Use the Imaging technique selector beside the PhysicsUK logo to switch between Ultrasound, X-ray imaging, CT (CAT scan), Gamma camera and PET. Measure echoes, reconstruct slices and follow gamma emission or positron annihilation into the signals that build an image. Each workspace has prepared investigations, a patient case and a What am I seeing? explanation. Use the compact evidence tabs or Compare to see images and graphs together.
What you can investigate
- Pulse travel and echo timing through independently editable tissue objects
- Acoustic impedance, reflection and coupling gel
- A-scan cursors and depth measurements
- B-scans built from acquired lines across the phantom
- Pulse length, frequency, resolution and attenuation
- Doppler flow, probe angle and recorded evidence
- X-ray tube production, attenuation and projection images linked to detector traces
- CT fan-beam views, acquired sinograms and reconstructed slices
- Gamma-camera collimation, scintillation, pulse signals and count images
- Positron emission, annihilation, PET coincidence timing and measured lines
- Physical, biological and effective half-life
How deep is the hidden boundary?
- Choose Find the hidden boundary and send a pulse. Follow its outward and return journey.
- Place cursor A on the transmit peak and cursor B on the returning echo. Calculate depth using the stated sound speed and half the round-trip time.
- Enter your depth, check the calculation and capture the reading. Reveal the structure, move a tissue boundary, and repeat.
Echo time includes travel to the boundary and back. In a uniform medium, depth = cΔt/2. A layered phantom uses each layer’s actual sound speed; the scanner’s assumed speed can therefore produce a different apparent depth.
Interpreting the model
One ultrasound pulse produces one B-scan column; the A-line beside it shows the same echoes. Sweep scan builds the section. Ultrasound uses synthetic acoustic materials and single reflections. X-ray and CT use NIST attenuation data for a 3D water/bone/air phantom and a monochromatic beam. Each CT sinogram row is an angle and each cell measures attenuation along one ray. Select a cell to follow that ray through the reconstructed slice; many intersecting measurements constrain the image pixels. CT step by step animates the projection, its row transfer and the successive reconstruction. Follow an object to see its curved track across measured rows; orange outlines are a revealed model guide, while cell brightness includes all materials on the ray. The reconstruction uses measured detector data only; zero-count rays are flagged and omitted. Scatter, beam hardening and detector blur are excluded. Gamma images accumulate accepted photons through real collimator channels; PET images accumulate measured coincidence lines. PET uses a declared 2D teaching model and unfiltered backprojection. Selected single-event replays are separate from timed radioactive counts.
Revision and practice