[18F] Sodium Fluoride PET Kinetic Parameters in Bone Imaging.

This report describes the significance of the kinetic parameters (k-values) obtained from the analysis of dynamic positron emission tomography (PET) scans using the Hawkins model describing the pharmacokinetics of sodium fluoride ([18F]NaF) to understand bone physiology. Dynamic [18F]NaF PET scans may be useful as an imaging biomarker in early phase clinical trials of novel drugs in development by permitting early detection of treatment-response signals that may help avoid late-stage attrition.

Assessment of quantitative [18F]Sodium fluoride PET measures of knee subchondral bone perfusion and mineralization in osteoarthritic and healthy subjects.

OBJECTIVE: Molecular information derived from dynamic [18F]sodium fluoride ([18F]NaF) PET imaging holds promise as a quantitative marker of bone metabolism. The objective of this work was to evaluate physiological mechanisms of [18F]NaF uptake in subchondral bone of individuals with and without knee osteoarthritis (OA). METHODS: Eleven healthy volunteers and twenty OA subjects were included. Both knees of all subjects were scanned simultaneously using a 3T hybrid PET/MRI system. MRI MOAKS assessment was performed to score the presence and size of osteophytes, bone marrow lesions, and cartilage lesions. Subchondral bone kinetic parameters of bone perfusion (K1), tracer extraction fraction, and total tracer uptake into bone (Ki) were evaluated using the Hawkins 3-compartment model. Measures were compared between structurally normal-appearing bone regions and those with structural findings. RESULTS: Mean and maximum SUV and kinetic parameters Ki, K1, and extraction fraction were significantly different between Healthy subjects and subjects with OA. Between-group differences in metabolic parameters were observed both in regions where the OA group had degenerative changes as well as in regions that appeared structurally normal. CONCLUSIONS: Results suggest that bone metabolism is altered in OA subjects, including bone regions with and without structural findings, compared to healthy subjects. Kinetic parameters of [18F]NaF uptake in subchondral bone show potential to quantitatively evaluate the role of bone physiology in OA initiation and progression. Objective measures of bone metabolism from [18F]NaF PET imaging can complement assessments of structural abnormalities observed on MRI.

18F-Sodium fluoride uptake is associated with severity of atherosclerotic stenosis in stable ischemic heart disease.

BACKGROUND: Increased uptake of 18F-Sodium fluoride (18F-NaF) PET has potential to identify atherosclerotic plaques that are vulnerable to rupture. Whether 18F-NaF PET can evaluate the significance of atherosclerotic plaque in patients with stable coronary artery disease is less clear. We evaluated 18F-NaF PET uptake in coronary arteries in patients without acute coronary artery syndrome to determine the association of 18F-NaF signal uptake with severity of coronary stenosis. METHODS AND RESULTS: We retrospectively identified 114 patients who received both regadenoson stress 82Rb myocardial perfusion PET and 18F-NaF PET study with an average interval of 5 months. Out of this cohort, forty-one patients underwent invasive coronary angiography. In a patient-based analysis, patients with ischemic regadenoson stress 82Rb PET had significantly higher coronary 18F-NaF uptake than patients with normal myocardial perfusion (P < .01). Among the 41 patients who underwent coronary angiography, per-vessel 18F-NaF uptake in both obstructive and nonobstructive coronary arteries was significantly higher than in normal coronary arteries (P < .05) regardless of the severity of coronary calcification. There was poor correlation between calcification and 18F-NaF uptake in coronary arteries (r = 0.41) CONCLUSION: Coronary arterial 18F-NaF uptake is associated with coronary stenosis severity in patients with stable coronary artery disease. 18F-NaF PET studies may be useful for characterizing coronary atherosclerotic plaques.

Temporal relationship between 18F-sodium fluoride uptake in the abdominal aorta and evolution of CT-verified vascular calcification.

