Can99mTc-MDP-SPECT/CT Differentiate Loosening and Infection After Hip and Knee Replacements?

Background: Prosthetic loosening and infection are still common complications after joint replacement. Over the past few years, single-photon emission computed tomography-computed tomography (SPECT/CT) was widely used and showed unique value based on the combination of anatomic and metabolic information of foci. However, its performance in differentiating between prosthetic loosening and periprosthetic infection after joint replacement is still the focus of clinicians and deserves further investigation. Purpose: This retrospective study was aimed to determine whether bone scintigraphy combined with SPECT/CT still can differentiate prosthetic infection from loosening in patients after joint replacement. The differential efficacy in hip and knee prosthesis was also analyzed. Blood biomarkers for the diagnosis of periprosthetic infection were also evaluated. Patients and methods: Data sets of 74 prosthetic joints (including knees and hips), with suspected prosthetic loosening or infection between 2015 and 2021, were evaluated. Besides the results of nuclear imaging, X-ray images and serum biomarker were also recorded. Telephone follow-up and revision surgery after SPECT/CT were used as a gold standard. The sensitivity and accuracy of different imaging modalities were calculated by Chi-square test. The diagnostic efficacy of imaging methods and serum biomarkers were then analyzed by the area under curve (receiver operating characteristic curves, ROC) in SPSS 26. Results: In all, 47 joints (14 knees and 33 hips) were confirmed as aseptic loosening, while 25 joints (18 knees and 7 hips) were confirmed as infection. The sensitivity and accuracy of SPECT combined with SPECT/CT imaging were the highest (92.86% and 87.84%, respectively). The differential efficacy of bone scintigraphy combined with SPECT/CT imaging was also better than any other single imaging modality. In the analysis of involved prosthesis, prosthetic loosening occurred more in hip prosthesis and knee prosthesis was easily infected (P < 0.05). Finally, the sensitivity of ESR and CRP were 80% and 84%, respectively. Conclusions: Bone scintigraphy with hybrid SPECT/CT remains encouraging in differentiating prosthetic infection from loosening after joint replacement. The diagnostic efficacy of differentiation in hip prosthesis was better than knee. Serum biomarkers cannot be used alone to differentiate prosthetic infection from loosening.

Comparison of diagnostic efficacy between 99mTc-methylene diphosphate SPECT/CT and MRI for bone and joint infections: a multicenter retrospective analysis.

Objective: There is currently no non-invasive examination that can fully determine the diagnosis of osteomyelitis. SPECT/CT tomographic fusion imaging can provide both local metabolic activity and anatomical information to determine the condition and location. This study evaluates the diagnostic efficacy of 99mTc-MDP SPECT/CT in bone infections, compared to MRI. Methods: In this multicenter retrospective study, 363 patients with suspected bone and joint infections or osteomyelitis were included. Participants underwent 99mTc-MDP SPECT/CT and/or MRI examinations, supplemented by pathogenic bacterial cultures and histopathological analysis. Results: Only SPECT/CT was tested in 169 patients, and only MRI was used in 116. 78 people have implemented both inspections and have detailed information. The diagnostic sensitivity and specificity of SPECT/CT for infection were 96% and 92% respectively, with an accuracy of 96%. For MRI, these figures were 88%, 84%, and 87% respectively. Conclusion: This represents the largest global study to date evaluating osteomyelitis and bone infection diagnosis using 99mTc-MDP SPECT/CT tomographic fusion imaging. The findings indicate that 99mTc-MDP SPECT/CT fusion imaging offers superior diagnostic accuracy compared to MRI. This is particularly evident in cases involving metallic implants and chronic infections. 99mTc-MDP SPECT/CT fusion imaging emerges as a highly suitable non-invasive diagnostic modality, facilitating enhanced clinical follow-up and treatment.

Case report: Exploring the utility of whole-body bone scintigraphy for pediatric Langerhans cell histiocytosis: insights from clinical practice.

