A new method for assessing 99Tcm-MDP bone uptake from a bone scan image: quantitative measurement of radioactivity in global skeletal regions of interest

Frequent, quantitative bone planar scintigraphy for determination of bone anabolism in growing mice

Background

To provide insight into bone turnover, quantitative measurements of bone remodeling are required. Radionuclide studies are widely used in clinical care, but have been rarely used in the exploration of the bone in preclinical studies. We describe a bone planar scintigraphy method for frequent assessment of bone activity in mice across the growing period. Since repeated venous radiotracer injections are hardly feasible in mice, we investigated the subcutaneous route.

Methods

Repeated ^99mTc-hydroxymethylene diphosphonate (HMDP) tracer bone planar scintigraphy studies of the knee region and µCT to measure femur growth rate were performed in eight mice between week 6 and week 27 of life, i.e., during their growth period. Three independent investigators assessed the regions of interest (ROI). An index was calculated based on the counts in knees ROI (normalized by pixels and seconds), corrected for the activity administered, the decay between administration and imaging, and individual weights.

Results

A total of 93 scintigraphy studies and 85 µCT were performed. Repeated subcutaneous tracer injections were well tolerated and allowed for adequate radionuclide studies. Mean scintigraphic indexes in the knees ROI decreased from 87.4 ± 2.6 × 10⁻⁶ counts s⁻¹ pixel⁻¹ MBq⁻¹ g⁻¹ at week 6 to 15.0 ± 3.3 × 10⁻⁶ counts s⁻¹ pixel⁻¹ MBq⁻¹ g⁻¹ at week 27. The time constant of the fitted exponential decay was equal to 23.5 days. As control mean femur length assessed by µCT increased from 12.2 ± 0.8 mm at week 6 to 15.8 ± 0.2 mm at week 22. The time constant of the fitted Gompertz law was equal to 26.7 days. A correlation index of −0.97 was found between femur growth and decrease of bone tracer activity count between week 6 and 24.

Conclusion

This methodological study demonstrates the potential of repeated bone planar scintigraphy in growing mice, with subcutaneous route for tracer administration, for quantitative assessment of bone remodeling.

Quantitative studies of bone using (99m)Tc-methylene diphosphonate skeletal plasma clearance

Quantitative bone scan imaging has a useful role in research for examining the pathophysiology of metabolic bone diseases and the response of patients to treatment. The advantage of nuclear medicine imaging as a way of measuring the rate of bone remodeling is that either the whole skeleton or discrete regions of interest (ROIs) may be studied depending on whether there is diffuse or localized disease. This article reviews methods of quantifying (99m)Tc-methylene diphosphonate ((99m)Tc-MDP) kinetics based on a standard bone scan examination by measuring the plasma clearance of tracer to the whole skeleton and/or selected ROIs drawn on the bone scan image. Although the measurement of bone plasma clearance requires blood sampling to find the input curve for free (eg, nonprotein bound) (99m)Tc-MDP, we argue that plasma clearance studies give a more physiological approach in a better accord with the underlying changes in bone turnover than conventional measurements of whole-body retention or bone uptake. We describe 3 methods of measuring whole-skeleton (99m)Tc-MDP plasma clearance (K(bone)): (1) the area under the curve (AUC) method based on taking 6 blood samples at 5, 15, 60, 120, 180, and 240 minutes and measuring the plasma concentration of free (99m)Tc-MDP by ultrafiltration using a 30-kDa filter. The AUC method requires a simultaneous measurement of glomerular filtration rate using (51)Cr-EDTA as a cotracer; (2) the modified Brenner method, which measures K(bone) by drawing a soft-tissue ROI over the adductor muscles and plotting the soft tissue counts at 1, 2, 3, and 4 hours against the AUC values at the corresponding time points; (3) the Patlak method based on combining gamma camera measurements of whole-body retention with plasma data and measuring K(bone) from the slope of the Patlak plot fitted to the 2, 3, and 4 hours data points. Unlike the first 2 methods, the Patlak plot can also be used to measure regional values of K(bone) for any chosen ROI. Initial studies have shown good agreement between the 3 methods of measuring K(bone), and highly significant correlations between the change in K(bone) values during treatment and the corresponding changes in serum and urinary measurements of biochemical markers of bone formation and bone resorption.

