A custom-built PET phantom design for quantitative imaging of printed distributions

Abstract

This note presents a practical approach to a custom-made design of PET phantoms enabling the use of digital radioactive distributions with high quantitative accuracy and spatial resolution. The phantom design allows planar sources of any radioactivity distribution to be imaged in transaxial and axial (sagittal or coronal) planes. Although the design presented here is specially adapted to the high-resolution research tomograph (HRRT), the presented methods can be adapted to almost any PET scanner. Although the presented phantom design has many advantages, a number of practical issues had to be overcome such as positioning of the printed source, calibration, uniformity and reproducibility of printing. A well counter (WC) was used in the calibration procedure to find the nonlinear relationship between digital voxel intensities and the actual measured radioactive concentrations. Repeated printing together with WC measurements and computed radiography (CR) using phosphor imaging plates (IP) were used to evaluate the reproducibility and uniformity of such printing. Results show satisfactory printing uniformity and reproducibility; however, calibration is dependent on the printing mode and the physical state of the cartridge. As a demonstration of the utility of using printed phantoms, the image resolution and quantitative accuracy of reconstructed HRRT images are assessed. There is very good quantitative agreement in the calibration procedure between HRRT, CR and WC measurements. However, the high resolution of CR and its quantitative accuracy supported by WC measurements made it possible to show the degraded resolution of HRRT brain images caused by the partial-volume effect and the limits of iterative image reconstruction.

Technical Note: Characterization of custom 3D printed multimodality imaging phantoms

“…of part dimension. The plastic used in our 3D printer was VisiJet M3 Crystal with a density of 1.02 g/cm 3 (for other material properties, see Ref. 7).…”

“…Several types of imaging phantoms exist, including plastic or glass cavities, suspensions of gel 1 or wax, 2 and ink-jet printed 2D surfaces. 3 Commercially available phantoms can be expensive and difficult to customize, while making a phantom with a precise customized geometry may be very difficult and time consuming. Three dimensional (3D) printers offer an attractive alternative to traditional phantom construction techniques.…”

Full field spatially-variant image-based resolution modelling reconstruction for the HRRT

“…The PSF was measured and characterised in detail across the entire FOV of the HRRT, using a printed point source array [7,16] and a custom-made perspex phantom [17]. Standard black ink was mixed with approximately 1 GBq of fluorine-18 and was injected into a modified cartridge.…”

Isotope dependent system matrices for high resolution PET imaging

“…The mean positron range for Carbon-II and Fluorine-IS is l.266 mm and 0.660 mm, respectively, with a theoretical difference of 0.606 mm between them [5]. Radioactive printing has been used previously to measure the spatial resolution properties of PET scanners and such a technique can provide fast, uniform and reproducible sources of arbitrary 2-dimensional activity distributions [4,6,7]. In this work, an Inkjet printer was used to print an array of 11 x 15 (axially x radially) radioactive point sources, 1 mm in diameter, with a I.S5 cm and 1.95 cm radial and axial sampling distance respectively.…”

“…The array was Radial distance (cm) placed horizontally in the HRRT FOY, using a Perspex phantom to facilitate accurate positioning and provide annihilating material for the positrons, covering almost the entire radial (-12.95 .. + 12.95 cm) and axial (-9.75 ... + 9.75 cm) FOY. The phantom was made out of 2 Perspex endplates held by 4 Perspex rods, with axial and transverse dimensions equal to the HRRT's bore, ensuring a tight fit during positioning [7]. The point-source array was scanned in list mode format for 60 minutes using Carbon-II (�65 million prompts) and for 20 minutes using Fluorine-IS (�I 00 million prompts), followed by a 6 minute transmission scan for attenuation correction.…”