Purpose: This mini-review delves into the realm of Langerhans cell histiocytosis (LCH) in children, focusing on its skeletal involvement. By synthesizing pertinent literature, we sought to provide a comprehensive understanding of LCH's clinical and radiographic spectrum. Our study then demonstrates the diagnostic prowess of whole-body 99mTc-methyl diphosphonate (MDP) scintigraphy in LCH cases, underscoring its value in tandem with existing knowledge. Methods: Our approach involved an extensive literature review that contextualized LCH within the current medical landscape. Subsequently, we presented a case series featuring five pediatric instances of skeletal LCH, one accompanied by soft tissue infiltration. The principal aim was to illuminate the diagnostic and staging potential of whole-body 99mTc-MDP scintigraphy, augmenting existing insights. Results: Through meticulous literature synthesis, we highlighted pediatric LCH's protean clinical manifestations and radiological variability. Aligning with this spectrum, our case series underscored the role of 99mTc-MDP scintigraphy in diagnosing and staging LCH. Among the five pediatric cases, one demonstrated concurrent soft tissue involvement. This aligns with the multifaceted nature of LCH presentations. Conclusion: Pediatric LCH can present with a wide range of clinical and radiologic features. By amalgamating our cases with extant literature, we stress the necessity of a multimodal strategy. 99mTc-MDP scintigraphy emerged as an indispensable tool for accurate staging and soft tissue detection. Our findings collectively advocate for a holistic approach to managing LCH, ensuring informed therapeutic decisions for optimal patient outcomes.

Assessment of unilateral condylar hyperplasia with quantitative SPECT/CT.

Purpose: The current study aimedto assess condylar activityin patients with unilateral condylar hyperplasia (UCH) with quantitative SPECT/CT. Patients and methods: This retrospective study included patients with UCH who underwent quantitative SPECT/CT. SPECT analysis and quantification of SPECT/CT were performed, and the maximum count per pixel and SUVmax of either side of the condyles were calculated. Results: 39 patients were included in the analysisand classified into three subgroups according to the percentile differential right-left ratio: inactive group, left active (LA) group, and right active (RA) group. Totally, the SUVmax of the affected side is significantly higher than the unaffected side (active:5.93 ± 2.43 vs inactive:3.62 ± 1.76, P < 0.001), SUVmax-based ratios correlated well with the ratios based on maximum count (R = 0.944, P < 0.001). ROC analysis showed poorSUVmaxperformance in differentiation between theactive condyles and the inactive condyles due to the lower area under the curve (AUC) (0.588). In subgroup analysis, the affected side is significantly higher than the unaffected side in active groups with SUVmax, no significant difference was found between the active sides or the inactive sides of active groups. Interestingly, the SUVmax of the left side was statistically higher than that of the right sidein the inactive group (P = 0.01),while the left side of the right active group has significantlylower activitythan that in the inactive group, meanwhile,the right side showed no significant difference. Furthermore, each side showed no significant difference between the left active group and the inactive group. Conclusions: SUVmax is not an optimal measurement effectively used to evaluate active condyles. However, SUV ratios correlated well with the count ratios, and the left side of condyles showed a peculiar feature in condyle growth status reflected in radioactivity quantified with SPECT/CT, which needs further study to determine the role in the development of the UCH.

The 'Eye Mask Sign' in Fibrous Dysplasia on 99mTc-MDP Skeletal Scintigraphy and SPECT/CT.

Fibrous dysplasia (FD) is a fibro-osseous disorder that manifests with distinct or overlapping clinical patterns. FD may be monostotic or polyostotic and commonly associated with syndromes such as McCune-Albright syndrome and Mazabraud syndrome. We report a case of polyostotic FD with bilateral involvement of craniofacial bones in a distinct pattern and propose this characteristic appearance as the 'eye mask sign' on 99mTc-Methylene Diphosphonate (MDP) skeletal scintigraphy and SPECT/CT. Other unusual skeletal scintigraphic features noted in this case are also described (Figs. 1, 2, and 3).

Delayed epiphyseal closure in an adult with panhypopituitarism detected by 99mTc-MDP bone SPECT/CT.

We reported a 23-year-old male patient with panhypopituitarism who underwent two resections for craniopharyngioma and received postoperative hormone replacement therapy. The 99mTc-MDP bone scan revealed focal high uptake of radioactive nuclide in multiple large joints. The SPECT/CT demonstrated the focal high uptake in their metaphysis. Thus, delayed epiphyseal closure was considered.

Multiple uptake of 99mTc-MDP in chest due to breast implant rupture in a patient with lung adenocarcinoma.

A 57-year-old woman was diagnosed as lung adenocarcinoma. 99mTc-MDP bone scan showed multiple radioactivity concentrated lesions on bilateral chest wall, which were confirmed as calcification foci after breast implant rupture by SPECT/CT. SPECT/CT could be used for differential diagnosis of breast implant rupture and malignant lesions.