Bone turnover markers are correlated with total skeletal uptake of 99mTc-methylene diphosphonate (99mTc-MDP)

Background

Skeletal uptake of ^99mTc labelled methylene diphosphonate (^99mTc-MDP) is used for producing images of pathological bone uptake due to its incorporation to the sites of active bone turnover. This study was done to validate bone turnover markers using total skeletal uptake (TSU) of ^99mTc-MDP.

Methods

22 postmenopausal women (52–80 years) volunteered to participate. Scintigraphy was performed by injecting 520 MBq of ^99mTc-MDP and taking whole body images after 3 minutes, and 5 hours. TSU was calculated from these two images by taking into account the urinary loss and soft tissue uptake. Bone turnover markers used were bone specific alkaline phosphatase (S-Bone ALP), three different assays for serum osteocalcin (OC), tartrate resistant acid phosphatase 5b (S-TRACP5b), serum C-terminal cross-linked telopeptides of type I collagen (S-CTX-I) and three assays for urinary osteocalcin (U-OC).

Results

The median TSU of ^99mTc-MDP was 23% of the administered activity. All bone turnover markers were significantly correlated with TSU with r-values from 0.52 (p = 0.013) to 0.90 (p < 0.001). The two resorption markers had numerically higher correlations (S-TRACP5b r = 0.90, S-CTX-I r = 0.80) than the formation markers (S-Total OC r = 0.72, S-Bone ALP r = 0.66), but the difference was not statistically significant. TSU did not correlate with age, weight, body mass index or bone mineral density.

Conclusion

In conclusion, bone turnover markers are strongly correlated with total skeletal uptake of ^99mTc-MDP. There were no significant differences in correlations for bone formation and resorption markers. This should be due to the coupling between formation and resorption.

Short-time ingestion of colas influences the activity distribution at bone scintigraphy: experimental studies in the mouse

BACKGROUND

A negative effect of soft drinks, especially phosphate containing colas, on bone mineral contents has been reported. Most studies have been epidemiological investigations or performed in healthy humans.

OBJECTIVE

The aim was to study the effect of short-time ingestion of Coca-Cola, a phosphate containing soft drink, and of Fanta, a non-phosphate containing soft drink, in a murine system for bone scintigraphy. This technique may be used to study bone metabolism.

DESIGN AND METHODS

After feeding the beverages to the mice during different time periods (2 h to 6 days), the animals were injected with the bone-seeking radiopharmaceutical. The activity distribution was thereafter mapped by dissecting the hind legs and different soft tissue organs and assessing their activity with a gamma-counter. Controls were mice drinking water.

RESULTS

After drinking Coca-Cola there was a significantly increased bone uptake of the tracer and a reduced uptake by most soft tissues versus controls. After Fanta there were no differences. Comparing Coca-Cola and Fanta, there was a significantly lower uptake by all soft tissues after Coca-Cola, but no significant difference for bone.

CONCLUSIONS

Short-time ingestion of Coca-Cola in mice causes an increased bone uptake and a reduced soft tissue uptake at bone scintigraphy. There may be a similar, weaker effect by Fanta. This is in agreement with previous studies indicating that soft drinks may, on their own, have a metabolic effect on the bone.

Does cisplatin chemotherapy decrease the MDP uptake of normal bone? An experimental study

OBJECTIVE

Bone scan is the accepted initial imaging modality for skeletal metastases. Cisplatin is a cell-cycle nonspecific antineoplastic agent used in some chemotherapy regimens. Knowing that platinum reacts with phosphate compounds such as methylenediphosphonic acid (MDP), decreases bone resorption and new bone formation, it can be proposed that cisplatin chemotherapy may decrease Tc-99m MDP bone uptake. We aimed to demonstrate, if present, the decrease in bone uptake and to determine the duration of this effect.

