From the scanner

One phantom, six contrasts

Acquired on the AltraMRI 0.4T system on 9 November 2026. A three-media phantom run through the standard fore-foot protocol: pilot, proton density, T1, T2, T2* and STIR, twelve 5 mm slices each, 170 mm field of view, 1 mm in-plane voxels. Rendered from the console's reconstructions, windowed per image, with a millimetre scale on each.

Three-plane gradient echo pilot of the phantom: a transverse view of the disc with tubes in cross-section, and two longitudinal views showing the tubes along their length
Three-plane pilot, gradient echo, TR 70 ms, TE 7 ms, 128 × 128 over 192 mm (1.5 × 1.5 × 5 mm). The first scan of the exam, under a minute.

The phantom

Three media, three tissues

A disc of doped agar carrying tubes of pure water and MCT oil. Each medium stands in for a tissue the fore-foot protocol has to separate.

Pure water

The small round tubes

Free fluid: joint effusion, a cyst, oedema

Very long T1 (seconds) and long T2. Saturated and dark whenever TR is short; the brightest thing in the phantom on T2 and STIR.

MCT oil

The larger tubes around some of the water tubes

Fat: the digital cushion, marrow

Short T1, so bright on every T1-weighted image. Its inversion time of roughly 90 ms matches fat in the equine limb at 0.4T, so the STIR nulls it.

Agar, copper sulphate, salt

The bulk of the disc

Muscle and soft tissue

Doped to the T1 and T2 of muscle. Recovers between repetitions, so intermediate grey on T1 and proton density, and darker than fluid on T2.

Same slice, six sequences

How the three media rank

Slice 5 of 12 from each scan, cropped to the disc. Read the water tubes first, then the oil rings, then the agar between them.

Proton density spin echo image of the phantom
Proton density Spin echoTR 1000 ms · TE 24 ms · 170 × 170, 1.0 × 1.0 × 5 mmWater darkOil brightAgar intermediateAt TR 1000 ms the water is still saturated; the doped agar has recovered. The oil, with the shortest T1, is brightest.
T1-weighted spin echo image of the phantom
T1-weighted Spin echoTR 480 ms · TE 20 ms · 170 × 170, 1.0 × 1.0 × 5 mmWater darkOil brightAgar intermediateThe classic T1 picture: fat-like oil bright, fluid black, tissue-like agar in between.
T1-weighted gradient echo image of the phantom
T1-weighted Gradient echoTR 116 ms · TE 9 ms · 170 × 170, 1.0 × 1.0 × 5 mmWater darkOil brightAgar intermediateSame contrast ordering as the spin echo at a fraction of the TR. The lower matrix is the fast variant.
T2*-weighted gradient echo image of the phantom
T2*-weighted Gradient echoTR 136 ms · TE 9 ms · 170 × 170, 1.0 × 1.0 × 5 mmWater intermediateOil intermediateAgar brightEvery tube wall draws a dark ring: the susceptibility step at each plastic interface, which a spin echo refocuses and a gradient echo does not.
T2-weighted fast spin echo image of the phantom
T2-weighted Fast spin echoTR 2000 ms · TE 84 ms · 168 × 180, 1.0 × 0.9 × 5 mmWater brightOil brightAgar darkFluid lights up and the muscle-like agar falls away. The oil stays bright, as fat does on fast spin echo.
Fluid-sensitive, fat-suppressed stir fast spin echo image of the phantom
Fluid-sensitive, fat-suppressed STIR fast spin echoTR 3160 ms · TE 28 ms · 168 × 180, 1.0 × 0.9 × 5 mmWater brightOil nulledAgar intermediateThe inversion time is set to null the oil, and the rings go black while the water tubes are the brightest objects in the image. This is the contrast that finds fluid in bone.
SequenceTR / TEAcquired matrix, voxelWater (fluid)MCT oil (fat)Doped agar (muscle)
Proton density Spin echo1000 / 24 ms170 × 170, 1.0 × 1.0 × 5 mmdarkbrightintermediate
T1-weighted Spin echo480 / 20 ms170 × 170, 1.0 × 1.0 × 5 mmdarkbrightintermediate
T1-weighted Gradient echo116 / 9 ms170 × 170, 1.0 × 1.0 × 5 mmdarkbrightintermediate
T2*-weighted Gradient echo136 / 9 ms170 × 170, 1.0 × 1.0 × 5 mmintermediateintermediatebright
T2-weighted Fast spin echo2000 / 84 ms168 × 180, 1.0 × 0.9 × 5 mmbrightbrightdark
Fluid-sensitive, fat-suppressed STIR fast spin echo3160 / 28 ms168 × 180, 1.0 × 0.9 × 5 mmbrightnulledintermediate

What it shows

Three things to take from the phantom

The ordering is right

Across six sequences the three media rank exactly as fluid, fat and muscle rank in the limb. That is the test a contrast phantom is built for.

STIR separates fluid from fat

With oil at the inversion null and water at its brightest, the fat-suppressed image is the one that will show bone oedema against marrow fat.

Spin echo and gradient echo behave as they should

Spin echo refocuses the susceptibility at every tube wall; gradient echo does not and draws the rings. Both families are available in every plane.

Through the stack

Twelve slices, two of the sequences

T2-weighted fast spin echo: four consecutive slices through the phantom
T2-weighted fast spin echo. Slices 5 to 8 of 12. TR 2000 ms, TE 84 ms, 168 × 180 acquired, 1.0 × 0.9 × 5 mm.
STIR fast spin echo: four consecutive slices through the phantom
STIR fast spin echo. Slices 5 to 8 of 12. TR 3160 ms, TE 28 ms, 168 × 180 acquired, 1.0 × 0.9 × 5 mm. Oil nulled, water bright.

Reconstructions from the AltraMRI console, 9 November 2026, windowed per image; standard reconstruction, no further processing. Scales in millimetres from the acquisition field of view. Matrices are as acquired: readout oversampling and navigator echoes are not counted. Phantom images; no horse has been imaged on the 0.4T system yet. The phantom was first imaged through the full protocol on 8 November 2026 and re-acquired on 9 November with the standard fast spin echo readout.

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