ASL-BIDS, the brain imaging data structure extension for arterial spin labeling

A recent paper in Scientific Data describes ASL-BIDS, the extension of BIDS (Brain Imaging Data Structure) for arterial spin labeling.  BIDS is a versatile standard for diverse types of neuroimaging data, originating from the INCF Taskforce for Neuroimaging Data Sharing and endorsed by INCF as a standard in 2018. The ASL extension was released in BIDS 1.5.0, and in this first version it is mainly aimed at clinical ASL applications, implementing recommendations made in a 2015 consensus paper written by the ISMRM perfusion study group and the European consortium for ASL in dementia.

Arterial spin labeling (ASL) is a non-invasive MRI technique that allows for quantitative measurement of cerebral perfusion. Incomplete or inaccurate reporting of acquisition parameters complicates quantification, analysis, and sharing of ASL data, particularly for studies across multiple sites, platforms, and ASL methods. There is a strong need for standardization of ASL data storage, including acquisition metadata. 

The extension faced two main challenges compared to existing BIDS data types. Firstly, large variability exists between vendors, scanners, and research labs in the implementation, reconstruction, and export of ASL data. Secondly, ASL measures a quantifiable metric. This renders the accurate reporting of scale slopes essential for quantification, reproducibility, and comparability of ASL studies.

While ASL can provide information relating to functional activation of the brain, it is most commonly used to measure a fundamental physiological parameter (perfusion) that reflects baseline metabolic demand rather than transient neural activity, distinguishing it from the existing BIDS data type ‘func’. Therefore, a new perfusion data type ‘perf’ for ASL-related data was defined, which can also be used for other perfusion-related BIDS extensions in the future, such as dynamic susceptibility contrast (DSC) MRI.

In addition, several BIDS fields were added during the development phase of ASL-BIDS, serving the needs of both clinical users and advanced sequence developers, and several non-required pre-existing BIDS fields were defined as required for ASL.

Several resources are already available: the BIDS extension for ASL has been implemented in the BIDS validator, which can be used to test BIDS compatibility. Several DICOM to BIDS conversion tools and ASL processing software packages have adopted ASL-BIDS, and five example ASL datasets in BIDS format are freely accessible on Github and (in citable format) on OSF.

Resources:
Paper: https://www.nature.com/articles/s41597-022-01615-9
BIDS Documentation related to ASL: https://bids-specification.readthedocs.io/en/stable/appendices/arterial-spin-labeling.html