G2500 1kg

Blood vessel phantoms were composed of silicon tubing (11–189-15H, Fisher Scientific) with an inner and outer diameter of 1.98 mm and 3.18 mm, respectively. Phantom skin tissue consisted of an 18% gelatin concentration derived from porcine skin (G2500–1KG, Sigma Life Science). The gelatin solution underwent four heating cycles (5 seconds each) in a 1200 W microwave, and was then placed in a 10 × 20 × 1.5 cm 3D-printed box, containing the silicon tubing in order to solidify. The phantom vessels were placed at a depth of 2 mm, measured from the gelatin surface to the outer wall of the tubing. More details associated with the fabrication of tissue phantoms can be found in Chen et al.^{30 (link)}. The BMF solution was pumped through the blood vessel phantoms via a peristaltic pump (12 V, #1150, Adafruit Industries) at a rate of 35 ml/min, approximating the resting venous flow rate of healthy adults.

The intralipid–gelatin phantom was made from intralipid (Intralipid 20%, Fresenius Kabi, Sweden), porcine skin gelatin (10% by weight, no. G2500-1kG, gel strength 300, Sigma-Aldrich, USA) and de-ionized water⁵¹ with a lipid concentration of 1.5 g ml⁻¹. The reduced scattering coefficient μ_S’ was measured by a home-built oblique incidence reflectometer^{52 (link)} to be 9.8 cm⁻¹.
Acrylic spacers with a thickness of 1.5 mm were sandwiched between two acrylic sheets to accurately control the thickness of the intralipid–gelatin phantom to be 1.5 mm (equivalent to $1.5l_{\mathrm{t}}^{\prime }$ ). The clear gelatin-gel layer was made from porcine skin gelatin (10% by weight) and de-ionized water. The optical absorptive target (3.9 mm 1.3 × mm 20.0 × mm along the x, y and z directions) was made from black ink, gelatin and distilled water. The absorption coefficient of the target was 0.80 cm⁻¹, as measured by a spectrophotometer (Cary Eclipse, Varian, USA). The diffuser (DG20-120, Thorlabs, USA) was embedded inside the gelatin gel to position it closer to the absorptive target (distance = 8.0 mm) and the intralipid–gelatin layer (distance = 22.1 mm) without blocking the ultrasonic waves.