Pertechnetate

Phantom measurements included dynamic imaging of the flow of a radiotracer bolus through the LVC and myocardial segments over time. Figure 3b presents an overview of the experimental setup during performance testing with a clinical cadmium-zinc-telluride SPECT system (D-SPECT, Spectrum Dynamics, Caesarea, Israel). The TMP and thorax phantom were positioned in the scanner’s field of view in a standard way. All flow circuit variables were set prior to dynamic MPI acquisition and were kept the same for the entire scanning period. The clinical dynamic MPI acquisition protocol consisted of two 6 min dynamic scans, namely a rest scan followed by a stress scan, respectively. The phantom cannot distinguish between these patient-related physiological states, though the additional scan can be used for another purpose. During the rest scan, no radiotracer was administered. This baseline scan was solely used for background subtraction of previously trapped radiotracer. The subsequent dynamic stress scan started just before injection of the radiotracer bolus. 1.5 mL of 500 MBq ^99mTc-pertechnetate solution was injected by a clinical contrast injector (Mark V Provis, Medrad, Warrendale, USA) at 1.0 mL/s, followed by a 40-mL saline flush.Fig. 3

Fluid circuit diagram of the Twente Myocardial Perfusion (TMP) phantom setup (top) and subsequent experimental setup during performance testing (bottom). The numbers represent the following components: 1. the myocardial perfusion (and thorax) phantom, 2. its accompanying fluid circuit, 3. in-house built hard- and software for pump steering and sensor readout, 4. dynamic SPECT scanner and 5. the contrast injector

After scanning, the orientation of the imaged heart contours was manually adjusted using vendor software. We applied the same rotation angles [i.e., 0° along the sagittal axis (SA) and 90° along the vertical long axis (VLA)] for all scans since the phantom was positioned under the scanner in a standard way. The list-mode image data was re-binned into 32 frames consisting of 21 frames of 3 s, 4 frames of 9, 15, 21 and 27 s, and 7 frames of 30 s. An ordered subset expectation maximization technique was used for reconstruction of the dynamic image acquisitions with 4 iterations and 32 subsets [19 ]. Detailed information on the clinical workflow with a D-SPECT scanner can be found in published studies [20 (link), 21 (link)].

Sodium ^[99mTc]pertechnetate (Na[^99mTc]TcO₄) was obtained from a ⁹⁹Mo/^99mTc generator (Tekcis, Curium Pharma Spain S.A. Madrid, Spain). All other chemicals and solvents used were purchased from Merck (Madrid, Spain), unless otherwise specified in the text. The ultrapure water (18.2 MΩ/cm) used in the experiments was produced in an ELGA Purelab Flex 2 (High Wycombe, UK).

The niosomes
were radiolabeled with [^99mTc]Tc using different amounts
of stannous chloride (10, 25, 50, 100, 500, and 1000 μg mL^–1, in distilled water), which was a reducing agent.^{10 (link),22 (link)} [^99mTc]-pertechnetate solution ([^99mTc]NaTcO₄) was eluted from the [⁹⁹Mo]Mo/[^99mTc]Tc
generator using 0.9% w/v NaCl (SF) solution. Briefly, 0.1 mL of [^99mTc]Tc (37 MBq mL^–1, Atomlab 100 Dose Calibrator,
Biodex Medical Systems) was mixed with stannous chloride solution.
To this composition, niosomal suspension (1 mL) was added, vortexed
for 1 min, and incubated for 15 min. The labeling efficiencies of
niosome formulations were assessed using both RTLC and R-UPLC.