Dose Reduction in Molecular Breast Imaging With a New Image-Processing Algorithm.

OBJECTIVE. The purpose of this study was to determine whether application of a proprietary image-processing algorithm would allow a reduction in the necessary administered activity for molecular breast imaging (MBI) examinations. MATERIALS AND METHODS. Images from standard-dose MBI examinations (300 MBq 99mTc-sestamibi) of 50 subjects were analyzed. The images were acquired in dynamic mode and showed at least one breast lesion. Half-dose MBI examinations were simulated by summing one-half of the dynamic frames and were processed with the algorithm under study in both a default and a preferred filter mode. Two breast radiologists independently completed a set of two-alternative forced-choice tasks to compare lesion conspicuity on standard-dose images, half-dose images, and the algorithm-processed half-dose images in both modes. RESULTS. Relative to the standard-dose images, the half-dose images were preferred in 4, the default-filtered half-dose images in 50, and preferred-filtered half-dose images in 76 of 100 readings. Compared with standard-dose images, in terms of lesion conspicuity, the half-dose images were rated better in 2, equivalent in 6, and poorer in 92 of 100 readings. The default-filtered half-dose images were rated better, equivalent, or poorer in 13, 73, and 14 of 100 readings. The preferred-filtered half-dose images were rated as better, equivalent, or poorer in 55, 34, and 11 of 100 readings. CONCLUSION. Compared with that on standard-dose images, lesion conspicuity on images obtained with the algorithm and acquired at one-half the standard dose was equivalent or better without compromise of image quality. The algorithm can also be used to decrease imaging time with a resulting increase in patient comfort and throughput.

Radiolocalization of atypical lesions for intraoperative identification: technical factors, localization quality, success rates, patient safety, and spectrum of applications.

BACKGROUND: To retrospectively analyze perilesional technetium Tc-99m MAA injection for intraoperative localization of atypical soft-tissue and bone lesions within a single tertiary referral center in order to determine technique, safety, and clinical utility of these procedures. METHODS: An IRB compliant, retrospective electronic chart review (2010-2017) exploring surgical excision of atypical (non-pulmonary, non-breast, non-sentinel node) lesions guided by Tc-99m MAA perilesional injection. Patient demographics, lesion location, lesion size, radiotracer injection technique, radiotracer injection complications, scintigraphy technique, scintigraphic quality, intraoperative time, lesion identification in surgery, and pathological diagnoses were recorded. RESULTS: Twenty-two atypical radiolocalization exams were identified. Lesion sites included rib (7), lymph node (4), abdominal wall (3), mesenteric (3), gallbladder fossa (1), retroperitoneum (1), parietal pleura (1), anterior mediastinum (1), and iliac bone (1). Average lesion size was 14 mm (range 5-23 mm). Eighteen (82%) radiotracer injections used computed tomography guidance and 4 (18%) used ultrasound guidance. The mean activity of Tc-99m MAA administered was 11.8 MBq (0.32 mCi). A 22-gauge needle was most often used for perilesional injection. No injection complications were reported. The lesions were identified with a hand-held gamma probe during surgery in 100% of cases. Of the samples sent to pathology, 100% were identified and given a diagnosis. CONCLUSION: Radiolocalization of atypical lesions may be a valuable technique, guiding minimally invasive surgical removal of lesions that would otherwise be difficult to identify intraoperatively such as non-palpable rib, central mesenteric nodal, and abdominal wall lesions.

Patient Acceptance of Half-dose Vs. Half-time Molecular Breast Imaging.

OBJECTIVE: A number of strategies have been implemented at our institution to allow reductions in the administered dose or imaging time for molecular breast imaging (MBI). In this work, we examine patient opinions of whether dose reduction or time reduction is preferred. METHODS: Sixty female volunteers were randomized to undergo MBI at either half-dose (150 MBq Tc-99m sestamibi; images acquired for 10 minutes per view) or half-time (300 MBq Tc-99m sestamibi; images acquired for 5 minutes per view). A survey was then performed to assess patient comfort and examination preferences. Survey responses were compared between groups using Fisher's exact test. RESULTS: No differences were observed between groups regarding opinions of radiation dose, duration of examination, examination comfort, and willingness to undergo MBI in the future. Of those who responded, most women (39/55 [70%]) indicated a preference for the examination type they underwent, either half-dose or half-time MBI, rather than the other protocol. CONCLUSIONS: Survey findings support that MBI, whether performed at half-time or half-dose, is well accepted by patients.

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.

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

BACKGROUND: Background 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. METHODS: Two 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. RESULTS: Quantitative 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). CONCLUSION: Quantitative 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.

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.

Improved visualization of breast tissue on a dedicated breast PET system through ergonomic redesign of the imaging table.

BACKGROUND: Breast lesions closer than 2 cm to the chest wall are difficult to position in the field of view of dedicated breast PET (db-PET) systems. This inability to detect such lesions is a significant limitation of these systems. The primary objective of this study was to determine if modifications to the design of the imaging table and detector used for a db-PET system would enable improved visualization of breast tissue close to the chest wall. All studies were performed on a commercially available db-PET system (Mammi-PET). A central square section of the imaging table, containing the standard 180-mm circular aperture, was modified such that it could be removed and replaced by thinner sections with a larger aperture. Additional changes were made to the cover plate of the detector array and the patient mattress. A total of 60 patients were studied. After administration of F-18 FDG, 30 patients were imaged with a 220-mm-diameter aperture and the standard aperture, and 30 patients with a 200-mm aperture and the standard aperture. On all scans, the length of breast tissue in the field of view was measured as the greatest extent of tissue from the nipple back to the posterior edge of the breast. Image quality and patient comfort were recorded. RESULTS: Averaged over both breasts, relative to the standard aperture, the increase in breast length was 12.5 + 7.7 mm with the 220-mm aperture, and 12.3 + 6.5 mm with the 200-mm aperture (p < 0.05 for both apertures). In ~ 5% of cases, the larger apertures resulted in some degradation in image quality due to closer proximity to cardiac/hepatic activity. In 10-20% of cases, movement of the breast tissue was observed as the detector ring was moved to scan the anterior region of the breast. The patient survey indicated no significant difference in the comfort level between the standard aperture and either of the prototype apertures. CONCLUSIONS: Modifications to the image table and system resulted in a significant gain in the volume of breast tissue that could be imaged on the db-PET system and should allow better visualization of lesions close to the chest wall.

Adsorption of 99mTc-sestamibi onto plastic syringes: evaluation of factors affecting the degree of adsorption and their impact on clinical studies.

UNLABELLED: The purpose of this study was to document the extent of adhesion of (99m)Tc-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 (99m)Tc-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 (99m)Tc-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 (99m)Tc-sestamibi activity. With more reproducible residual activities, we have been able to achieve an approximately 20% reduction in the dispensed dose of (99m)Tc-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 (99m)Tc-sestamibi.