Purpose: To develop a new MRI method to detect and characterize brain abscesses using the CEST contrast inherently carried by bacterial cells, namely bacCEST. Methods: Bacteria S. aureus (ATCC #49775) and F98 and 9L glioma cells were injected stereotactically in the brains of F344 rats to form abscesses and tumors. The CEST signals of brain abscesses (n=4) and tumors (n=7) were acquired using 2 B1 values (i.e., 1 and 3μT) and compared. The bacCEST signal of the brain abscesses in the rats (n=3) receiving ampicillin (intraperitoneal injection 40mg/kg twice daily) was acquired before, 4 and 10 days after the treatment. Results: The bacCEST signal of S. aureus was characterized in vitro as a strong and broad signal in the range of 1 to 4ppm, with the maximum contrast occurring at 2.6ppm. The CEST signal in S. aureus-induced brain abscesses was significantly higher than that of contralateral parenchyma (p=.003). Moreover, thanks to their different B1 independence, brain abscesses and tumors could be effectively differentiated (p=.005) using ΔCEST(2.6ppm, 3μT-1μT), defined by the difference between the CEST signal (offset=2.6ppm) acquired using B1=3μT and that of 1μT. In treated rats, bacCEST MRI could detect the response of bacteria as early as 4 days after the antibiotic treatment (p=.035). Conclusion: BacCEST MRI provides a new imaging method to detect, discriminate, and monitor bacterial infection in deep-seated organs. Because no contrast agent is needed, such an approach has a great translational potential for detecting and monitoring bacterial infection in deep-seated organs.
- Bacterial infection
- Brain abscess
ASJC Scopus subject areas
- Radiology Nuclear Medicine and imaging