Influence of residual oxygen-15-labeled carbon monoxide radioactivity on cerebral blood flow and oxygen extraction fraction in a dual-tracer autoradiographic method

• Published in: Annals of nuclear medicine Vol. 23; no. 4; pp. 363 - 371
• Main Authors: Iwanishi, Katsuhiro, Watabe, Hiroshi, Hayashi, Takuya, Miyake, Yoshinori, Minato, Kotaro, Iida, Hidehiro
• Format: Journal Article
• Language: English
• Published: Japan Springer Japan 01-06-2009; Springer Nature B.V
• Subjects: Autoradiography; Carbon Monoxide - chemistry; Carbon Monoxide - metabolism; Cerebrovascular Circulation; Computer Simulation; Humans; Imaging; Medicine; Medicine & Public Health; Models, Biological; Nuclear Medicine; Original Article; Oxygen - metabolism; Oxygen Radioisotopes - chemistry; Oxygen Radioisotopes - metabolism; Positron-Emission Tomography; Radioactive Tracers; Radioactivity; Radiology; Sensitivity and Specificity; Staining and Labeling; Subtraction Technique; OEF; Carbon monoxide; CBV; PET
• ISSN: 0914-7187; 1864-6433
• DOI: 10.1007/s12149-009-0243-7

Objective
Cerebral blood flow (CBF), cerebral metabolic rate of oxygen (CMRO
2
), oxygen extraction fraction (OEF), and cerebral blood volume (CBV) are quantitatively measured with PET with
15
O gases. Kudomi et al. developed a dual tracer autoradiographic (DARG) protocol that enables the duration of a PET study to be shortened by sequentially administrating
15
O
2
and C
15
O
2
gases. In this protocol, before the sequential PET scan with
15
O
2
and C
15
O
2
gases (
15
O
2
–C
15
O
2
PET scan), a PET scan with C
15
O should be preceded to obtain CBV image. C
15
O has a high affinity for red blood cells and a very slow washout rate, and residual radioactivity from C
15
O might exist during a
15
O
2
–C
15
O
2
PET scan. As the current DARG method assumes no residual C
15
O radioactivity before scanning, we performed computer simulations to evaluate the influence of the residual C
15
O radioactivity on the accuracy of measured CBF and OEF values with DARG method and also proposed a subtraction technique to minimize the error due to the residual C
15
O radioactivity.
Methods
In the simulation, normal and ischemic conditions were considered. The
15
O
2
and C
15
O
2
PET count curves with the residual C
15
O PET counts were generated by the arterial input function with the residual C
15
O radioactivity. The amounts of residual C
15
O radioactivity were varied by changing the interval between the C
15
O PET scan and
15
O
2
–C
15
O
2
PET scan, and the absolute inhaled radioactivity of the C
15
O gas. Using the simulated input functions and the PET counts, the CBF and OEF were computed by the DARG method. Furthermore, we evaluated a subtraction method that subtracts the influence of the C
15
O gas in the input function and PET counts.
Results
Our simulations revealed that the CBF and OEF values were underestimated by the residual C
15
O radioactivity. The magnitude of this underestimation depended on the amount of C
15
O radioactivity and the physiological conditions. This underestimation was corrected by the subtraction method.
Conclusions
This study showed the influence of C
15
O radioactivity in DARG protocol, and the magnitude of the influence was affected by several factors, such as the radioactivity of C
15
O, and the physiological condition.