BACKGROUND: Fluoride-18 sodium fluoride (18F-NaF) localizes in microcalcifications in atheroma. The microcalcifications may aggregate, passing the resolution threshold to visualize on computed tomography (CT). We evaluated serial NaF positron emission tomography (PET)-CT scans to determine the temporal relationship between vascular NaF uptake and CT evident calcification in the abdominal aorta. METHODS: Prostate cancer patients who had at least 3 NaF PET-CT scans over at least 1.5 years were retrospectively enrolled. Regions of interest were traced in the abdominal aorta on both PET and CT images, excluding skeletal NaF activity. The maximum standardized uptake value (SUVmax) of NaF and the density and volume of calcium (exceeding 130 HU) were summed and divided by the number of slices to produce the SUVmax/slice and the mm3·slice-1 of calcium. RESULTS: Of 437 patients, 45 patients met criteria. NaF uptake waxed and waned between scans, while the calcium volume plateaued or increased over time. NaF uptake correlated with calcium volume on the baseline scan (P = .60, < .0001†) and calcium volume increment, especially from 1.0 to 1.5 years (r = .79, P < .0001†). Patients with persistently high NaF uptake showed a higher calcium volume increment (0-1.5 years) than patients with low or transiently high NaF uptake. CONCLUSIONS: Abdominal aortic NaF uptake varied over time. NaF uptake on the baseline scans and high NaF uptake on the serial scans preceded an increase in calcium volume, especially by 1.0-1.5 years. Persistently high NaF uptake was associated with a greater increment in calcium volume than patients with transiently elevated or persistently low fluoride uptake.

Iterative reconstruction incorporating background correction improves quantification of [18F]-NaF PET/CT images of patients with abdominal aortic aneurysm.

BACKGROUND: A confounding issue in [18F]-NaF PET/CT imaging of abdominal aortic aneurysms (AAA) is the spill in contamination from the bone into the aneurysm. This study investigates and corrects for this spill in contamination using the background correction (BC) technique without the need to manually exclude the part of the AAA region close to the bone. METHODS: Seventy-two (72) datasets of patients with AAA were reconstructed with the standard ordered subset expectation maximization (OSEM) algorithm incorporating point spread function (PSF) modelling. The spill in effect in the aneurysm was investigated using two target regions of interest (ROIs): one covering the entire aneurysm (AAA), and the other covering the aneurysm but excluding the part close to the bone (AAAexc). ROI analysis was performed by comparing the maximum SUV in the target ROI (SUVmax(T)), the corrected cSUVmax (SUVmax(T) - SUVmean(B)) and the target-to-blood ratio (TBR = SUVmax(T)/SUVmean(B)) with respect to the mean SUV in the right atrium region. RESULTS: There is a statistically significant higher [18F]-NaF uptake in the aneurysm than normal aorta and this is not correlated with the aneurysm size. There is also a significant difference in aneurysm uptake for OSEM and OSEM + PSF (but not OSEM + PSF + BC) when quantifying with AAA and AAAexc due to the spill in from the bone. This spill in effect depends on proximity of the aneurysms to the bone as close aneurysms suffer more from spill in than farther ones. CONCLUSION: The background correction (OSEM + PSF + BC) technique provided more robust AAA quantitative assessments regardless of the AAA ROI delineation method, and thus it can be considered as an effective spill in correction method for [18F]-NaF AAA studies.

Clinical implications of 18F-sodium fluoride uptake in subclinical aortic valve calcification: Its relation to coronary atherosclerosis and its predictive value.

BACKGROUND: Uptake of 18F-sodium fluoride (18F-NaF) on positron emission tomography (PET) reflects active calcification. Application of this technique in the early phase of aortic valve calcification (AVC) is of clinical interest. We investigated clinical implications of 18F-NaF uptake in subclinical AVC evaluated simultaneously with coronary atherosclerosis, and the utility of 18F-NaF uptake in predicting AVC progression. METHODS: We studied 25 patients with subclinical AVC and coronary plaques detected on computed tomography (CT) who underwent 18F-NaF PET/CT. AVC score, volume, mean density, and the presence of high-risk coronary plaque were evaluated on CT in each patient. Focal 18F-NaF uptake in AVC and in coronary plaques was quantified with the maximum tissue-to-background ratio (TBRmax). RESULTS: There were positive correlations between AVC TBRmax (A-TBRmax) and AVC parameters on CT. The 14 patients with high-risk coronary plaque had significantly higher A-TBRmax than those without such plaque (1.60 ± 0.18 vs 1.42 ± 0.13, respectively; P = 0.012). A-TBRmax positively correlated with maximum TBRmax of coronary plaque per patient (r = 0.55, P = 0.0043). In the 11 patients who underwent follow-up CT scan, A-TBRmax positively correlated with subsequent increase in AVC score (r = 0.74, P = 0.0091). CONCLUSION: Our 18F-NaF PET- and CT-based data indicate relationships between calcification activity in subclinical AVC and characteristics of coronary atherosclerosis. 18F-NaF PET may provide new information regarding molecular conditions and future progression of subclinical AVC.