METHODS

Thirty male Wistar rats were randomized into five groups, namely, placebo group (G1) and cisplatin groups (G2, G3, G4, G5). Pre-therapy bone scintigraphies were obtained in all the groups. Cisplatin chemotherapy was given as infusion. Post-therapy bone scintigraphies were obtained 10 min, 1 h, 24 h, and 72 h after chemotherapy in groups G2-G5, respectively. A placebo bone scintigraphy was obtained 10 min after infusion of serum physiologic in G1. Plasma samples for cisplatin plasma values were obtained. The graphite furnace atomic absorption spectrophotometry technique was used for cisplatin analysis. Quantitative analysis (bone uptake ratios) was performed by drawing regions of interest on the right femur, vertebral column, and adjacent soft tissues. The injection/examination time delay and the net injected MDP doses were also noted.

RESULTS

There was no statistically significant difference in bone uptake values, injected MDP doses or injection/examination time delay in any group. Cisplatin plasma values were significantly different in G2, G3, G4, and G5 (P < 0.05) but not in G1.

CONCLUSIONS

Cisplatin chemotherapy seems to have no effect on the Tc-99m MDP uptake of normal bone.

An instrument to measure skeletal burden and predict functional outcome in fibrous dysplasia of bone

An instrument to measure skeletal burden in fibrous dysplasia was developed. Biological and clinical relevance was shown by correlating skeletal burden scores with bone markers, quality of life, and ambulatory status. Childhood scores predict adult ambulatory status, and scores were unaffected when bone markers decreased with bisphosphonate treatment or aging.

INTRODUCTION

Fibrous dysplasia (FD) is a skeletal disease with a broad clinical expression. There is no objective method to assess the extent of skeletal involvement or predict outcome. We developed an instrument to measure skeletal burden that correlates with physical function, health-related quality of life (HRQL), and ambulatory status.

MATERIALS AND METHODS

Seventy-nine patients with FD underwent bone scintigraphy. The skeletal burden score was derived from a weighted score based on the regional measurement using bone scintigraphy to estimate the amount of FD in anatomical segments. Six readers scored 20 scans twice to determine the inter- and intrareader agreement. To assess biological significance, scores were correlated with bone markers. To assess functional outcome, scores on the SF-36 (adults) or CHQ-PF50 (children) were correlated with skeletal burden scores. In a group of patients who had bone scans as children and adults (n = 6), the ability to predict ambulatory status was tested. Skeletal burden scores were assessed in patients before and after treatment with pamidronate (n = 5).

RESULTS

The inter- and intrareader agreement of burden scores were r = 0.96, and 0.98, respectively (p < 0.001 for both). The scores correlated with markers of bone metabolism and HRQL (Spearman rho, 0.54-0.67 p < 0.001 and -0.43, p = 0.001, respectively). The mean score of patients who ambulated unassisted was significantly lower than those requiring assistance (p < 0.001 unassisted versus crutch and/or wheelchair). In unassisted ambulators, younger patients had higher scores, suggesting high childhood scores may predict adulthood impairment. In six patients with childhood and adulthood scans, childhood scores >30 predicted assisted ambulation in adulthood. There was a negative correlation between bone markers and age (Spearman rho, -0.42 to -0.70; p < 0.001), but not age and skeletal burden score. Pamidronate treatment decreased serum alkaline phosphatase but had no effect on the skeletal burden score.

CONCLUSIONS

This is a validated and reliable instrument for the measurement of skeletal burden of FD and is able to predict functional outcome.

