SPECT acquisition — projections & sinogram

Swing the gamma camera around the patient. Each angle records one projection; the central-slice profile is stacked into the sinogram, shown raw and ramp-filtered. Load a DICOM series to project your own volume instead of the example phantom.

Gamma camera — live projection

θ = 0°

drag detector = rotate gantry
drag background = orbit view · scroll = zoom

Couldn’t load Three.js from the CDN.

The 3D view needs an internet connection.
The projection and sinogram panels still work with the slider.

Controls

Show projection rays

Angles acquired: 0 / ?

Object — source of the projections

Example phantom (analytic)

Select all slice files of one uncompressed series (or a multi-frame file). Compressed transfer syntaxes (JPEG/JPEG2000) aren’t decoded here.

Sinograms — raw vs ramp-filtered (one row per angle)

raw

ramp filtered

← detector position s →↓ angle 0–360°

At each gantry angle the parallel-hole collimator records line integrals of the activity — an ideal parallel projection (attenuation and scatter ignored). Stacking the central-slice profile from every angle builds the sinogram: each hot spot traces a sinusoid. The ramp filter is the pre-weighting step of filtered backprojection; it boosts high spatial frequencies to cancel the 1/r blur, which is why the filtered sinogram looks edge-enhanced with dark overshoot lobes. Switch to the Reconstruct tab to invert this data. Inspired by Adam Kesner’s animated-GIF explanations.

simple backprojection (raw rows)

filtered backprojection (ramp-filtered rows)

true activity (slice)

θ = 0°

Controls

Sinogram rows used: 0 / ?

Measured sinograms — rows light up as they are used

raw

ramp filtered

← detector position s →↓ angle 0–360°

Current row, backprojected — one angle’s contribution

raw smear

filtered smear

Backprojection runs the acquisition in reverse: each sinogram row is smeared back across the image along the direction it was measured. Summing raw smears piles up a 1/r haze — simple backprojection stays blurry no matter how many angles are added. Ramp-filtering each row first adds negative side-lobes (blue in the filtered smear) that cancel the haze, so filtered backprojection converges to the true slice — already recognizable after ~180°. The object (example phantom or loaded DICOM volume) is shared with the acquisition tab.