Detecting native and bioprosthetic aortic valve disease using 18F-sodium fluoride: Clinical implications.

Calcific aortic valve disease is the most common valvular disease and confers significant morbidity and mortality. There are currently no medical therapies that successfully halt or reverse the disease progression, making surgical replacement the only treatment currently available. The majority of patients will receive a bioprosthetic valve, which themselves are prone to degeneration and may also need replaced, adding to the already substantial healthcare burden of aortic stenosis. Echocardiography and computed tomography can identify late-stage manifestations of the disease process affecting native and bioprosthetic aortic valves but cannot detect or quantify early molecular changes. 18F-fluoride positron emission tomography, on the other hand, can non-invasively and sensitively assess disease activity in the valves. The current review outlines the pivotal role this novel molecular imaging technique has played in improving our understanding of native and bioprosthetic aortic valve disease, as well as providing insights into its feasibility as an important future research and clinical tool.

Spectrum of false positive 18F-sodium fluoride (NaF) bone PET/CT findings in Oncology imaging; A narrative pictorial review of cases from a single institution.

Fluorine-18-sodium fluoride (18F-NaF) is a positron emission tomography (PET) bone imaging agent mainly used for oncology staging but may also be used in the evaluation of benign bone and joint pathology conditions. Fluorine-18-NaF is an excellent bone-seeking agent with high bone uptake owing to favorable biodistribution with rapid single-pass extraction, limited plasma protein binding and prompt renal clearance. Fluorine-18-NaF PET/computed tomography (CT) is highly sensitive in identifying both sclerotic and lytic bone metastatic lesions. Occasionally 18F-NaF uptake in benign bone lesions can mimic malignantpathology. In these cases, the pattern of 18F-NaF uptake may elicit a specific diagnosis and correlation with clinical information and morphological information from correlative CT is essential for a correct diagnosis. In the present article, we present a series of clinical cases demonstrating examples of 18F-NaF uptake in benign lesions which can simulate malignant pathology in patients undergoing cancer staging.

Prediction of Response to Tumor Necrosis Value-α Blocker Is Suggested by 18F-NaF SUVmax But Not by Quantitative Pharmacokinetic Analysis in Patients With Ankylosing Spondylitis.

OBJECTIVE. We aimed to evaluate the pharmacokinetics and maximum standardized uptake value (SUVmax) of 18F-NaF PET/CT for assessment of disease activity and prediction of response in patients with ankylosing spondylitis (AS). MATERIALS AND METHODS. Twenty-seven patients (age, interquartile range, 30.25-49.75 years) with AS who were receiving a tumor necrosis factor-α (TNF-α) blocker were included. All patients underwent dynamic PET of the pelvis followed by whole-body PET/CT. Quantitative analysis of kinetic data of the sacroiliac joints (SIJs) was performed, and the SUVmax of the SIJs and SUVmax of the spine were calculated. Clinical indexes related to AS disease activity (serum C-reactive protein level, Bath ankylosing spondylitis disease activity index [ BASDAI], and Bath ankylosing spondylitis functional index) were evaluated. Clinical response was defined as an improvement from the initial BASDAI score of 50% or more (BASDAI 50) within 2 years after baseline 18F-NaF PET/CT. RESULTS. The BASDAI score at 18F-NaF PET/CT was significantly different between the responders and nonresponders: 18F-NaF uptake at the spine was significantly higher in the responders than in the nonresponders. Only SUVmax of the spine had a significant positive correlation with BASDAI score at PET/CT (r = 0.38, p = 0.048). The BASDAI score at PET/CT (odds ratio [OR], 35.32; 95% CI, 2.09-57.84; p = 0.014) and SUVmax of the spine (OR, 14.69; 95% CI, 0.79-27.27; p = 0.027) were significantly associated with BASDAI 50 response prediction. CONCLUSION. The results of our study suggest that the SUVmax of the spine on whole-body 18F-NaF PET/CT is a reliable and noninvasive biomarker for predicting therapeutic response to TNF-α blocker and shows better performance for predicting response than quantitative pharmacokinetic parameters. Fluorine-18-labeled NaF PET/CT showed axial bone lesions with bone formation and can be used as a monitoring tool in patients with AS receiving anti-TNF-α drugs. However, these results need to be validated in a larger cohort.

Relationship between lower lumbar spine shape and patient bone metabolic activity as characterised by 18F NaF bio-markers.

