Blood flow measurements with [(15)O]H2O and [18F]fluoride ion PET in porcine vertebrae

Utility of a simplified [18F] sodium fluoride PET imaging method to quantify bone metabolic flux for a wide range of clinical applications

We review the rationale, methodology, and clinical utility of quantitative [18F] sodium fluoride ([18F]NaF) positron emission tomography-computed tomography (PET-CT) imaging to measure bone metabolic flux (Ki, also known as bone plasma clearance), a measurement indicative of the local rate of bone formation at the chosen region of interest. We review the bone remodelling cycle and explain what aspects of bone remodelling are addressed by [18F]NaF PET-CT. We explain how the technique works, what measurements are involved, and what makes [18F]NaF PET-CT a useful tool for the study of bone remodelling. We discuss how these measurements can be simplified without loss of accuracy to make the technique more accessible. Finally, we briefly review some key clinical applications and discuss the potential for future developments. We hope that the simplified method described here will assist in promoting the wider use of the technique.

Emerging Role of 18F-NaF PET/Computed Tomographic Imaging in Osteoporosis: A Potential Upgrade to the Osteoporosis Toolbox

Osteoporosis is a metabolic bone disorder that leads to a decline in bone microarchitecture, predisposing individuals to catastrophic fractures. The current standard of care relies on detecting bone structural change; however, these methods largely miss the complex biologic forces that drive these structural changes and response to treatment. This review introduces sodium fluoride (18F-NaF) positron emission tomography/computed tomography (PET/CT) as a powerful tool to quantify bone metabolism. Here, we discuss the methods of 18F-NaF PET/CT, with a special focus on dynamic scans to quantify parameters relevant to bone health, and how these markers are relevant to osteoporosis.

[18F]Sodium fluoride PET-MRI detects increased metabolic bone response to whole-joint loading stress in osteoarthritic knees

OBJECTIVE

Altered joint function is a hallmark of osteoarthritis (OA). Imaging techniques for joint function are limited, but [18F]sodium fluoride (NaF) PET-MRI may assess the acute joint response to loading stresses. [18F]NaF PET-MRI was used to study the acute joint response to exercise in OA knees, and compare relationships between regions of increased uptake after loading and structural OA progression two years later.

METHODS

In this prospective study, 10 participants with knee OA (59 ± 8 years; 8 female) were scanned twice consecutively using a PET-MR system and performed a one-legged squat exercise between scans. Changes in tracer uptake measures in 9 bone regions were compared between knees that did and did not exercise with a mixed-effects model. Areas of focally large changes in uptake between scans (ROIfocal, ΔSUVmax > 3) were identified and the presence of structural MRI features was noted. Five participants returned two years later to assess structural change on MRI.

RESULTS

There was a significant increase in [18F]NaF uptake in OA exercised knees (SUV P < 0.001, KiP = 0.002, K1P < 0.001) that differed by bone region.

CONCLUSION

There were regional differences in the acute bone metabolic response to exercise and areas of focally large changes in the metabolic bone response that might be representative of whole-joint dysfunction.

[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.

A Short Dynamic Scan Method of Measuring Bone Metabolic Flux Using [18F]NaF PET

[¹⁸F]NaF PET measurements of bone metabolic flux (K_i) are conventionally obtained with 60-min dynamic scans analysed using the Hawkins model. However, long scan times make this method expensive and uncomfortable for subjects. Therefore, we evaluated and compared measurements of K_i with shorter scan times analysed with fixed values of the Hawkins model rate constants. The scans were acquired in a trial in 30 postmenopausal women, half treated with teriparatide (TPT) and half untreated. Sixty-minute PET-CT scans of both hips were acquired at baseline and week 12 after injection with 180 MBq [¹⁸F]NaF. Scans were analysed using the Hawkins model by fitting bone time–activity curves at seven volumes of interest (VOIs) with a semi-population arterial input function. The model was re-run with fixed rate-constants for dynamic scan times from 0–12 min increasing in 4-min steps up to 0–60 min. Using the Hawkins model with fixed rate-constants, K_i measurements with statistical power equivalent or superior to conventionally analysed 60-min dynamic scans were obtained with scan times as short as 12 min.

