Image: Four differently sized 3D printed phantom kidneys (Photo courtesy of Johannes Tran-Gia).
A new study suggests that three dimensional (3D) printed kidney phantoms could help determine calibration constants in quantitative single-photon emission computed tomography/ computerized tomography (SPECT/CT) imaging.
Researchers at the University of Würzburg (Germany) created a set of four one-compartment kidney dosimetry phantoms and their spherical counterparts, with filling volumes ranging from 8 mL (for newborns) and 123 mL (for adults). The phantom designs were based on the outer kidney dimensions, as provided by medical internal radiation ddose (MIRD) guidelines. Based on the designs, the four refillable, waterproof, and chemically stable models were manufactured using fused deposition polylactide (PLA) modeling on a Conrad (Wernberg-Köblitz, Germany) Renkforce RF1000 FFF 3D printer.
The researchers then applied nuclide-dependent SPECT/CT calibration factors for technetium-99m (Tc-99m), lutetium-177 (Lu-177), and iodine-131 (I-131) to assess the phantoms accuracy when used in quantitative imaging for internal renal dosimetry. The results showed that for the largest phantom, the volumes of interest had to be enlarged by 1.2 mm for 99mTc, 2.5 mm for 177Lu, and 4.9 mm for 131 in all directions to obtain calibration factors comparable to reference. In decreasing phantom volumes, the difference between corresponding sphere–kidney pairs was small, at less than 1.1% for all volumes. The study was published on December 1, 2016, in The Journal of Nuclear Medicine.
“This research shows a way of producing inexpensive models of patient-specific organs/lesions for providing direct and patient-specific calibration constants. This is particularly important for imaging systems suffering from poor spatial resolution and ill-defined quantification, such as SPECT/CT,” said lead author Johannes Tran-Gia, PhD. “With comparably low costs and submillimeter resolution, 3D printing techniques hold the potential for manufacturing individualized anthropomorphic phantoms in many clinical applications in nuclear medicine.”
An imaging phantom is designed to respond in a similar manner to how human tissues and organs would act in order to evaluate, analyze, and tune performance of a specific imaging modality. Phantoms made for radiography may therefore hold various quantities of x-ray contrast agents with absorbing properties similar to normal tissue, so as to tune image contrast or modulate radiation exposure. For ultrasound, on the other hand, a phantom with similar rheological and ultrasound scattering properties to real tissue would be essential, but x-ray absorbing properties would not be needed.
University of Würzburg