Chronic lower lumbar pain has been associated with elevated bone metabolic activity in the spine. Diagnosis of bone metabolic activity is currently through integrating Positron Emission Tomography (PET) with Sodium Fluoride (18F-NaF) biomarkers. It has been reported that numerous observable pathologies including lumbar fusion, disc abnormalities and scoliosis have often been associated with increased 18F-NaF uptake. The aim of this study was to identify what features of lower lumbar shape most strongly correlate with 18F-NaF uptake. Following a principal component analysis of 23 patients who presented with lumbar pain and underwent 18F-NaF PET-CT, it was revealed that three modes interpreted as (i) sacral tilt, (ii) vertebral disc spacing and (iii) spine size were the three characteristics that described 88.7% of spine shape in our study population. 18F-NaF was described by two modes including 18F-NaF intensity and spatial variation (anterior-inferior to posterior-superior). 18F-NaF was most sensitive to sacral tilt followed by vertebral disc spacing. A predictive model derived from that spine population was able to predict 18F-NaF 'hot-spot' locations with 85 ±â€¯5% accuracy and with 71 ±â€¯3% accuracy for the 18F-NaF magnitude. These results suggest that patients reporting with lower lumbar pain and who present with increased sacral tilt profiles and/or reduced disc spacing are good candidates for further 18F-NaF PET-CT imaging, evidenced by the high association between those shape profiles and 18F-NaF uptake.

Vulnerable plaque imaging using 18F-sodium fluoride positron emission tomography.

Positron emission tomography (PET) with 18F-sodium fluoride (18F-NaF) has emerged as a promising non-invasive imaging modality to identify high-risk and ruptured atherosclerotic plaques. By visualizing microcalcification, 18F-NaF PET holds clinical promise in refining how we evaluate coronary artery disease, shifting our focus from assessing disease burden to atherosclerosis activity. In this review, we provide an overview of studies that have utilized 18F-NaF PET for imaging atherosclerosis. We discuss the associations between traditional coronary artery disease measures (risk factors) and 18F-NaF plaque activity. We also present the data on the histological validation as well as show how 18F-NaF uptake is associated with plaque morphology on intravascular and CT imaging. Finally, we discuss the technical challenges associated with 18F-NaF coronary PET highlighting recent advances in this area.

The clinical significance of incidental soft tissue uptake on whole body 18F-sodium fluoride bone PET-CT.

18F-sodium fluoride (NaF) is a PET bone imaging agent and is commonly used in imaging patients with cancer; however, similar to technetium-99m medronic acid (99mTc-MDP), it can be useful in the evaluation of benign bone and joint conditions. NaF is an excellent bone-seeking agent with high bone uptake due to rapid single-pass extraction. It has negligible plasma protein binding, rapid blood, renal clearance, high bone uptake and almost all NaF delivered is retained by bone after a single pass of blood; however, uptake of NaF can be observed in non-osseous structures such as the arterial vasculature, gastrointestinal tract, genitourinary tract, and viscera. In this article, we present a spectrum of clinical cases with non-osseous NaF uptake in patients referred for cancer staging.

Feasibility of Coronary 18F-Sodium Fluoride Positron-Emission Tomography Assessment With the Utilization of Previously Acquired Computed Tomography Angiography.

BACKGROUND: We assessed the feasibility of utilizing previously acquired computed tomography angiography (CTA) with subsequent positron-emission tomography (PET)-only scan for the quantitative evaluation of 18F-NaF PET coronary uptake. METHODS AND RESULTS: Forty-five patients (age 67.1±6.9 years; 76% males) underwent CTA (CTA1) and combined 18F-NaF PET/CTA (CTA2) imaging within 14 [10, 21] days. We fused CTA1 from visit 1 with 18F-NaF PET (PET) from visit 2 and compared visual pattern of activity, maximal standard uptake (SUVmax) values, and target to background ratio (TBR) measurements on (PET/CTA1) fused versus hybrid (PET/CTA2). On PET/CTA2, 226 coronary plaques were identified. Fifty-eight coronary segments from 28 (62%) patients had high 18F-NaF uptake (TBR >1.25), whereas 168 segments had lesions with 18F-NaF TBR ≤1.25. Uptake in all lesions was categorized identically on coregistered PET/CTA1. There was no significant difference in 18F-NaF uptake values between PET/CTA1 and PET/CTA2 (SUVmax, 1.16±0.40 versus 1.15±0.39; P=0.53; TBR, 1.10±0.45 versus 1.09±0.46; P=0.55). The intraclass correlation coefficient for SUVmax and TBR was 0.987 (95% CI, 0.983-0.991) and 0.986 (95% CI, 0.981-0.992). There was no fixed or proportional bias between PET/CTA1 and PET/CTA2 for SUVmax and TBR. Cardiac motion correction of PET scans improved reproducibility with tighter 95% limits of agreement (±0.14 for SUVmax and ±0.15 for TBR versus ±0.20 and ±0.20 on diastolic imaging; P<0.001). CONCLUSIONS: Coronary CTA/PET protocol with CTA first followed by PET-only allows for reliable and reproducible quantification of 18F-NaF coronary uptake. This approach may facilitate selection of high-risk patients for PET-only imaging based on results from prior CTA, providing a practical workflow for clinical application.

