Tiffinee Swanson

Adsorption of 99mTc-Sestamibi onto Plastic Syringes: Evaluation of Factors Affecting the Degree of Adsorption and Their Impact on Clinical Studies

The purpose of this study was to document the extent of adhesion of 99mTc-sestamibi to syringes in patient procedures, determine factors that influence the degree of adhesion, and evaluate alternatives to our current practice that would either result in a more reproducible degree of adhesion or, ideally, eliminate adhesion. Methods: The extent of adhesion was documented in 216 patient procedures and evaluated in detail in an additional 73 patient procedures. We evaluated the nature of the adhesion and its possible causes, including the location of adhesion in injection sets, the effect of syringe type, and the effect of prerinsing of syringes with various solutions of nonradiolabeled sestamibi and 99mTc-sestamibi. The extent of adhesion was reevaluated in 50 procedures performed using the syringe type that demonstrated the lowest adhesion rate. Results: The degree of adhesion of 99mTc-sestamibi to the injection set was found to be 20.1% ± 8.0%, with a range (10th–90th percentiles) of 9%–31%. The primary cause of adhesion appeared to be the lubricant used inside the syringe barrel. Evaluation of 6 different syringe types identified a brand with a lower adhesion rate. Reevaluation in patient procedures using this brand showed a 5.2% ± 2.5% degree of adhesion, with a range (10th–90th percentiles) of 2.5%–7.7%. Conclusion: Selection of the appropriate type of syringe can significantly reduce the magnitude and variability of residual 99mTc-sestamibi activity. With more reproducible residual activities, we have been able to achieve an approximately 20% reduction in the dispensed dose of 99mTc-sestamibi used in clinical procedures and a more consistent injected dose with less interpatient variation. The frequent changes in syringe design by manufacturers require that a quality control program for monitoring of residual activity be incorporated into clinical practice. This program has allowed us to maintain image quality and achieve more consistent injected patient doses in clinical procedures that use 99mTc-sestamibi.

Factors Influencing the Uptake of 99mTc-Sestamibi in Breast Tissue on Molecular Breast Imaging

The purpose of this study was to evaluate the impact of changes to a patient’s prandial status, metabolic status (rest vs. exercise), and peripheral blood flow (via caffeine or warming) on the uptake of 99mTc-sestamibi in breast tissue. Methods: A total of 154 subjects participated in 1 of 4 study groups that evaluated the effects of 4 types of intervention on the uptake of 99mTc-sestamibi in breast tissue (effect of fasting, light exercise, caffeine, and peripheral warming). Molecular breast imaging was performed before and after each intervention. Count density was assessed in counts/cm2/MBq from the mediolateral oblique view in all studies. Results: Uptake of 99mTc-sestamibi in breast tissue increased by approximately 25% from 6.6 counts/cm2/MBq in the fed state to 8.3 counts/cm2/MBq with fasting. Peripheral warming also resulted in an approximately 20% increase in count density from 9.1 to 10.9 counts/cm2/MBq. Conversely, exercise caused a 35% drop in count density relative to the resting state. Uptake did not seem to be influenced by caffeine and did not correlate with a patient’s height, weight, or breast thickness. There was only a weak correlation between breast activity and body surface area. Conclusion: The combined effects of fasting and warming resulted in an approximately 50% increased uptake of 99mTc-sestamibi in breast tissue relative to that observed in a reference group to whom no preparatory instructions had been given. Optimal patient preparation before administration of 99mTc-sestamibi should permit a corresponding reduction in either acquisition time or required dose of 99mTc-sestamibi.

Best Practices in Molecular Breast Imaging: A Guide for Technologists

Molecular breast imaging (MBI) technologists must have a combination of both nuclear medicine skills and mammographic positioning skills. Currently, no formal programs offer this type of hybrid technologist training. The purpose of this perspective is to provide a best-practices guide for technologists performing MBI. Familiarity with best practices may aid in obtaining high-quality MBI examinations by decreasing the likelihood of image artifacts, positioning problems, and other factors that contribute to false-negative or false-positive findings.