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.

(2S,4R)-4-[18F]Fluoroglutamine as a PET Indicator for Bone Marrow Metabolism Dysfunctional: from Animal Experiments to Clinical Application

PURPOSE

Previous reports confirmed that (2S,4R)-4-[¹⁸F]Fluoroglutamine ([¹⁸F]GLN) accumulated in bone and bone marrow. This study investigates the potential of using [¹⁸F]GLN positron emission tomography (PET) to monitor changes of bone marrow activity after chemotherapy (myelosuppression).

PROCEDURES

Bone marrow inhibition model in mice was induced by an intravenous injection of chemotherapy drug (doxorubicin or rituximab) and the inhibition was confirmed by routine blood cell counts. Bone uptakes of these four radiotracers (2-deoxy-2-[¹⁸F]fluoro-D-glucose, [¹⁸F]GLN, 3'-dexoy-3'-[¹⁸F]fluorothymidine ([¹⁸F]FLT), and sodium [¹⁸F]fluoride) in the mice were measured after i.v. injection and dissection of femur and tibia, and the uptakes in bone-only (BO) and bone marrow (BM) were obtained after separating bone from bone marrow. Additionally, six volunteers were recruited and evaluated with [¹⁸F]GLN. The PET-/CT-guided volumes of interests (VOI) in cervical, thoracic, lumbar vertebra, and skull cortical bone were defined as bone marrow or bone for evaluation, respectively.

RESULTS

[¹⁸F]GLN showed a relatively high bone marrow uptake in mice (up to 9.5 ± 1.3 % ID/g) at 1 h after injection, which was 2.1 times that of [¹⁸F]FLT. The [¹⁸F]GLN uptakes in the bone marrow were substantially inhibited by chemotherapy drug. The decrease of [¹⁸F]GLN's bone marrow uptake was consistent with the reduction of white blood cells (myelosuppression). For [¹⁸F]GLN/PET imaging in humans, the SUV_mean value of bone marrow (1 h after i.v. injection) was between 3.1 and 3.6 in the healthy volunteers (n = 3), and between 1.8 and 2.2 (n = 3) (P < 0.001) in myelosuppression patients, showing a clear reduction of bone marrow uptake.

CONCLUSIONS

Dissection experiments in mice showed that [¹⁸F]GLN displayed relatively high bone marrow uptake, and the uptake was sensitive to bone marrow inhibition induced by doxorubicin/rituximab. The same conclusion was confirmed [¹⁸F]GLN/PET imaging in humans. Therefore, [¹⁸F]GLN/PET imaging may be a useful tool to assess reduction of bone marrow activity in cancer patients, who may be at risk of myelosuppression after chemotherapy.

TRIAL REGISTRATION

Approved by Institutional Review Board of Peking University Cancer Hospital (No. 2017KT38). Registered 18 August 2017.

Fingerprint pattern of bone mineralisation on cemented and uncemented femoral stems: analysis by [18F]-fluoride-PET in a randomised clinical trial

PURPOSE

We present a randomised clinical study using 18F-fluoride positron emission tomography/computed tomography (F-PET/CT) to analyse the osteoblastic part of bone metabolism (new bone mineralisation) in periprosthetic bone adjacent to femoral stems following total hip arthoplasty (THA) surgery. Patients with hip osteoarthritis were randomly assigned to THA surgery with cemented or uncemented femoral components.

PATIENTS AND METHODS

THA was performed on 26 patients (26 cases) with hip osteoarthritis. The patients received either an uncemented HA-coated femoral stem or a cemented one. The contralateral healthy femur was used as referent for normal bone metabolism. The patients were analysed with clinical score, radiography and F-PET/CT preoperatively, and postoperatively at 6 weeks and 6 months. After 2 years, clinical score and radiography was analysed again. We used the Polar Map system for analysing and presenting the PET results in 13 regions of interest adjacent to the whole stem.

RESULTS

The clinical results were good in all patients; there were no major complications. Radiographically, all stems were stable. PET analyses after 6 weeks showed that bone mineralising activity was significantly higher around the uncemented stems, both compared to the cemented group and to the contralateral healthy reference femur group. The cemented group also had elevated activity but only at a barely significant level.

