Multi-frame DICOM and cine loops on a phone
A multi-frame DICOM is a single file that contains many images, called frames, one after another. When those frames are shown in sequence they form a short moving clip, known as a cine loop. This format is common for angiography and ultrasound, where the point is to see something change over time.
One file, many frames
Most CT and MRI studies use one file per slice. A multi-frame file is different. It stores a whole sequence inside one .dcm, and a tag in the file records how many frames there are.
The frames in a cine loop are usually the same view captured again and again over a few seconds. A scrolling stack of CT slices moves through space. A cine loop stays at one place and moves through time.
Some newer CT and MRI systems also write multi-frame files, where the frames are slices of a stack rather than moments in time. The file structure is the same, only the meaning of the frames changes.
Where you meet cine loops
- Angiography. A series of X-ray frames taken while contrast moves through vessels.
- Ultrasound. Short clips recorded during the examination.
- Other moving studies. Some fluoroscopy and nuclear medicine files are also stored as multi-frame.
If you receive a disc from a procedure like this, the important images are often a few large files rather than hundreds of small ones.
Why these files are large
Every frame carries image data, so a clip of 100 frames is about 100 images in one file. Files of tens or hundreds of megabytes are normal. Some are compressed inside the file, others are not.
This has practical effects on a phone:
- opening takes longer than a single slice
- copying or sharing the file by message or email can hit size limits
- an old or low-memory device may take a moment to load every frame
If a file refuses to open, size and compression are among the usual suspects. See DICOM file won’t open: causes and fixes.
Playback speed
A multi-frame file may record the intended speed, either as a time between frames or as a frames-per-second value. A viewer can use this to play the clip at the pace it was recorded. If that value is missing, the viewer has to choose a default rate.
Because of this, the same clip can appear faster or slower in different programs. A slow or fast playback does not mean the file is damaged, and it does not change the data.
Controls that matter
Watching a loop run is only part of the job. These controls are what make a cine loop useful:
- Play and pause, to stop on a moment you want to look at.
- Frame stepping, to move forward or back one frame at a time.
- A scrubber, a slider you drag to jump to any point in the clip.
- Zoom and pan, to enlarge part of the frame while paused.
Stepping frame by frame is often easier than watching in real time, since at full speed many details pass in a fraction of a second.
Opening one on a phone
On Android you can open a multi-frame file directly, without a PC. If you only have the disc, copy its files to a computer first, then move them to the phone. For general steps on opening a .dcm file, see How to open a DICOM file without software, and for what the format is, What is a DCM file?.
Radix DICOM plays multi-frame cine loops with play and pause, frame stepping and a scrubber, and you can pinch to zoom and pan. It works offline and does not upload the file. It is not a medical device and is not for diagnosis.
What a loop does not tell you
A cine loop is a recording. Watching it on a phone does not tell you anything about a person’s health, and playback quality on a small screen is not the same as a hospital workstation. The doctors who performed and review the procedure are the ones who interpret it. Any decision based on the images belongs to the patient’s doctor.