Kidney dynamic SPECT acquisition on a CZT swiveling-detector ring digicam: an in vivo pilot research | BMC Medical Imaging

Animal

A 7-week-old (12 kg) feminine Belgian Landrace pig was used for the experiment. The research was licensed by the institutional ethics committee associated to experimentation on animals (ref. 2022/UCL/MD/052 authorised on the 4th of April 2023).

Anesthesia was carried out simply earlier than the beginning of picture acquisition and was induced through intramuscular injection of 6 mg/kg Tiletamine 50 mg/ml and Zolazepam 50 mg/ml (Virbac, Leuven, Belgium) and a pair of mg/kg Xylazine 2% (Bayer, Mechelen, Belgium) and maintained through the realization of the experiment by two intravenous injections of Zolazepam by a 18G intravenous catheter inserted in an ear vein simply after anesthesia induction.

Acquisitions

The dynamic SPECT was carried out on a Basic Electrical Starguide SPECT/CT (GE Healthcare, Haifa, Israel). This digicam advantages from 7.3 mm-thick CZT crystals geared up with Tungsten parallel-hole collimators. 4 sq. collimator holes (1.03 × 1.03mm²) are related to every CZT pixel (2.46 × 2.46mm²). The pig was put in in supine place on the digicam desk in order that its kidneys have been within the digicam FOV. The 30 min dynamic acquisition was began a number of seconds earlier than the injection of 77.7MBq of [^99mTc]Tc-MAG3 by a catheter inserted into the pig’s ear. The delay between the acquisition’s begin and the injection time was set to permit the system to place the detectors near the animal after the beginning command initiation. The detector swivel movement was set to scan the pig space in 5s. Uncooked knowledge have been saved into an inventory mode file. As the present software program model of the Starguide digicam doesn’t enable to carry out a CT scan in the identical workflow than the dynamic SPECT, we’ve carried out a static SPECT/CT instantly after the dynamic SPECT acquisition so as to get a CT for attenuation correction.

The following day, one other research of the kidneys of the identical pig was carried out as a planar dynamic acquisition on a Philips Brightview 2-head gamma digicam (Philips, Milpitas, CA). This digicam features a 0.95 cm-thick NaI crystal related to a LEHR parallel-hole collimator. The power window was set as 140.51 keV ± 10%. The 30 min dynamic planar acquisition was recorded, in a 64 × 64 pixels matrix, as 60 frames of 5s adopted by 150 frames of 10s. The temporal sampling was subsequently just like the one of many SPECT acquisition. The acquisition was began whereas injecting 77.7MBq of [^99mTc]Tc-MAG3.

For each acquisitions, the [^99mTc]Tc-MAG3 answer had a quantity of about 2 ml and was injected as a bolus, adopted by a flush of saline answer to rinse the tubing.

The pig was sedated earlier than every acquisition and the sedation was managed and adjusted through the acquisition to cut back any animal movement.

SPECT reconstructions

The checklist mode file of the dynamic SPECT acquisition was sorted to generate a set of projections for every of the 12 column detectors, by grouping the continual swivel angles in 2 levels bins, i.e., the manufacturing facility sampling for routine static SPECT acquisitions. The ensuing numbers of projections differ from detector to detector in response to the swivel vary wanted to cowl the pig space from every detector place. They have been equal to 55, 48, 36, 50, 68, 74, 71, 62, 32, 57, 55 and 58 for the 12 detectors in clock order, respectively. Native pixel dimension was used for the projections, i.e., 2.46 × 2.46 mm in a 16 × 112 matrix, akin to the 7 CZT modules (4 × 4cm²) of every column detector. The power window was set as 140.51 keV ± 10%. To guage the temporal sampling, the 30 min acquisition was cut up up as 360 frames of 5s (360 × 5s), 180 frames of 10s (180 × 10s), 120 frames of 15s (120 × 15s), 60 frames of 30s (60 × 30s) and 30 frames of 60s (30 × 60s). Every time-frame was then reconstructed utilizing a Most Probability Expectation Maximization (MLEM) algorithm. To investigate the convergence of the reconstruction algorithm, as much as 20 iterations have been carried out on the 60 × 30s reframing, which is much less impacted by Poisson noise within the projections. Reconstructions have been carried out with and with out CT-based attenuation correction to supply computed tomography attenuation corrected (CTAC) and non-attenuation corrected (NAC) photographs, respectively. The registration between the CT and the dynamic SPECT resulted from the desk positions saved within the Digital Imaging and COmmunications in Drugs (DICOM) header of each acquisitions, because the pig was not moved between the scans.

Knowledge evaluation

Areas of curiosity (ROI) have been manually drawn round each kidneys and the background on the planar photographs. Time-activity curves (TAC) have been generated by correcting the entire counts of every kidney ROI for background exercise.

For the SPECT photographs, ROIs have been manually drawn across the kidneys on the CT picture, then transferred to the registered dynamic SPECT photographs. To compensate for partial quantity results and restricted SPECT spatial decision, the CT ROIs should be prolonged on the SPECT picture. A comparability of the dynamic curve parameters was carried out for extensions of the ROIs from 0 cm as much as 2 cm in all instructions. Whole counts of every kidney ROI in NAC and CTAC photographs have been compiled into corresponding TACs. For example one of many benefits of dynamic SPECT over dynamic planar imaging, i.e., the chance to carry out regional evaluation of the organs, the kidney’s ROIs have been cut up in halves alongside the superior-inferior axis. These kidney’s halves have been then processed individually to generate TACs to be in comparison with the complete kidneys TACs.

Compartmental mannequin

To investigate the time-activity curves, we use an tailored 2-compartment kinetic mannequin. Within the 2-compartment mannequin, the exercise focus within the kidney ( {C}_{Ok}left(tright)) will be expressed as a bi-exponential operate

with the speed constants ( {ok}_{i}) and ( {ok}_{o})akin to the transfers from the blood to the kidney and from the kidney to the bladder, respectively.

As a result of the pig didn’t empty its bladder neither earlier than nor through the scans, and as no catheter was launched into the bladder to power its emptying, we can’t anticipate a continuing price of elimination of the MAG3 from the kidneys [9, 10]. The sedative injected to the animal might also influence the fixed price ( {ok}_{o}) [11]. To take these results into consideration within the mannequin, we introduce a time dependent price ( {Ok}_{o}left(tright)), and Eq. (1) turns into

Because the ( {Ok}_{o}left(tright)) operate is unknown and contains many animal- and scan-dependent parameters, we make the idea that it may be approximated by an exponential operate as

the place ( {ok}_{o}) and β are parameters. Expression (3) has the anticipated boundary habits: at t = 0, we discover the preliminary fixed price issue ( {ok}_{o})when the bladder is empty, and at bigger instances, ( {Ok}_{o}left(tright)) tends to zero as anticipated when the bladder is full. Equation (3) contains the traditional case of no bladder blocking when β is the same as zero.

Combining Eqs. (2) and (3), we get the tailored 2-compartment mannequin for the kidney operate

the place the parameters ( A), ( {ok}_{o}), β and ( {ok}_{i}) should be fitted to the measured time-activity curves.