Here we consider the problem of applying susceptibility distortion correction to EPI imaging data. We derive an efficient algorithm for simultaneously correcting for head motion and susceptibility distortions.
Background
Consider a collection of MRI scans of a human brain. When collected, each image is in the "scanner space", which is to say that the elements of the data arrays (voxels) correspond to locations inside an MR scanner. When comparing images for the same subject, this space is generally unhelpful, as subjects may move within the scanner, and the scanner operator may select a different location within the scanner to consider the origin $(0, 0, 0)$.
Therefore images must be brought into register with one another. Generally, one uses successive approximations of transformations, such as rotations and translations, to minimize a cost function. The resulting transformation may be used to transform coordinates in one image to the equivalent coordinates in another.
Images contain an internal affine transformation that translates from indices in the data matrix into world coordinates, conventionally in millimeters (mm) right, anterior and superior of some origin. Because the world coordinate space is abstracted from the details of the data array, it is convenient to represent transformations between images as transformations between their world coordinates, not their array indices.
Head motion
Authors: Peer Herholz, Oscar Esteban, Chris Markiewicz, Ariel Rokem, and Franco Pestilli
Date: 2023-07-21
Abstract
In this document, we propose a general principle for developing BIDS extension proposals for derivative data. The goal is to establish consensus so that parts of BEPs that propose terms in line with this document will be considered accepted in principle. The proposal is to ask feedback from the community, provide a timeline for the discussion, and settle on a decision making process. At the end of the timeline we request that a decision be reached. The proposal is RECOMMENDED not REQUIRED in that BEPs would be allowed to deviate when deemed necessary.
Problem statement
In working through BEPs 12 and 16, we have identified a repeated pattern in generating derivatives within several imaging modalities' workflows where:
We require a reference map that is used to encode spatial features and parameters. There is an antecedent of this in BIDS with BEP23 (see below). In that BEP, the proposed naming takes the pattern _<suffix>ref (e.g., _boldref, _dwiref, etc.), and that solution has been suggested as a possibility in issue #1532 of the spec repository.
sub-X/func/sub-X_task-Y_run-Z_desc-hmc_boldref.nii.gz # BOLD contrast
sub-X/func/sub-X_task-Y_run-Z_desc-coreg_boldref.nii.gz # aligned to hmcref, use sbref and fieldmaps, if possible
sub-X/func/sub-X_task-Y_run-Z_from-orig_to-boldref_mode-image_xfm.txt
sub-X/func/sub-X_task-Y_run-Z_from-boldref_to-T1w_mode-image_xfm.txt
sub-X/func/sub-X_task-Y_run-Z_from-T1w_to-boldref_mode-image_xfm.txt
sub-X/func/sub-X_task-Y_run-Z_from-fmap_to-boldref_mode-image_xfm.txt # MI metric
Dependency structure
graph TB;
subgraph Head motion correction
bold.nii --> desc-hmc_boldref.nii;
Option 1: Dense dereferenced objects (via Taylor)
columns.yaml + values.yaml
type__eeg_channels:
name: type
display_name: Channel type
description: |
Type of channel; MUST use the channel types listed below.
Note that the type MUST be in upper-case.
type: string
enum:
The following API provides the basic data structures needed to represent a BIDS
dataset. It aims to be simple enough to bear multiple implementations.
Index = PaddedInt
Value = str
Entity = Literal['subject', 'session', ...]
class Schema:
"""Representation of the state of BIDS schema
The checklist format
The file checklists/checklist.json contains the description
of the bronze, silver and gold tier checklists, which
are rendered by the application in interactive/.
For example, this snippet:
{
"id": "bronze_doc_1",
"prompt": "Landing page (e.g., GitHub README, website) provides a link to documentation and brief description of what program does",
This dataset is a BIDS Derivatives dataset resulting from running fMRIPrep on
[{{ dataset_id }}](https://openneuro.org/datasets/{{ dataset_id }}).
Methods
fMRIPrep documentation can be found on https://fmriprep.org/en/stable/.
For a complete description of the methods applied to these data, see logs/CITATION.md.
This boilerplate text is released under CC0, and may be used in whole or part to describe the preparation of these data in publications.
Jobs were submitted using ReproMan in order to improve reproducibility. Output and error logs can be found in .reproman/jobs/local/.
jbwexler changed 3 years agoView mode Like Bookmark
10 February 2022
State of the BIAP: https://github.com/effigies/nibabel/blob/biap/surfaces/doc/source/devel/biaps/biap_0009.rst
Ready for final(ish) comment and move on to implementation.
28 January 2022
Attending: Chris, Joshua Teves
MNE/STC