Cross-validation of Input Functions Obtained by H2 15O PET Imaging of Rat Heart and a Blood Flow-through Detector

Purpose

Positron emission tomography (PET) with ¹⁵O-labeled water (H₂ ¹⁵O) facilitates the visualization and quantification of blood flow in clinical investigations and also in small animals. The quantification of blood flow requires an input function, which is generally obtained by measuring radioactivity in arterial blood withdrawn during PET scanning. However, this approach is not always feasible, because abundant blood sampling may affect the physiological process being measured. The purpose of the present study was to develop and cross-validate two methods, namely, a blood- and an image-based method for obtaining the input function for blood flow studies from rat H₂ ¹⁵O PET.

Methods

The study material consisted of two separate groups of rats. Group 1 rats were imaged twice by a high-resolution research tomograph PET camera at resting condition for a test?Cretest study (n?=?4), and group 2 rats were imaged with and without adenosine infusion for a rest?Cstress study (n?=?4). In group 1, radioactivity concentration in arterial blood was measured with a new flow-through detector during imaging and a blood-based input function was obtained. The image-based input function was estimated using time-activity curves from the left ventricle and myocardial regions. To validate the two input function methods, myocardial blood flow (MBF) and cerebral blood flow (CBF) were computed, and the methods were tested for reproducibility (test?Cretest study) and changes (rest?Cstress study).

Results

The blood- and image-based input functions were similar, and the corresponding CBF values differed only by ?6.9?±?8.1%. In the test?Cretest study, both MBF and CBF showed good reproducibility, and in the rest?Cstress study, adenosine significantly increased both MBF (P?=?0.035) and CBF (P?=?0.029), compared with the resting condition.

Conclusion

It is possible both to measure the input function from rat arteria femoralis during H₂ ¹⁵O PET imaging and to estimate the input function from rat H₂ ¹⁵O PET images, thereby facilitating the assessment of blood flow in organs visible in PET images.