A case of accidental local pulmonary 99mTc-MDP uptake on bone SPECT/CT.

We report a case of accidental local 99mTc-MDP uptake in left lung on bone scan without pulmonary parenchymal abnormality on SPECT/CT. The abnormal uptake disappeared on repeated bone scan and SPECT/CT after 3 days. It is speculated that the high radioactivity focus is a microthrombus in pulmonary artery.

Prostatic bed calcification with MDP uptake: Easy to miss on planar images.

A 65 years old man with high-risk prostate adenocarcinoma underwent bone scintigraphy with 99mTc-methylene diphosphate (99mTc-MDP). The scan revealed a focus of radiotracer uptake in the left pubic region, which was suspicious for metastatic involvement. Additional imaging with single photon emission computed tomography (SPECT/CT) confined the uptake to be extra-osseous and contributed to the calcified zone in the prostate bed. Prostatic bed calcification with 99mTc-MDP uptake mimics metastasis and can be easily missed on planar images.

Detecting multiple lesions of lung cancer-caused metastasis with bone scans using a self-defined object detection model based on SSD framework.

Objective.To facilitate manual diagnosis of lung cancer-caused metastasis, in this work, we propose a deep learning-based method to automatically identify and locate the hotspots in a bone scan image which denote the lesions metastasized from lung cancer.Approach.An end-to-end metastasis lesion detection model is proposed by following the classical object detection framework single shot multibox object detector (SSD). The proposed model casts lesion detection problem into automatically learning the hierarchal representations of lesion features, locating the spatial position of lesion areas, and boxing the detected lesions.Main results.Experimental evaluation conducted on clinical data of retrospective bone scans shows the comparable performance with a mean score of 0.7911 for average precision. A comparative analysis between our network and others including SSD shows the feasibility of the proposed detection network on automatically detecting multiple lesions of metastasis lesions caused by lung cancer.Significance.The proposed method has the potential to be used as an auxiliary tool for improving the accuracy and efficiency of metastasis diagnosis routinely conducted by nuclear medicine physicians.

Specific pattern of bone scan as a result of unintentional-intraarterial injection into the ulnar artery.

Background: Bone scintigraphy with 99mTc labeled radiopharmaceuticals is a valuable method in nuclear medicine for assessing the bony structure. In clinical setting, bone scintigraphy is accomplished after the injection of 99mTc labeled diphosphonate complexes into a peripheral vein. Inadvertent intra-arterial injection on the antecubital region may cause a special form of artifacts leading to problems inaccurately interpreting these studies as functional images. Case Presentation: We present a 44-year-old man with history of chest wall pain for bone scintigraphy as part of a work-up for determining the pain source. The patient received an injection of 740MBq 99mTc-methylene diphosphonate (MDP) into a blood vessel at the right forearm. Two hours later, an increased uptake of activity was observed on the right forearm and ulnar half of the wrist-hand in the whole body and spot images. The scan findings were consistent with the anatomical and physiological expectations of the ulnar arterial perfusion range. This case displays that an incidental injection with a 99mTc labeled diphosphonate into the ulnar artery results in a hot ulnar half of the palm and ulnar-sided three digits, because these areas are directly exposed to radiopharmaceutical, therefore more radiopharmaceutical is deposited. Conclusion: It is important for the physician, and especially for the nuclear medicine technician, to know the specific appearance created in the bone scan due to such an event so that they do not make a diagnostic mistake.

Prospective study of Na[18F]F PET/CT for cancer staging in morbidly obese patients compared with [99mTc]Tc-MDP whole-body planar, SPECT and SPECT/CT.