Subgingival uptake and retention of stannous fluoride from dentifrice: Gingival crevicular fluid concentrations in sulci post-brushing.

PURPOSE: To examine the delivery of stannous fluoride to subgingival sulci following toothpaste use in a clinical population. METHODS: This was a controlled, single-site study. 23 subjects with at least 20 dental pockets, 2-4 mm with bleeding, who had not used a stannous fluoride dentifrice in the last 3 months were enrolled. After a 2-week washout period, 20 subjects returned for a baseline visit. They were instructed to refrain from brushing the night before the baseline visit. GCF samples were taken from up to 10 sites identified as sampling sites. Subjects were then given a 0.454% stannous fluoride dentifrice and soft manual toothbrush and asked to brush for 1 minute. 30 minutes after brushing, GCF was re-sampled. Subjects continued using the stannous fluoride dentifrice and soft manual toothbrush at home, twice daily for 2 weeks, in place of their usual hygiene products. At Days 1 and 14, subjects returned to the site, and 12 hours post-brushing GCF samples were taken. The samples were analyzed by ICP-MS (inductively coupled plasma mass spectrometry). A Wilcoxon signed-rank test was performed to determine the difference between post-baseline visits and baseline. Statistical tests were 2-sided using a 5% significance level. RESULTS: 20 subjects completed the trial. Significant levels of tin, a marker for stannous fluoride, were detected 30 minutes after brushing at sampling sites of 2-4 mm. The median tin level in gingival crevicular fluid (GCF) was 24.59 ng/µl, which was highly significant versus baseline (P< 0.0001). Tin levels sampled in GCF 12 hours after brushing on Days 1 and 14 were highly significant versus Baseline (P< 0.0001), showing an increasing trend with continued use. CLINICAL SIGNIFICANCE: Stannous fluoride was found to penetrate sampling sites from 2-4 mm and was retained for 12 hours. Subgingival uptake and retention of stannous fluoride following toothbrushing may play a role in detoxification effects on microbial biofilms and may contribute to the therapeutic efficacy of stannous fluoride dentifrices in promoting gingival health.

18F-Sodium Fluoride Uptake in Abdominal Aortic Aneurysms: The SoFIA3 Study.

BACKGROUND: Fluorine-18-sodium fluoride (18F-NaF) uptake is a marker of active vascular calcification associated with high-risk atherosclerotic plaque. OBJECTIVES: In patients with abdominal aortic aneurysm (AAA), the authors assessed whether 18F-NaF positron emission tomography (PET) and computed tomography (CT) predicts AAA growth and clinical outcomes. METHODS: In prospective case-control (n = 20 per group) and longitudinal cohort (n = 72) studies, patients with AAA (aortic diameter >40 mm) and control subjects (aortic diameter <30 mm) underwent abdominal ultrasound, 18F-NaF PET-CT, CT angiography, and calcium scoring. Clinical endpoints were aneurysm expansion and the composite of AAA repair or rupture. RESULTS: Fluorine-18-NaF uptake was increased in AAA compared with nonaneurysmal regions within the same aorta (p = 0.004) and aortas of control subjects (p = 0.023). Histology and micro-PET-CT demonstrated that 18F-NaF uptake localized to areas of aneurysm disease and active calcification. In 72 patients within the longitudinal cohort study (mean age 73 ± 7 years, 85% men, baseline aneurysm diameter 48.8 ± 7.7 mm), there were 19 aneurysm repairs (26.4%) and 3 ruptures (4.2%) after 510 ± 196 days. Aneurysms in the highest tertile of 18F-NaF uptake expanded 2.5× more rapidly than those in the lowest tertile (3.10 [interquartile range (IQR): 2.34 to 5.92 mm/year] vs. 1.24 [IQR: 0.52 to 2.92 mm/year]; p = 0.008) and were nearly 3× as likely to experience AAA repair or rupture (15.3% vs. 5.6%; log-rank p = 0.043). CONCLUSIONS: Fluorine-18-NaF PET-CT is a novel and promising approach to the identification of disease activity in patients with AAA and is an additive predictor of aneurysm growth and future clinical events. (Sodium Fluoride Imaging of Abdominal Aortic Aneurysms [SoFIA3]; NCT02229006; Magnetic Resonance Imaging [MRI] for Abdominal Aortic Aneurysms to Predict Rupture or Surgery: The MA3RS Trial; ISRCTN76413758).