A direct in vivo measurement of 99mTc-methylene diphosphonate protein binding

Quantitative studies of the kinetics of 99mTc-methylene diphosphonate (99mTc-MDP) in metabolic and metastatic bone disease require the measurement of free tracer in plasma to derive the input function. We describe a simple method of determination of free 99mTc-MDP in vivo based on measurements of the ratio of the renal plasma clearances of total 99mTc-MDP and 51Cr-ethylenediaminetetraacetic acid (51Cr-EDTA). The method is based on evidence that free MDP is cleared through the kidneys by glomerular filtration. Measurements of the fraction of free 99mTc-MDP were made between 0 and 4 h after injection in 70 postmenopausal women enrolled in a study of the effect of hormone replacement therapy on the whole-skeleton plasma clearance of 99mTc-MDP (K(bone)). The glomerular filtration rate (GFR) was measured simultaneously from the plasma clearance of 51Cr-EDTA. The mean fractions (and SD) of free MDP measured were 0.757 (0.050), 0.663 (0.062), 0.550 (0.052) and 0.472 (0.053), respectively, at 17, 90, 150 and 210 min after injection. The results agreed closely with data using protein precipitation with trichloroacetic acid. Between 2 and 4 h after injection, the biological half-life of free 99mTc-MDP in plasma was 92 min, compared with 540 min for bound MDP. Highly significant relationships were found between the fraction of free MDP measured in each patient at each of the four time points and the total plasma clearance of free 99mTc-MDP (K(total)=GFR+K(bone)), such that a larger value of K(total) was associated with a smaller fraction of free MDP. Multivariate regression analysis confirmed that this relationship held individually for both GFR and K(bone). A strong inverse relationship was found between K(total) and the plasma concentration of free 99mTc-MDP, but a much weaker relationship with the bound MDP concentration, a finding that is consistent with the slow re-equilibration of bound MDP in the circulation. The results confirm that the fraction of free 99mTc-MDP varies with time and shows significant differences between individuals, which are dependent on GFR and K(bone) amongst other factors.

Radioimaging of implants in rats using Tc-99m-MDP

Radiopharmaceutical isotopes are widely used clinically to detect tumors of osteogenic origin. One example is Technetium-99m methylene diphosphonate (Tc-99m-MDP). When viewed with a gamma camera, the concentration of the isotope (increased gamma activity) indicates an area of increased bone activity. This technology provides an opportunity to measure bone growth around implants in vivo. The purpose of this study was to measure Tc-99m-MDP activity around titanium alloy implants placed in the tibiae of rats. Some implant sites were treated with a growth factor; other sites served as controls. The hypothesis tested was that implants placed with a growth factor would have greater associated Tc-99m-MDP activity. Twelve adult male Sprague-Dawley rats were anesthetized and surgical access to the medial proximal tibiae was obtained. Titanium alloy screw implants were placed in six animals along with 65 microgram of acidic fibroblast growth factor (FGF-1); the other six animals received implants only and served as controls. After five days, rats were injected with 1500 microCi of Tc-99m-MDP. After 3 hours, rats were imaged with a gamma camera. The Tc-99m-MDP intensity associated with each implant was quantified and the means for each group were compared using ANOVA. Implants treated with FGF-1 demonstrated significantly more Tc-99m-MDP activity than implants alone. This suggests that Tc-99m-MDP analysis may be a useful tool for determining bone growth around implants in laboratory animals in vivo.

Quantitative studies of bone with the use of 18F-fluoride and 99mTc-methylene diphosphonate

This article discusses methods for quantifying bone turnover based on tracer kinetic studies of the short-lived radiopharmaceuticals 99mTc-MDP and 18F-fluoride. Measurements of skeletal clearance obtained by using these tracers reflect the combined effects of skeletal blood flow and osteoblastic activity. The pharmacokinetics of each tracer is described, together with some of the quantitative tests of skeletal function that have been described in the literature. The physiologic interpretation of quantitative measurements of bone obtained with the use of short half-life radionuclides is discussed, and the advantages and limitations of 99mTc-MDP and 18F-fluoride are compared and contrasted. Currently, 18F-fluoride dynamic positron emission tomography (PET) is the technique of choice for physiologically precise quantitative studies of bone. However, comparable data could probably be obtained by using 99mTc-MDP if methods for single photon emission computed tomography (SPECT) quantitation were improved.

Relationship between skeletal uptake of 99mTc-HMDP and bone mineral density in elderly women

