DIY Photoacoustic Imaging Phantom

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DIY Photoacoustic Imaging Phantom

ISEF Category: Biomedical Engineering

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Subcategory: Biomedical Sensors and Imaging  ·  Difficulty: Advanced  ·  Setup: Home Setup  ·  Time: 1 to 2 Months

The Hook

Photoacoustic imaging uses pulses of light to make tissue ring like a bell, then listens with an ultrasound transducer. Real clinical systems cost six figures. A laser pointer, a piezo disc, and a Python script demonstrate the same physics on a gelatin phantom. You can resolve ink-line vessels you embedded yourself.

What Is It?

Photoacoustic imaging works because light absorbed by tissue causes tiny thermal expansion. That expansion makes a sound. A pulsed laser and a microphone or piezo sensor capture the resulting acoustic wave.

A gelatin-graphite phantom mimics tissue absorption. Ink lines drawn through the phantom act as blood vessels. The laser pulse heats them more than the surroundings.

Delay-and-sum beamforming is a basic image-reconstruction method. By moving the piezo across the phantom and recording signals, you can reconstruct where the absorbers are. The result demonstrates a teachable, real photoacoustic pipeline.

Why This Is a Good Topic

Photoacoustic imaging is an active research field and the educational demo is rare at ISEF. You will learn pulsed-light safety, beamforming, and reconstruction algorithms.

Research Questions

  • How does laser pulse width change signal amplitude?
  • What is the effect of phantom absorber depth on reconstruction quality?
  • Does delay-and-sum beat a simple time-of-flight method?
  • To what extent does piezo bandwidth limit resolution?
  • Which ink concentration maximizes signal-to-noise ratio?
  • How does scan step size affect resolution?
  • What is the effect of sound speed assumptions on reconstruction errors?

Basic Materials

  • Pulsed laser pointer or laser diode with safety housing (low-power, class 2).
  • Piezo disc and amplifier.
  • Gelatin and graphite for phantom.
  • Ink and fine wire for vessel mimics.
  • Microcontroller for synchronization.
  • Linear stage.
  • Laser-safety eyewear.

Advanced Materials

  • Q-switched nanosecond laser (with strict safety training).
  • Calibrated ultrasound transducer.
  • Optical detector for triggering.
  • Optics lab access.

Software & Tools

  • Python (NumPy and SciPy): Implements delay-and-sum beamforming.
  • OpenCV: Visualizes reconstructed images.
  • Audacity or Sigrok: Captures piezo waveforms.
  • Matplotlib: Plots resolution and SNR.

Experiment Steps

  1. Document laser-safety class and wear eyewear.
  2. Cast a phantom with known ink-line geometry.
  3. Lock laser-pulse timing and scan step size.
  4. Capture waveforms at each scan position.
  5. Run delay-and-sum reconstruction.
  6. Compare resolution against the known geometry.

Common Pitfalls

  • Skipping laser-safety review.
  • Mixing phantom batches with different graphite.
  • Using a piezo whose bandwidth is below the photoacoustic signal.
  • Assuming sound speed without measuring it in the phantom.
  • Reporting one scan as a result.

What Makes This Competitive

A competitive entry quantifies spatial resolution against a known ink-line geometry, runs multiple absorber positions, calibrates the laser pulse, and documents safety (laser class, eye protection). Comparing reconstruction quality across beamforming variants strengthens the engineering story.

Project Variations

  • Replace ink with hemoglobin-mimic dye for vessel oxygen-saturation imaging.
  • Add a circular scan for 2D reconstruction.
  • Compare delay-and-sum to a back-projection algorithm.

Learn More

  • PubMed: Search photoacoustic imaging tutorial review.
  • NIH PubMed Central: Open-access photoacoustic phantom papers.
  • Open-source k-Wave toolbox documentation.
  • American National Standards Institute laser-safety standards Z136 overview pages.
  • MIT OpenCourseWare: Course 6.555 Biomedical Signal and Image Processing.
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