Which File Formats Open in Our Knee MRI and X-ray Viewer

Archive formats

If your scan came as one big compressed file, drop it directly into the viewer — we unpack it in your browser.

• ZIP — the most common format on hospital CDs and patient-portal downloads
• TAR — common for research datasets
• .tar.gz and .tgz — TAR + GZIP compressed

DICOM transfer syntaxes

The technical format used to encode pixel data inside a DICOM file. Our viewer decodes every common transfer syntax used by clinical scanners.

• Implicit VR Little Endian (1.2.840.10008.1.2)
• Explicit VR Little Endian (1.2.840.10008.1.2.1)
• JPEG Lossless (1.2.840.10008.1.2.4.70)
• JPEG Extended 12-bit (used by i-CAT dental CBCT)
• RLE Lossless
• 8-bit, 12-bit, and 16-bit pixel data
• MONOCHROME1 and MONOCHROME2 photometric interpretations

NIfTI (research / converted scans)

NIfTI (Neuroimaging Informatics Technology Initiative) is the format used by most research and post-processing tools. If you ran your scan through a pipeline like FreeSurfer or fastMRI, you likely have a NIfTI file.

• .nii — uncompressed NIfTI volume
• .nii.gz — GZIP-compressed NIfTI (most common)

What a knee imaging study usually contains

A typical outpatient knee referral produces several series rather than one image. Radiologists lean on sagittal and coronal proton-density fat-saturated sequences to trace meniscal tears and cartilage surfaces, while an axial proton-density series covers the patellofemoral joint and trochlear groove. T2-weighted and STIR sequences highlight bone marrow oedema after a twisting injury or a tibial plateau bruise, and a T1-weighted series is the standard way to check graft continuity and marrow signal months after an ACL reconstruction. Whether the study was acquired at 1.5T or 3T changes contrast and noise, not the file format — both arrive as ordinary DICOM, and the fat-suppressed sequences (often labelled “PD FS” on the disc) are usually what a knee surgeon reads first for meniscal or ligament injury.

Plain film series are just as common in this folder. A standing weight-bearing AP view and a Rosenberg flexion view reveal joint-space narrowing that a supine scan would hide, a skyline or merchant view isolates the patellofemoral joint, and a lateral view is what a surgeon measures patellar height from. When a tibial plateau fracture needs mapping before fixation, or when a surgeon needs the exact tunnel position after a ligament reconstruction, a dedicated knee CT usually joins the folder alongside the MRI. Many of these post-operative CTs use a metal-artifact-reduction reconstruction to keep the bone around a plate or a total knee prosthesis readable. MRI, X-ray, and CT are all DICOM underneath, and our viewer opens every one of them the same way.

How a knee study usually reaches you

Most knee studies leave the imaging center in one of three shapes. Hospital-issued CDs and DVDs still ship with a DICOMDIR index file sitting alongside folders of numbered slices — drop the whole disc folder into the viewer and it reads the DICOMDIR to figure out which series is which. Patient portals more often hand you a single ZIP archive bundling every series from the visit; ours unpacks that archive locally rather than sending it anywhere. If your surgeon ran the scan through a research or post-processing pipeline, you may instead have NIfTI exports — one volume per series, with the original DICOM metadata stripped out. Whichever shape it takes, when several series are bundled together the sagittal proton-density stack is usually the one worth loading first, since most meniscal and cartilage reads are based on it. Occasionally a clinic emails a single series as an attachment or hands you a USB drive instead of a disc — the viewer treats those the same as a CD folder, since the DICOM files themselves are identical regardless of the medium they travelled on.

Slice thickness and 3D rendering for a knee study

Whether a knee series reconstructs cleanly in 3D or in a different plane comes down to how it was acquired, not its file extension. A routine clinical knee MRI is typically sliced 3 to 4 millimeters apart with small gaps between slices — fine for reading on the original imaging plane, but it produces a blocky, stair-stepped volume when reformatted or rendered in 3D. Thin, truly isotropic sequences behave differently: 3D DESS and cartilage-mapping sequences such as CUBE or SPACE are acquired sub-millimeter in every direction, so they reconstruct into smooth sagittal, coronal, and axial views and hold up well in the volume renderer. The trade-off is scan time: an isotropic 3D sequence takes longer to acquire than a standard 2D fast spin-echo sequence, which is why many clinical protocols still mix a thick-slice 2D sagittal PD with a single thin isotropic sequence rather than acquiring everything at high resolution. A single knee radiograph, by contrast, is one flat 2D projection — there is no depth to reconstruct, so it displays as an image rather than a rotatable volume no matter how it was exported.

Compatibility at a glance

Guides: private viewing and 3D rendering for knee studies

When a knee study still won't open

A handful of knee studies still trip up any browser-based viewer. Encrypted hospital CDs — mostly from older European PACS systems — need an unencrypted copy from your imaging center's release-of-records process before any viewer, ours included, can read them. A knee MRI split across two discs because the sagittal and axial series didn't fit on one CD should be combined into a single ZIP before you drop it in, so the viewer can match series across both halves. Studies anonymized before being handed to you — with the patient name and date of birth stripped from the DICOM header — still open fine, since the viewer only needs the pixel data and imaging geometry, not the identifying fields. If a series still won't load, check that what you dropped is the DICOM folder itself — with its DICOMDIR and numbered slice files — and not just the disc's bundled Windows viewer program.