The relationship between bone mineral density in elderly women and the pattern of skeletal uptake of 99mTc-HMDP, especially in regard to skull uptake, was investigated. The whole-body skeletal uptake (WBSU) and whole-body skeletal tracer distribution patterns were studied in 86 disease-free women on bone scintigraphy with 99mTc-hydroxy-methylene-diphosphonate (HMDP). Bone scans were quantified by setting regions of interest (ROI) and bone mineral density (BMD) was assessed by dual-energy X-ray absorptiometry in all patients. WBSU and the skeletal distribution pattern were compared with bone mineral densities of the entire skeleton as well as selected regions. WBSU was high in the elderly and negatively correlated with regional bone mineral densities (r = -0.403 to -0.534). Among the regions, uptake by the skull increased with age more than in other regions in women and had the highest negative correlation with the bone mineral density. The skull uptake correlated negatively with total body BMD (r = -0.583) and with lumbar BMD (r = -0.561, p < 0.0001). Our results show that increased radionuclide uptake in bone scintigraphy, especially skull uptake was associated with decreased bone mineral density in elderly women, so that, increased skull uptake in elderly women would be a scintigraphic sign of post-menopausal or senile osteopenia.

Age-related changes in the global skeletal uptake of technetium-99m methylene diphosphonate in healthy women

A short-term evaluation of global skeletal uptake (GSU) of technetium-99m methylene diphosphonate (MDP) was performed in 40 healthy female subjects with a wide age range in order to investigate the clinical performance of the technique and to detect the age-related changes in bone turnover. The results obtained were compared with measurements of the main biochemical markers of skeletal metabolism. We found that GSU increases progressively with age, independently of concomitant changes in renal function; significant correlations with biochemical markers of bone formation were also found. Therefore, the method appears to provide useful information concerning the bone turnover rate, and is also applicable to elderly people owing to its simplicity.

Effects of continuous percutaneous estradiol administration on skeletal turnover in postmenopausal women: a 1-year prospective controlled study

The aim of this study was to investigate the short and long term effects of continuous percutaneous administration of estradiol (E2) cream on skeletal turnover in women in surgical postmenopause. Forty women were randomly divided into two groups, one treated with a single daily application of 3 mg/day E2 cream continuously for 12 months, the other receiving placebo cream. Forearm densitometry was performed before and at the end of treatment. Serum E2, osteocalcin (BGP), alkaline posphatase (AP) and urinary N-telopeptide of type I collagen (NTX) were also measured at baseline, month 4 and 12 of the protocol. At month 4, bone turnover was also assessed by evaluating 99mtechnetium-methylene diphosphonate (99mTc-MDP) skeletal uptake. Changes in E2, BGP, AP and NTX as well as 99mTc-MDP skeletal uptake in hormone group vs. placebo were significant after 4 months of treatment. At month 12, proximal site densitometry showed no variation in either group whereas the percentage of variation in distal site measurements resulted significantly different with an increase in the hormone group and a reduction in the placebo group. In conclusion continuous percutaneous administration of E2 cream was effective in rapidly reducing bone turnover in postmenopausal women and in counteracting the accelerated postmenopausal bone loss.

Double-tracer dosimetry of organs in assessment of bone marrow involvement by two monoclonal antibodies

Five patients with ductal breast cancer were studied using simultaneous administration of 99Tcm-labelled BW250/183 and 131I-labelled B72.3 monoclonal antibodies (MAbs). The distribution and dosimetry of these tracers were evaluated using the information from simultaneous anterior and posterior whole body scintigrams, together with 99Tcm and 131I standard activity sources, recorded on an average of 1, 4, 24, 90 and 224 h after injection. A method to eliminate 131I Scatter on 99Tcm-channel was developed. The geometric means of conjugate views and region-of-interest analysis were used to determine organ uptakes, mean residence times and absorbed radiation dose estimates of organs induced by the tracers. Organ uptakes (% of injected activity/ml) varied from 6.2 x 10(-3 /red marrow to 3.1 X 10(-2)/liver for 99Tcm-MAb and from 3.1 x 10(-2)/red marrow to 1.8 x 10(-1)/liver for 131I-MAb, one hour after injection. Calculated average residence times of organs for 99Tcm-labelled BW250/183 were in the range of physical mean-life of 99Tcm and from 71 to 95 h for 131I-B72.3 respectively. The average total absorbed dose from 99Tcm-MAb to the bone marrow was 0.01 and to the spleen 0.14 mGy/MBq and from 131I-MAb the corresponding values were 0.48 and 10.76 mGy/MBq. This double-tracer technique provides information from two antibodies having different kinetic behaviour and may facilitate in distinguishing various antigens in targeting and control MAb applications.