PURPOSE: This prospective study aims to assess the diagnostic test characteristics of Na[18F]F PET/CT for the skeletal staging of cancer in morbidly obese patients compared with 99mTc-methylene diphosphonate (MDP), whole-body planar (WBS), SPECT, and SPECT/CT acquisitions. MATERIAL AND METHODS: One hundred seventeen obese patients (BMI 46.5 ± 6.1 kg/m2 and mean age, 59.0 years; range 32-89 years) with BMI > 40 kg/m2 were prospectively enrolled and underwent [99mTc]Tc-MDP WBS, SPECT, SPECT/CT, and Na[18F]F PET/CT within two weeks for the osseous staging of a malignancy. Images were assessed qualitatively using a 3-point scale. Patient and lesion-based diagnostic test characteristics were estimated using an optimistic and pessimistic dichotomization method. RESULTS: Bone metastases were confirmed in 44 patients. Patient-based optimistic diagnostic test characteristics were (sensitivity, specificity, overall accuracy): Na[18F]F PET/CT (95.5%, 95.9%, 95.7%), [99mTc]Tc-MDP WBS (52.3%, 71.2%, 64.1%), SPECT (61.4%, 80.8%, 73.5%) and SPECT/CT (65.9%, 91.8%, 82.1%). Lesion-based optimistic diagnostic test characteristics were: Na[18F]F PET/CT (97.7%, 97.9%, 97.7%), [99mTc]Tc-MDP WBS (39%, 67%, 48.9%), SPECT (52.9%, 93.6%, 67.3%) and SPECT/CT (65.9%, 91.8%, 82.1%). There was no significant difference in the specificity of Na[18F]F and SPECT/CT. All other pairwise comparisons were significant (p<.001). ROC curve analysis showed a high overall accuracy of Na[18F]F with significantly higher AUCs for Na[18F]F PET/CT compared to [99mTc]Tc-MDP WBS, SPECT, and SPECT/CT on both patient and lesion-based analysis (p<.001). Moreover, Na[18F]F PET/CT changed patient management in 38% of patients. CONCLUSIONS: Na[18F]F PET/CT may be the preferred imaging modality for skeletal staging in morbidly obese patients. The technique provides excellent diagnostic test characteristics superior to [99mTc]Tc-MDP bone scan (including SPECT/CT), impacts patient management, has an acceptable radiation exposure profile, and is well-tolerated. Further cost-effectiveness evaluations are warranted.

Application of 68Ga-citrate PET/CT for differentiating periprosthetic joint infection from aseptic loosening after joint replacement surgery.

AIMS: We aimed to evaluate the utility of 68Ga-citrate positron emission tomography (PET)/CT in the differentiation of periprosthetic joint infection (PJI) and aseptic loosening (AL), and compare it with 99mTc-methylene bisphosphonates (99mTc-MDP) bone scan. METHODS: We studied 39 patients with suspected PJI or AL. These patients underwent 68Ga-citrate PET/CT, 99mTc-MDP three-phase bone scan and single-photon emission CT (SPECT)/CT. PET/CT was performed at ten minutes and 60 minutes after injection, respectively. Images were evaluated by three nuclear medicine doctors based on: 1) visual analysis of the three methods based on tracer uptake model, and PET images attenuation-corrected with CT and those not attenuation-corrected with CT were analyzed, respectively; and 2) semi-quantitative analysis of PET/CT: maximum standardized uptake value (SUVmax) of lesions, SUVmax of the lesion/SUVmean of the normal bone, and SUVmax of the lesion/SUVmean of the normal muscle. The final diagnosis was based on the clinical and intraoperative findings, and histopathological and microbiological examinations. RESULTS: Overall, 23 and 16 patients were diagnosed with PJI and AL, respectively. The sensitivity and specificity of three-phase bone scan and SPECT/CT were 100% and 62.5%, 82.6%, and 100%, respectively. Attenuation correction (AC) at 60 minutes and non-AC at 60 minutes of PET/CT had the same highest sensitivity and specificity (91.3% and 100%), and AC at 60 minutes combined with SPECT/CT could improve the diagnostic efficiency (sensitivity = 95.7%). Diagnostic efficacy of the SUVmax was low (area under the curve (AUC) of ten minutes and 60 minutes was 0.814 and 0.806, respectively), and SUVmax of the lesion/SUVmean of the normal bone at 60 minutes was the best semi-quantitative parameter (AUC = 0.969). CONCLUSION: 68Ga-citrate showed the potential to differentiate PJI from AL, and visual analysis based on uptake pattern of tracer was reliable. The visual analysis method of AC at 60 minutes, combined with 99mTc-MDP SPECT/CT, could improve the sensitivity from 91.3% to 95.7%. In addition, a major limitation of our study was that it had a limited sample size, and more detailed studies with a larger sample size are warranted. Cite this article: Bone Joint Res 2022;11(6):398-408.

Head-To-Head Comparison of 68Ga-PSMA-11 PET/CT and 99mTc-MDP Bone Scintigraphy for the Detection of Bone Metastases in Patients With Prostate Cancer: A Meta-Analysis.

