Reduction in radiation dose in mercaptoacetyltriglycerine renography with enhanced planar processing.

PURPOSE: To determine the minimum dose of technetium 99m ((99m)Tc) mercaptoacetyltriglycerine (MAG3) needed to perform dynamic renal scintigraphy in the pediatric population without loss of diagnostic quality or accurate quantification of renal function and to investigate whether adaptive noise reduction could help further reduce the minimum dose required. MATERIALS AND METHODS: Approval for this retrospective study was obtained from the institutional review board, with waiver of informed consent. A retrospective review was conducted in 33 pediatric patients consecutively referred for a (99m)Tc-MAG3 study. In each patient, a 20-minute dynamic study was performed after administration of 7.4 MBq/kg. Binomial subsampling was used to simulate studies performed with 50%, 30%, 20%, and 10% of the administered dose. Four nuclear medicine physicians independently reviewed the original and subsampled images, with and without noise reduction, for image quality. Two observers independently performed a quantitative analysis of renal function. Subjective rater confidence was analyzed by using a logistic regression model, and the quantitative analysis was performed by using the paired Student t test. RESULTS: Reducing the administered dose to 30% did not substantially affect image quality, with or without noise reduction. When the dose was reduced to 20%, there was a slight but significant decrease (P = .0074) in image quality, which resolved with noise reduction. Reducing the dose to 10% caused a decrease in image quality (P = .0003) that was not corrected with noise reduction. However, the dose could be reduced to 10% without a substantial change in the quantitative evaluation of renal function independent of the application of noise reduction. CONCLUSION: Decreasing the dose of (99m)Tc-MAG3 from 7.4 to 2.2 MBq/kg did not compromise image quality. With noise reduction, the dose can be reduced to 1.5 MBq/kg without subjective loss in image quality. The quantitative evaluation of renal function was not substantially altered, even with a theoretical dose as low as 0.74 MBq/kg.

Quantitative accuracy of clinical 99mTc SPECT/CT using ordered-subset expectation maximization with 3-dimensional resolution recovery, attenuation, and scatter correction.

UNLABELLED: We present a calibration method of a clinical SPECT/CT device for quantitative (99m)Tc SPECT. We use a commercially available reconstruction package including ordered-subset expectation maximization (OSEM) with depth-dependent 3-dimensional resolution recovery (OSEM-3D), CT-based attenuation correction, and scatter correction. We validated the method in phantom studies and applied it to images from patients injected with (99m)Tc-diphosponate. METHODS: The following 3 steps were performed to derive absolute quantitative values from SPECT reconstructed images. In step 1, we used simulations to characterize the SPECT/CT system and derive emission recovery values for various imaging parameter settings. We simulated spheres of varying diameters and focused on the dependencies of activity estimation errors on structure size and position, pixel size, count density, and reconstruction parameters. In step 2, we cross-calibrated our clinical SPECT/CT system with the well counter using a large cylinder phantom. This step provided the mapping from image counts to kBq/mL. And in step 3, correction factors from steps 1 and 2 were applied to reconstructed images. We used a cylinder phantom with variable-sized spheres for verification of the method. For in vivo validation, SPECT/CT datasets from 16 patients undergoing (99m)Tc-diphosponate SPECT/CT examinations of the pelvis including the bladder were acquired. The radioactivity concentration in the patients' urine served as the gold standard. Mean quantitative accuracy and SEs were calculated. RESULTS: In the phantom experiments, the mean accuracy in quantifying radioactivity concentration in absolute terms was within 3.6% (SE, 8.0%), with a 95% confidence interval between -19.4% and +12.2%. In the patient studies, the mean accuracy was within 1.1% (SE, 8.4%), with a 95% confidence interval between -15.4% and +17.5%. CONCLUSION: Current commercially available SPECT/CT technology using OSEM-3D reconstruction, scatter correction, and CT-based attenuation correction allows quantification of (99m)Tc radioactivity concentration in absolute terms within 3.6% in phantoms and 1.1% in patients with a focus on the bladder. This opens up the opportunity of SPECT quantitation entering the routine clinical arena. Still, the imprecision caused by unavoidable measurement errors is a dominant factor for absolute quantitation in a clinical setup.

Improved lesion detection from spatially adaptive, minimally complex, Pixon reconstruction of planar scintigraphic images.

Pixon noise reduction was applied to 18 planar images, six each from 99mTc-methylene diphosphonate (99mTc-MDP), 67Ga citrate (67Ga), and (123)I-metaiodobenzylguanidine ((123)I-MIBG) studies. Pixon processing increased patient signal-to-noise ratio, 6.8-11.8 fold. Three specialists preferred processed images 44 of 54 times with good agreement (87%). Most (9/10, p<0.02) of the null and negative preferences were from (123)I-MIBG studies. Inter-rater association was shown for 1-4 scale rated artifact p<0.1, noise p<0.01 and lesion detection p<0.05. Pixon images had superior lesion detection ability, p<0.02, and noise levels, p<0.02 and no statistically significant change in artifacts.