Towards quantitative [18F]FDG-PET/MRI of the brain: Automated MR-driven calculation of an image-derived input function for the non-invasive determination of cerebral glucose metabolic rates

Abstract

Absolute quantification of PET brain imaging requires the measurement of an arterial input function (AIF), typically obtained invasively via an arterial cannulation. We present an approach to automatically calculate an image-derived input function (IDIF) and cerebral metabolic rates of glucose (CMRGlc) from the [18F]FDG PET data using an integrated PET/MRI system. Ten healthy controls underwent test-retest dynamic [18F]FDG-PET/MRI examinations. The imaging protocol consisted of a 60-min PET list-mode acquisition together with a time-of-flight MR angiography scan for segmenting the carotid arteries and intermittent MR navigators to monitor subject movement. AIFs were collected as the reference standard. Attenuation correction was performed using a separate low-dose CT scan. Assessment of the percentage difference between area-under-the-curve of IDIF and AIF yielded values within ±5%. Similar test-retest variability was seen between AIFs (9 ± 8) % and the IDIFs (9 ± 7) %. Absolute percentage difference between CMRGlc values obtained from AIF and IDIF across all examinations and selected brain regions was 3.2% (interquartile range: (2.4-4.3) %, maximum < 10%). High test-retest intravariability was observed between CMRGlc values obtained from AIF (14%) and IDIF (17%). The proposed approach provides an IDIF, which can be effectively used in lieu of AIF.

Utility of Absolute Quantification in Non-lesional Extratemporal Lobe Epilepsy Using FDG PET/MR Imaging

“…Patients underwent a brain examination in the interictal state on a fully-integrated PET/MRI system (Siemens Biograph mMR, Erlangen, Germany) as described previously (16). In short, a venous line was established for the injection of the FDG tracer and support foam cushions were placed to brace the subject's head in order to reduce involuntary head movement.…”

“…We have previously developed a methodology that enables the acquisition of a non-invasive image-derive input function (IDIF) based on simultaneously acquired structural and functional data obtained using a fully integrated PET/MR system (16). This methodology takes advantage of the spatial correspondence between structural information of the internal carotid artery (ICA, derived from the MRA sequence) and the PET tracer concentration distribution in and around the ICA (derived from the FDG PET image) in order to apply an exact correction for partial volume distortions.…”

“…This methodology takes advantage of the spatial correspondence between structural information of the internal carotid artery (ICA, derived from the MRA sequence) and the PET tracer concentration distribution in and around the ICA (derived from the FDG PET image) in order to apply an exact correction for partial volume distortions. This approach allows the determination of an accurate arterial input function, which was previously validated against the reference standard of arterial blood sampling (16). Once the arterial input function was derived from the dynamic PET image sequence, parametric images representing MRGlc (in µmol/100 g/min) were calculated using the operational equation implemented for PET by Phelps et al (18), based on the original equation developed by Sokoloff et al (19) and the FDG tracer distribution between 40 and 60 min p.i.…”

“…In order to assess abnormal MRGlc areas in epilepsy patients, the recently described normative database of MRGlc images was used (16). The database includes 20 image volumes derived from a group of healthy controls (5M/5F, median age 27.1 years, IQR = 7.6 years) who were scanned twice using a test-retest design.…”

“…The reason for this omission to fully embrace the potential of PET imaging in clinical applications is the requirement of arterial blood sampling, an invasive procedure not performed routinely. However, with the advent of hybrid imaging, quantification of MRGlc can be achieved noninvasively based on the simultaneous acquisition of both high-resolution anatomical as well as high-sensitive molecular functional data, yielding an image-derived arterial input function from an integrative analysis of PET and MR image data (16). Consequently, this methodological advance enables the determination of absolute regional MRGlc values in clinical routine and might provide added value during diagnostic evaluation of ETLE brain scans (16).…”