BACKGROUND. Bone scintigraphy (BS) using 99mTc-labeled methylene diphospho-nate (99mTc-MDP) remains the recommended imaging modality for the detection of bone metastases in patients with prostate cancer (PCa). However, PET/CT using prostate-specific membrane antigen (PSMA) ligands is increasingly recognized as a means of evaluating disease extent in patients with PCa, including use as a possible stand-alone test in high-risk patients. OBJECTIVE. The purpose of this study is to compare the diagnostic performance of 68Ga-PSMA-11 PET/CT with that of 99mTc-MDP BS for the detection of bone metastases in patients with PCa. EVIDENCE ACQUISITION. The PubMed, Embase, and Cochrane Library databases were searched through October 2021 to identify studies reporting a head-to-head comparison of 68Ga-PSMA-11 PET/CT and 99mTc-MDP BS for the detection of bone metastases in patients with PCa. Only studies with a well-defined reference standard (including various combinations of imaging and/or clinical follow-up) were included. Pooled diagnostic performance was calculated using a bivariate random-effects model, and an AUC was derived for each test from hierarchic summary ROC analysis. The complementary roles of the two tests in identifying bone metastases in patients in whom one of the tests was negative were summarized. EVIDENCE SYNTHESIS. Six studies with 546 patients were included. Pooled sensitivity and specificity, respectively, were 98% (95% CI, 94-99%) and 97% (95% CI, 91-99%) for 68Ga-PSMA-11 PET/CT versus 83% (95% CI, 69-91%) and 68% (95% CI, 41-87%) for 99mTc-MDP BS. The AUC was 0.99 (95% CI, 0.96-1.00) for 68Ga-PSMA-11 PET/CT and 0.85 (95% CI, 0.81-0.87) for 99mTc-MDP BS. Among 408 patients from five included studies, 68Ga-PSMA-11 PET/CT correctly identified bone metastases in 43 of 193 patients (22.3%) with negative 99mTc-MDP BS results, whereas 99mTc-MDP BS correctly identified bone metastases in four of 210 patients (1.9%) with negative 68Ga-PSMA-11 PET/CT results. CONCLUSION. On a per-patient basis, the diagnostic performance of 68Ga-PSMA-11 PET/CT is superior to that of 99mTc-MDP BS for the detection of PCa bone metastases. Furthermore, 99mTc-MDP BS offers limited additional information in patients with negative 68Ga-PSMA-11 PET/CT results. CLINICAL IMPACT. According to current evidence, 99mTc-MDP BS is highly unlikely to be additive to 68Ga-PSMA-11 PET/CT in identifying bone metastases in patients with PCa.

A New Strategy for Rapid Diagnosis of the Source of Low Back Pain in Patients Scheduled to Undergo Treatment with Cooled Radiofrequency Ablation.

OBJECTIVE: The objective of this study was to develop a new strategy for rapid diagnosis of the source of low back pain (LBP) for treatment with cooled radiofrequency ablation (RFA). MATERIALS: Patients suffering from facet joint (FJ) or sacroiliac joint (SIJ) pain for more than 3 months were included. Two methods, Technetium Tc99m methylene diphosphonate single photon emission tomography/computed tomography (99mTc-MDP SPECT/CT) and a modified Fortin finger test were used to identify the source of LBP for treatment with cooled RFA. The visual analog scale (VAS) and Oswestry disability index (ODI) were used to assess the patients' pain levels and disabilities respectively. These two measures were recorded at baseline and 1-week, 1-month, 3-month, and 6-month follow-up visits. RESULTS: A total of 40 patients with LBP were included in this study. Our results demonstrated that the patients with LBP identified by our new strategy had significant improvements in VAS or ODI score at 1-week to 6-month follow-up visits (p < 0.001) after receiving cooled RFA. Similar results were also found in patients with FJ pain and those with FJ and SIJ pain respectively. Among all the patients, over 70% had greater than or equal to 50% reduction in VAS and ODI scores. No serious adverse events were observed after treatment. CONCLUSIONS: This new strategy could be successfully adopted for rapid diagnosis of the source of comprehensive LBP.

Detection of Excess Presence of 99m Tc-MDP Near Injection Site-A Case Report.

Nuclear medicine extravasations and prolonged venous stasis may cause poor quality and quantification errors that can affect image interpretation and patient management. Radiopharmaceutical remaining near the administration site means that some portion of the radioactivity is not circulating as required for the prescribed uptake period. This case describes how detection of excess presence of 99mTc-MDP near the injection site enabled the technologist to apply mitigation tactics early in the uptake process. It also suggests that detecting an extravasation or stasis early in the injection process can be important for image interpretation and minimizing radiation dose to tissue.

