Abstract
The design and testing of a new, fully automated, calibration approach is described. The process was used to calibrate an image-guided diffuse optical spectroscopy system with 16 photomultiplier tubes (PMTs), but can be extended to any large array of optical detectors and associated imaging geometry. The design goals were accomplished by developing a routine for robust automated calibration of the multi-detector array within 45 minutes. Our process was able to characterize individual detectors to a median norm of the residuals of 0.03 V for amplitude and 4.4 degrees in phase and achieved less than 5% variation between all the detectors at the 95% confidence interval for equivalent measurements. Repeatability of the calibrated data from the imaging system was found to be within 0.05 V for amplitude and 0.2 degrees for phase, and was used to evaluate tissue-simulating phantoms in two separate imaging geometries. Spectroscopic imaging of total hemoglobin concentration was recovered to within 5% of the true value in both cases. Future work will focus on streamlining the technology for use in a clinical setting with expectations of achieving accurate quantification of suspicious lesions in the breast.
Highlights
Image-guided optical spectroscopy is a non-invasive complement to dynamic contrast enhanced MR imaging (DCE-MRI) of breast that produces functional maps of tissue physiology, and could be used to inform decisions about magnetic resonance (MR)-guided biopsy
The imaging system is housed in the MR console room and 12 m fiber bundles with 4 mm working optical diameters are passed through a custom penetration panel in the wall to enter the MR scanner room
photomultiplier tubes (PMTs) typically exhibited a linear response over four orders of magnitude for amplitude and nearly the same for phase, this range was larger when the imaging geometry involved path length variations
Summary
Image-guided optical spectroscopy is a non-invasive complement to dynamic contrast enhanced MR imaging (DCE-MRI) of breast that produces functional maps of tissue physiology, and could be used to inform decisions about magnetic resonance (MR)-guided biopsy. A frequency domain optical imaging system was developed to collect amplitude and phase data concurrently with the patient’s DCE-MRI exam [1,2]. Near infrared spectroscopy (NIRS) systems exploit detectors that have variable gain settings, and require careful calibration in order to ensure the data is robust between scans and from day to day. Calibration of these systems has been a difficult and time-consuming process [4,5,6], which was adequate during development, but not sufficient for day-to-day use. The automation simplifies standardization and quality control between scans, and is expected to lead to more accurate quantification of the relevant tissues of interest when the system is transported to other sites
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