of PAI with the same system as that used here in the left kidney and spleen of 8-12 week old mice (n=7), acquiring images over a period of 90 minutes, under isoflurane anaesthesia. The authors found a steady increasing trend in HbT and blood sO 2 over the 90 minute imaging acquisition.…”

Photoacoustic imaging for the prediction and assessment of response to radiotherapyin vivo

“…Nordsmark and Overgaard [46], while investigating the relationship between hypoxia and tumour control after radiotherapy, showed that oxygenation in tumours, measured using Eppendorf oxygen electrodes, was independent of total haemoglobin levels, obtained from a venous blood sample acquired before the treatment. Also, Joseph et al [47] found that a higher coefficient of variation (CoV) was expected for haemoglobin than for sO 2 over either short periods of time (hours) or longer ones (days), as we have confirmed in a previous study [48]. This higher CoV makes Hb, HbO 2 and HbT less predictive parameters than blood sO 2 .…”

Photoacoustic molecular rulers based on DNA nanostructures

“…47 For all the measurements, the phantoms were maintained at 34°C inside the . CC-BY-NC-ND 4.0 International license peer-reviewed) is the author/funder.…”

“…47 All the reagents for phantoms fabrication were purchased from Sigma Aldrich (Sigma-Aldrich Co.) unless otherwise stated. The DNA nanostructures were suspended inside sealed thin walled plastic tubes (0.3 cm diameter) that were placed at the center of the cylindrical phantoms (2 cm diameter) as shown in Figure S10b.…”