Uptake of Radium-223 Dichloride and Early [18F]NaF PET Response Are Driven by Baseline [18F]NaF Parameters: a Pilot Study in Castration-Resistant Prostate Cancer Patients.

PURPOSE: The purpose of this study is to identify predictive factors on baseline [18F]NaF positron emission tomography (PET)/computed tomography (CT) of early response to radium-223 dichloride after 3 cycles of treatment in metastatic castration-resistant prostate cancer patients. PROCEDURES: Analysis of 152 metastases was performed in six consecutive patients who underwent [18F]NaF PET/CT at baseline and for early monitoring after 3 cycles of radium-223 dichloride. All metastases depicted on whole-body [18F]NaF PET/CT were contoured and CT (density in Hounsfield units, sclerotic, mixed, or lytic appearance) as well as [18F]NaF [maximum standardized uptake value (SUVmax), SUVmean, and lesion volume (V18F-NaF)] patterns were recorded. Tumor response was defined as percentage change in SUVmax and SUVmean between baseline and post-treatment PET. Bone lesions were defined as stable, responsive, or progressive, according to thresholds derived from a recent multicentre test-retest study in [18F]NaF PET/CT. Total [18F]NaF uptake in metastases, defined as MATV × SUVmean, was correlated to uptake of radium-223 on biodistribution scintigraphy performed 7 days after the first cycle of treatment. RESULTS: Among metastases, 116 involved the axial skeleton and 36 the appendicular skeleton. Lesions were sclerotic in 126 cases and mixed in 26 cases. No lytic lesion was depicted. ROC analysis showed that SUVmax and SUVmean were better predictors of lesion response than V18F-NaF and density on CT (P < 0.0001 and P = 0.001, respectively). SUVmax and SUVmean were predictors of individual tumor response in separate multivariate models (P = 0.01 and P = 0.02, respectively). CT pattern (mixed versus sclerotic) and lesion density were independent predictors only when assessing response with delta SUVmax (P = 0.002 and 0.007, respectively). A good correlation between total [18F]NaF uptake within metastases and their relative radium-223 uptake assessed by two observers 7 days after treatment (r = 0.72 and 0.77, P < 0.0001) was found. CONCLUSIONS: SUVmax and SUVmean on baseline [18F]NaF PET/CT are independent predictors of bone lesions' response to 3 cycles of radium-223 dichloride, supporting the use of NaF to select patients more likely to respond to treatment.

Na18F accumulates on the compressive side of peri-implant bone under immediate loading.

This study aimed to examine the dynamic change in bone metabolism by immediate loading in several sites around implants using high-resolution Na18F-PET scan. Two titanium implants (Ø 1.2 mm) were inserted parallel to each other in the right tibiae of Wistar rats (n = 4). The left tibia was set as control side. One day after insertion, closed coil springs of 4.0 N were attached to the expose superior portions of the implants to apply a continuous mechanical stress. The rats with fluorine-18 (18F) ion (5 mCi/rat) intravenously injected were scanned by PET scanner at 4, 7, 14, 28 days after load application. Round region of interests (ROIs) were set around the distal implant of the right tibia (loaded side) and same site (control) of the left tibia. Furthermore, four rectangular ROIs were set at the superior and inferior parts of traction side (mesial) and opposite side (distal) of the distal implant. Longitudinal dynamic changes in bone metabolism were evaluated by examination of the accumulation count of 18F ion at each ROI. The uptake values of ROIs (loaded side) initially increased until 7 days, and they gradually decreased from the peak level to the pre-loading level despite a static force being applied to the implants. In cancellous bone, the uptake values at the superior part of traction side and inferior part of opposite side showed significantly high value compared with those at other parts. In conclusion, immediate loading to the implant initially enhanced bone metabolism around it, especially at the part with compressive stress. Peri-implant bone metabolism varies according to different loading conditions.