One-line definitions of the MRI and dataset terms used across this documentation. See Concepts & data model for the longer explanation and Taxonomy for the DICOM anchoring of the catalog field names.
| Term | Meaning |
|---|
| k-space | The spatial Fourier transform of the image; what the scanner actually measures. |
| Fully sampled | Every k-space line the field of view requires was acquired → inverse FFT gives a clean image. |
| Undersampled | Lines were skipped to shorten the scan → inverse FFT aliases; needs parallel imaging or compressed sensing. |
Acceleration R | Undersampling factor; R = 3 ≈ one third of the lines acquired (entry.acceleration). |
| ACS | Auto-Calibration Signal — a small fully-sampled block at k-space centre used to estimate coil sensitivities. |
| k-t sampling | An undersampling pattern that varies across time frames (used for dynamic/cine imaging). |
| Partial Fourier | Acquiring slightly more than half of k-space and exploiting its conjugate symmetry. |
| Nyquist rate | The minimum sampling density for alias-free reconstruction of a given field of view. |
| Trajectory | The path through k-space the readout follows: Cartesian (grid), radial, spiral, EPI. |
| Density compensation (DCF) | Per-sample weights that correct for non-uniform k-space sampling density (non-Cartesian). |
| Golden-angle radial | Radial acquisition where successive spokes rotate by ~111.25°, giving near-uniform coverage at any stopping point. |
| Term | Meaning |
|---|
| Receive coil / channel | One element of the scanner's receiver array; each sees the anatomy with a different spatial sensitivity. |
| Virtual coil | A linear (e.g. SVD) combination of physical coils used to compress channel count (entry.coil_data == :derived). |
| Coil sensitivity map | The per-coil complex spatial weighting; needed for parallel-imaging reconstruction. |
| RSS | Root-Sum-of-Squares — the simplest magnitude coil combination (no phase, no de-aliasing). |
| Parallel imaging | Using multiple coils' spatial information to reconstruct undersampled data (SENSE, GRAPPA). |
| SENSE | A parallel-imaging method that solves for the image given coil sensitivity maps. |
| CG-SENSE | Iterative (conjugate-gradient) SENSE; MRIReco's "multiCoil" reconstruction. |
| ESPIRiT | An auto-calibrating method to estimate coil sensitivity maps from an ACS region. |
| Direct / gridding reconstruction | Plain (inverse-FFT or NUFFT) reconstruction with no de-aliasing; MRIReco's "direct". |
| Compressed sensing | Reconstruction that exploits image sparsity to recover undersampled data. |
| Term | Meaning |
|---|
| ISMRMRD / MRD | ISMRM Raw Data — a vendor-neutral HDF5 container for raw acquisitions + an XML experiment header. |
RawAcquisitionData | The type load_raw returns: readout profiles + parsed header (MRIReco.jl docs). |
AcquisitionData | The type a reconstruction package consumes; built by the caller from RawAcquisitionData. |
| Profile / acquisition | One readout line: its complex samples plus an encoding counter (phase-encode line, slice, contrast, …). |
| fastMRI HDF5 layout | The kspace / reconstruction_rss / ismrmrd_header HDF5 schema used by fastMRI and M4Raw. |
| Encoded vs recon matrix | Encoded = as-acquired size (may include oversampling); recon = target image size. |
.mat v7.3 | MATLAB's HDF5-based file format; how CMRxRecon distributes k-space. |
| Term | Meaning |
|---|
| Cine | A movie of the beating heart across the cardiac cycle; the frame axis is time. |
| SAX | Short-axis view — a stack of slices cutting across the left ventricle (base → apex). |
| LAX | Long-axis view — slices along the heart's long axis; the slice axis holds 2-/3-/4-chamber views. |
| LVOT | Left ventricular outflow tract — a third standard cine view. |
| SSFP / bSSFP / TrueFISP | Balanced steady-state free precession — the workhorse cine pulse sequence. |
| T1 / T2 mapping | Quantitative imaging: several differently-weighted images fitted per-pixel to a relaxation curve. |
| MOLLI | Modified Look-Locker Inversion recovery — the standard T1-mapping acquisition scheme. |
| Tagging (SPAMM) | A saturation grid laid over the myocardium; its deformation reveals regional strain. |
| Black-blood | A preparation that nulls flowing-blood signal for vessel-wall / morphology imaging. |
| Flow / phase-contrast | Velocity encoding: image phase is proportional to through-plane blood velocity. |
| Retrospective / prospective gating | Cardiac synchronization: sorting data to the ECG after (retro) or triggering on it before (pro) acquisition. |
| Term | Meaning |
|---|
| GRE / FLASH / spoiled gradient echo | A fast gradient-echo sequence family. |
| TSE / FSE / turbo (fast) spin echo | A multi-echo spin-echo sequence; T1/T2/PD weighting by TE/TR choice. |
| EPI | Echo-planar imaging — a very fast single-shot trajectory used for diffusion and functional MRI. |
| FLAIR | Fluid-Attenuated Inversion Recovery — a TSE variant that nulls CSF signal. |
| VIBE (stack-of-stars) | A 3-D spoiled-GRE sequence; the fastMRI breast data uses a radial stack-of-stars VIBE. |
| PD-weighted | Proton-density weighting (long TR, short TE); the fastMRI knee contrast. |
| Term | Meaning |
|---|
| rtMRI | Real-time MRI — continuous imaging without cardiac/respiratory gating (USC Speech). |
| Vocal tract (pharynx/larynx) | The upper-airway region imaged in speech-production MRI. |
| Volunteer vs patient | entry.cohort — a healthy research subject vs a clinical patient. |
| Low-field MRI | MRI below ~0.5 T (M4Raw is 0.3 T); lower SNR, hence M4Raw's multi-repetition design. |
| Split (train / val / test) | The machine-learning corpus partition (entry.split); an ML concept, not an imaging one. |