Guidelines for Quality Control Testing of Molecular Breast Imaging Systems

Molecular breast imaging (MBI) is a nuclear medicine test that uses dedicated γ-cameras designed for imaging of the breast. Despite growing adoption of MBI, there is currently a lack of guidance on appropriate quality control procedures for MBI systems. Tests designed for conventional γ-cameras either do not apply or must be modified for dedicated detectors. Our objective was to provide practical guidance for physics testing of MBI systems by adapting existing quality control procedures for conventional systems. Methods: Quality control tests designed for conventional γ-cameras were attempted on a dedicated MBI system and then modified as necessary to accommodate the pixelated detector, limited space between dual-detector heads, and inability to fully rotate the detector gantry. Results: MBI systems were found to warrant quality control testing of uniformity, spatial resolution, count sensitivity, energy resolution, and lesion contrast. The modified procedures and special considerations needed for these tests were investigated and described. Physics tests of intrinsic uniformity, count rate parameters, and overall system performance for SPECT did not apply to dedicated MBI systems. Conclusion: Routine physics testing of dedicated MBI equipment is important for verifying system specifications and monitoring changes in performance. As adoption of MBI grows, routine testing may be required for obtaining and maintaining accreditation from regulatory bodies.

Molecular Breast Imaging: Administered Activity Does Not Require Adjustment Based on Patient Size

At our institution, molecular breast imaging (MBI) is performed with 300 MBq of 99mTc-sestamibi for all patients. For some nuclear medicine procedures, administered activity or imaging time is increased for patients of larger size to obtain adequate counts. Our objective was to assess whether uptake of 99mTc-sestamibi in the breast is influenced by patient size. Methods: Records from patients who underwent a clinical MBI examination between July and November 2016 were reviewed. Those in whom our standard injection and preparation techniques were followed were included in the analysis. Patients were injected with approximately 300 MBq of 99mTc-sestamibi. Residual activity was measured to allow calculation of exact administered activity for each patient. Breast images were acquired at 10 min/view using a dual-head cadmium zinc telluride–based γ-camera. Breast thickness was measured as the distance between the 2 detectors. Patient height, weight, body surface area, and body mass index were obtained from records. Lean body mass with the James equation (LBMJames) and Janmahasatian correction (LBMJanma) was calculated. Count density in the breast tissue was measured by drawing a region of interest around the central breast tissue of the right breast mediolateral-oblique view of the lower detector. Count density was expressed as cts/cm2/MBq of administered activity. Spearman correlation coefficient (rs) was calculated. Results: A total of 200 patients were analyzed. No dose infiltration was suspected at any injection. Average administered activity was 292 MBq (SD, 13.8 MBq; range, 247–326 MBq). Average count density was 7.2 cts/cm2/MBq (SD, 2.7 cts/cm2/MBq; range, 3.1–17.8 cts/cm2/MBq). MBI count density was weakly negatively correlated with height (rs = −0.18; P = 0.01), weight (rs = −0.23; p = <0.001), body mass index (rs = −0.16; P = 0.02), body surface area (rs = −0.22; P = 0.002), LBMJames (rs = −0.23; P = 0.001), and LBMJanma (rs = −0.23; P = 0.001). No correlation was observed between count density and breast thickness (rs = 0.06; P = 0.37). Conclusion: Our results suggest a lack of relationship between uptake of 99mTc-sestamibi in breast tissue and body size or compressed breast thickness. Altering from the standard 300 MBq of administered activity for larger patients is likely unnecessary.