INTERPRETATION

Mineralising activity analysed with F-PET/CT was significantly higher for the uncemented group and also decreased at a slower rate. F-PET/CT is a useful new tool for analysing secondary stabilisation of femoral stems after THA. The study was registered at ClinicalTrials.gov (identifier NCT01623687).

Inhibition of vascular endothelial growth factor in young adult mice causes low bone blood flow and bone strength with no effect on bone mass in trabecular regions

Objective

To determine the effect of an antibody to vascular endothelial growth factor (VEGF) on bone blood flow, bone strength, and bone mass in the young adult mouse.

Methods

Ten-week-old male BALB/cJ mice were body weight-randomized into either a rodent anti-VEGF monoclonal antibody (anti-VEGF, B20-4.1.1; 5 mg/kg 2×/wk.; n = 12) group or a vehicle (VEH; n = 12) group. After 42 days, mice were evaluated for bone blood flow at the distal femur by ¹⁸F-NaF-PET/CT and then necropsied. Samples from trabecular and cortical bone regions were evaluated for bone strength by mechanical testing, bone mass by peripheral quantitative computed tomography (pQCT), and micoarchitecture (MicroCT). Hydration of the whole femur was studied by proton nuclear magnetic resonance relaxometry (¹H NMR).

Results

Distal femur blood flow was 43% lower in anti-VEGF mice than in VEH mice (p = 0.009). Ultimate load in the lumbar vertebral body was 25% lower in anti-VEGF than in VEH mice (p = 0.013). Bone mineral density (BMD) in the trabecular region of the proximal humeral metaphysis by pQCT, and bone volume fraction and volumetric BMD by MicroCT were the same in the two groups. Volume fraction of bound water (BW) of the whole femur was 14% lower in anti-VEGF than in VEH mice (p = 0.003). Finally, BW, but not cortical tissue mineral density, helped section modulus explain the variance in the ultimate moment experienced by the femur in three-point bending.

Conclusion

Anti-VEGF caused low bone blood flow and bone strength in trabecular bone regions without influencing BMD and microarchitecture. Low bone strength was also associated with low bone hydration. These data suggest that bone blood flow is a novel bone property that affects bone quality.

•

An antibody to vascular endothelial growth factor (anti-VEGF) caused low bone blood flow in a trabecular bone rich region.

•

Anti-VEGF did not affect trabecular bone region and bone hydration of the whole femur were also low, trabecular bone mass was not affected by anti-VEGF.

•

Bone blood flow may be a bone property that affects bone quality through bone hydration.

•

Anti-VEGF caused low trabecular bone strength in the vertebral body and low bone hydration of the whole femur.

18F-fluoride as a prognostic indicator of bone regeneration

Positron emission tomography (PET) is a form of nuclear imaging, which quantitatively assesses the metabolic activity through the uptake of radioactive tracers. ¹⁸F-fluoride is a positron-emitting isotope with high affinity for bone. Despite its potential as a non-invasive measure of bone metabolism, quantitative ¹⁸F-fluoride PET has only been used sparsely in orthopaedic applications. It has been speculated that ¹⁸F-fluoride PET characterizes cellular activity of bone forming cells in the early stages of the regenerative process and therefore precedes the mineralization detected by conventional computed tomography (CT). Our aim was thus to combine in vivo PET and CT to map the spatiotemporal course of bone regeneration during fracture healing using an open femur fracture model in the rat and characterize regeneration in untreated and pharmacologically treated fractures using both imaging modalities. We hypothesized that PET ¹⁸F-fluoride tracer activity at an earlier time point is predictive of CT measured bone formation at a later time point. On the basis of the RMSE and R² metrics of linear regression models it was conceivable for bone volumes to be predicted up to three weeks in advance in a rodent model (RMSE: 14 mm³-18 mm³, R²: 0.79-0.82). Moreover, the data suggested that ¹⁸F-fluoride positron-emitting activity had the potential to separate bone formation from resorption and thus could be of interest across a wide array of orthopaedic applications. Based on this data, we conclude that ¹⁸F-fluoride positron-emitting activity is strongly correlated to bone formation and could potentially predict the volume of bone regenerated at fracture sites. The volume of bone regenerated at a fracture site can be interpreted as a measure of the healing response and ¹⁸F-fluoride should be further investigated as a predictive diagnostic tool to identify if bone fractures will heal successfully or result in delayed healing or non-union. STATEMENT OF SIGNIFICANCE: We aimed to combine in vivo PET and CT imaging to map the spatiotemporal course of bone regeneration during fracture healing using an open femur fracture model in the rat and characterize regeneration in untreated and pharmacologically treated fractures using both imaging modalities. We hypothesized that PET ¹⁸F-fluoride tracer activity at an earlier time point is predictive of CT measured bone formation at a later time point. Our data suggest that ¹⁸F-fluoride positron-emitting activity can separate bone formation from resorption and thus could be of interest across a wide array of orthopaedic applications including as a predictive diagnostic tool to identify if fractures will heal successfully or result in delayed healing or non-union.

