(68)Ga-Citrate-PET for diagnostic imaging of infection in rats and for intra-abdominal infection in a patient.

OBJECTIVES: 67Ga-Citrate has been extensively used for infection and inflammation imaging for the past four decades but has limitations. In the present study, we explored the ability of 68Ga-Citrate to detect Staphylococcus aureus (Staph A) infection in rats and further studied its ability to localize intra-abdominal infection in a patient. METHODS: An infection was induced in male Wistar rats by injecting Staph A in the right thigh muscle. In this study a simple method was described for the preparation of 68Ga-Citrate with > 99% yield and purity. 68Ga-Citrate (15 MBq/rat and 150 MBq/patient) was injected intravenously and the images were acquired for 10 min each. RESULTS: 68Ga-Citrate uptake was moderate at the infection lesion within 5 min post injection but intense focal uptake was visualized from 30 min to 6 hr post-injection in rats. Cardiac blood pool and liver activity decreased during the same period of study. In the patient studied, an infected area in the abdomen at the site of recent appendectomy was detected within 30min post-injection of 68Ga-Citrate, which was consistent with CT and microbiology findings. CONCLUSION: A simple method of preparation of 68Ga-Citrate with > 99% yield and purity was described, suitable for routine clinical work. Our results showed 68Ga-Citrate is capable of detecting Staph A infection in rats and an intraabdominal infection in a post-operative patient. These findings indicate the high potential of 68Ga-Citrate for clinical utility.

Potential use of 68Ga-apo-transferrin as a PET imaging agent for detecting Staphylococcus aureus infection.

INTRODUCTION: (67)Ga citrate has been extensively used to detect infection and inflammation since 1971. However, its clinical utility is compromised due to several limitations. The present project explored whether (68)Ga-apo-transferrin ((68)Ga-TF), when prepared in vitro, is a useful agent for positron emission tomography (PET) imaging of bacterial infection. METHODS: An infection was induced in male Wistar rats by injecting 5 × 10(5) CFU units of Staphyococcus aureus in the right thigh muscle. (68)Ga-TF was synthesized by mixing (68)GaCl(3) with apo-transferrin (TF, 2 mg) in sodium carbonate (0.1 M, pH 7.0) and incubating at 40 °C for 1 h. Animals were injected with 10-15 MBq of (68)Ga-TF containing approximately 0.2 mg TF and imaged at different time intervals using Siemens Biograph PET-CT. RESULTS: When (68)Ga-TF were injected in the infected rats, the infection lesion was detectable within 20 min post injection. The biodistribution showed the uptake at the lesion increased with time as shown by significantly increased standard uptake values for up to 4 h post injection. There was a considerable decrease in the background activity during the same period of study, giving higher target-to-muscle ratios. Blood pool activity at 3 h post injection was insignificant. (68)GaCl(3) (when not conjugated to TF) did not localize at the infection lesion up to 120 min post injection. CONCLUSION: The preliminary results suggest that (68)Ga-TF is capable of detecting S. aureus infection in the rat model, within an hour after intravenous injection.

Variation in scanning line source sensitivity: a significant source of error in simultaneous emission-transmission tomography.

Transmission measurement is recommended in order to accurately correct for attenuation in myocardial single-photon emission tomography (SPET) studies. It is important that transmission studies are artefact-free, otherwise the attenuation-corrected SPET studies may also be affected. An assumption in transmission studies is that the measured transmission in air used as a reference scan is valid for any camera orientation. Variation in transmission source sensitivity (both source efficiency and detector sensitivity) with rotation negates this assumption and can produce errors that result in significant reconstructed artefacts. The aim of this study was to investigate the variation in transmission source sensitivity with a view to defining action thresholds for routine quality control tests. Transmission measurements in air were recorded on two commercial scanning line source installations for the 180 degrees arc normally used in myocardial SPET. Significant variation in transmission source sensitivity was observed on one system (exceeding 30%). Comparison was also made with the reference scan recorded at a different time at a fixed angular location. Both systems demonstrated measurable variation between transmission counts and the corresponding reference scan. A simulation study was undertaken using patient data to determine the influence of transmission sensitivity variation on reconstructed myocardial counts. To maintain reconstructed counts to within 15% of that obtained with artefact-free transmission data, the variation in transmission sensitivity with rotation needed to be within 5%. These results have necessitated the addition of quality control procedures and specific maintenance procedures to attempt rectification of the problem. Variation in transmission source sensitivity with rotation is a potential source of error in attenuation-corrected SPET. Steps should be taken to stabilise transmission source mountings so as to minimise this potential source of error.