Quantitative background parenchymal uptake on molecular breast imaging and breast cancer risk: a case-control study

BackgroundBackground parenchymal uptake (BPU), which refers to the level of Tc-99m sestamibi uptake within normal fibroglandular tissue on molecular breast imaging (MBI), has been identified as a breast cancer risk factor, independent of mammographic density. Prior analyses have used subjective categories to describe BPU. We evaluate a new quantitative method for assessing BPU by testing its reproducibility, comparing quantitative results with previously established subjective BPU categories, and determining the association of quantitative BPU with breast cancer risk.MethodsTwo nonradiologist operators independently performed region-of-interest analysis on MBI images viewed in conjunction with corresponding digital mammograms. Quantitative BPU was defined as a unitless ratio of the average pixel intensity (counts/pixel) within the fibroglandular tissue versus the average pixel intensity in fat. Operator agreement and the correlation of quantitative BPU measures with subjective BPU categories assessed by expert radiologists were determined. Percent density on mammograms was estimated using Cumulus. The association of quantitative BPU with breast cancer (per one unit BPU) was examined within an established case-control study of 62 incident breast cancer cases and 177 matched controls.ResultsQuantitative BPU ranged from 0.4 to 3.2 across all subjects and was on average higher in cases compared to controls (1.4 versus 1.2, p < 0.007 for both operators). Quantitative BPU was strongly correlated with subjective BPU categories (Spearman’s r = 0.59 to 0.69, p < 0.0001, for each paired combination of two operators and two radiologists). Interoperator and intraoperator agreement in the quantitative BPU measure, assessed by intraclass correlation, was 0.92 and 0.98, respectively. Quantitative BPU measures showed either no correlation or weak negative correlation with mammographic percent density. In a model adjusted for body mass index and percent density, higher quantitative BPU was associated with increased risk of breast cancer for both operators (OR = 4.0, 95% confidence interval (CI) 1.6–10.1, and 2.4, 95% CI 1.2–4.7).ConclusionQuantitative measurement of BPU, defined as the ratio of average counts in fibroglandular tissue relative to that in fat, can be reliably performed by nonradiologist operators with a simple region-of-interest analysis tool. Similar to results obtained with subjective BPU categories, quantitative BPU is a functional imaging biomarker of breast cancer risk, independent of mammographic density and hormonal factors.

WE-AB-204-10: Evaluation of a Novel Dedicated Breast PET System (Mammi-PET)

Purpose: To evaluate the performance characteristics of a novel dedicated breast PET system (Mammi-PET, Oncovision). The system has 2 detector rings giving axial/transaxial field of view of 8/17 cm. Each ring consists of 12 monolithic LYSO modules coupled to PSPMTs. Methods: Uniformity, sensitivity, energy and spatial resolution were measured according to NEMA standards. Count rate performance was investigated using a source of F-18 (1384uCi) decayed over 5 half-lives. A prototype PET phantom was imaged for 20 min to evaluate image quality, recovery coefficients and partial volume effects. Under an IRB-approved protocol, 11 patients who just underwent whole body PET/CT exams were imaged prone with the breast pendulant at 5–10 minutes/breast. Image quality was assessed with and without scatter/attenuation correction and using different reconstruction algorithms. Results: Integral/differential uniformity were 9.8%/6.0% respectively. System sensitivity was 2.3% on axis, 2.2% and 2.8% at 3.8 cm and 7.8 cm off-axis. Mean energy resolution of all modules was 23.3%. Spatial resolution (FWHM) was 1.82 mm and 2.90 mm on axis and 5.8 cm off axis. Three cylinders (14 mm diameter) in the PET phantom were filled with activity concentration ratios of 4:1, 3:1, and 2:1 relative to the background. Measured cylinder to background ratios were 2.6, 1.8 and 1.5 (without corrections) and 3.6, 2.3 and 1.5 (with attenuation/scatter correction). Five cylinders (14, 10, 6, 4 and 2 mm diameter) each with an activity ratio of 4:1 were measured and showed recovery coefficients of 1, 0.66, 0.45, 0.18 and 0.18 (without corrections), and 1, 0.53, 0.30, 0.13 and 0 (with attenuation/scatter correction). Optimal phantom image quality was obtained with 3D MLEM algorithm, >20 iterations and without attenuation/scatter correction. Conclusion: The MAMMI system demonstrated good performance characteristics. Further work is needed to determine the optimal reconstruction parameters for qualitative and quantitative applications.