Symptomatic Os Navicular on 99mTc-MDP SPECT/CT.

Os navicular bone is an accessory bone of the foot, which is mainly found on the medial side of the proximal navicular bone. Os navicular bone may be symptomatic and cause medial foot pain. We report a case of a 42-year-old athlete male having right foot pain diagnosed with os navicular syndrome on 99mTc-MDP bone scintigraphy SPECT/CT. We emphasize on the use of SPECT/CT in not only allocating the ossicle anatomically, but also for the purpose of evaluating an active source of pain in a region of multiple complex small bones.

Added diagnostic value of SPECT to evaluate bone metastases in breast cancer patients with normal whole body bone scan.

BACKGROUND: In this research, we aimed to survey the added value of single photon emission computed tomography (SPECT) in comparison with planar whole body bone scan to visualize bone metastatic lesions in patients with breast cancer. METHODS: A total of 80 patients with breast cancer (invasive ductal carcinoma) were examined with planar whole body bone scan and SPECT imaging using 99mTc-labelled methylene diphosphonate (99mTc-MDP). The patients with abnormal uptakes in SPECT imaging were also investigated with magnetic resonance imaging (MRI). RESULTS: Among these 80 patients with normal whole body bone SPECT scan, 19 (23.25%) of them revealed abnormal 99mTc-MDP uptake in skeleton. Furthermore, these 19 patients were subjected to MRI and 3 (3.75%) of them were confirmed with metastatic bone lesion. CONCLUSION: The obtained data suggest that SPECT possess the added diagnostic over planar whole body bone scan.

Cutaneous Metastases as Initial Presentation of Lung Carcinoma.

Breast cancer, in women, and lung cancer, in men, are the most common origins of cutaneous metastasis. Lung cancer can metastasize to any organ but mostly to the contralateral lung, liver, adrenal gland, bones, and brain. Over 1-12% of patients with lung cancer can develop skin metastasis. Non-small cell lung cancer includes 87% of lung cancer cases. Adenocarcinomas subtype accounts for approximately 40% of all lung cancers and is the most common histology in women. A woman's lifetime risk of developing lung cancer is 1 in 16 women but lower than that of a man (1 in 13 men). The survival rates of women with lung cancer are usually higher than those of men. Herein, we report the case of a 66-year-old female who presented with painless multiple skin nodules over the chest back and axilla for three months. On evaluation, biopsy and immunohistochemistry were done from skin nodules suggestive of adenocarcinoma. CT thorax showed lung mass and was diagnosed as a case of metastatic adenocarcinoma, primary being from the lung. Our case demonstrated that skin metastasis could be the first sign of internal malignancy. Metastasis to the skin is often a preterminal event that heralds a poor prognosis.

Can the Diagnostic Accuracy of Bone Scintigraphy Be Maintained with Half the Scanning Time?

We aimed to show that the acquisition time of a conventional bone scan could be reduced by half without losing the diagnostic value of the scan. Methods: Fifty adult patients (37 male and 13 female; mean age, 62.5 y; SD, 8.7 y) were enrolled. The patients were injected with 925-1,110 MBq (25-30 mCi) of 99mTc-methylene diphosphonate intravenously. The standard-protocol whole-body planar images were acquired first (scan speed, 10 cm/min; acquisition time, ∼20 min) and were followed immediately by the half-time protocol whole-body planar images (scan speed, 20 cm/min; acquisition time, ∼10 min). Both sets of images were interpreted by 2 nuclear medicine physicians. Each reviewer, when reviewing the standard-protocol images, was self-masked to the result he or she had obtained when reviewing the half-time images, and vice versa. This self-masking was accomplished by allowing a minimum of 2 wk to elapse between the 2 interpretations. We used the κ-coefficient to compare agreement between the standard-protocol results and the half-time results. Results: There was no difference in clinically significant diagnostic information between the half-time and standard protocols. The diagnostic quality of half-time and standard-protocol images did not significantly differ (0.86 < κ < 1.0). Conclusion: Our data suggest that if we reduce the 99mTc-methylene diphosphonate dose by half and keep the acquisition time at its standard value, we gain the benefit of reduced dose without loss of diagnostic value.