ACETABULAR RECONSTRUCTION IN PAPROSKY TYPE III DEFECTS

Objectives

Severe pelvic deficiency presents a difficult problem in hip arthroplasty. Specifically, the goals are to restore the pelvic bone stock, place the acetabular component in the correct anatomical position, and optimize joint stability. Currently, many surgical techniques have been developed for prosthetic revision surgery for acetabular complex defects, but no consensus has been reached on the best treatment. The objective of this study was to review mid-term cases of severe bone defect (Paprosky type III) treated with a bone allograft and ring Bursch-Schneider anti-protrusion cage (BSAC).

Methods

A retrospective consecutive series review of the first 23 complex acetabular reconstructions performed between 2006 and 2011 was conducted. The series included the learning curve of the procedure and a minimum 5-year follow-up.

Conclusion

Our study confirmed the efficacy of using a frozen morselized allograft combined with a metal ring-type BSAC for acetabular reconstruction. The anatomical location of the center of rotation of the hip must be recovered for long-term success. In massive loosening cases, the anatomical center of rotation can only be restored by bone density reconstruction using a graft protected by a ring to improve the centering of the head. Level of Evidence IV, Case Series.

Site specific measurements of bone formation using [18F] sodium fluoride PET/CT

Dynamic positron emission tomography (PET) imaging with fluorine-18 labelled sodium fluoride ([¹⁸F]NaF) allows the quantitative assessment of regional bone formation by measuring the plasma clearance of fluoride to bone at any site in the skeleton. Today, hybrid PET and computed tomography (CT) dual-modality systems (PET/CT) are widely available, and [¹⁸F]NaF PET/CT offers a convenient non-invasive method of studying bone formation at the important osteoporotic fracture sites at the hip and spine, as well as sites of pure cortical or trabecular bone. The technique complements conventional measurements of bone turnover using biochemical markers or bone biopsy as a tool to investigate new therapies for osteoporosis, and has a potential role as an early biomarker of treatment efficacy in clinical trials. This article reviews methods of acquiring and analyzing dynamic [¹⁸F]NaF PET/CT scan data, and outlines a simplified approach combining venous blood sampling with a series of short (3- to 5-minute) static PET/CT scans acquired at different bed positions to estimate [¹⁸F]NaF plasma clearance at multiple sites in the skeleton with just a single injection of tracer.

Blood perfusion in osteomyelitis studied with [15O]water PET in a juvenile porcine model

Background

Osteomyelitis is a serious disease which can be difficult to treat despite properly instituted antibiotic therapy. This appears to be related at least partly to degraded vascularisation in the osteomyelitic (OM) lesions. Studies of perfusion in OM bones are, however, few and not quantitative. Quantitative assessment of perfusion could aid in the selection of therapy. A non-invasive, quantitative way to study perfusion is dynamic [¹⁵O]water positron emission tomography (PET). We aim to demonstrate that the method can be used for measuring perfusion in OM lesions and hypothesize that perfusion will be less elevated in OM lesions than in soft tissue (ST) infection. The study comprised 11 juvenile pigs with haematogenous osteomyelitis induced by injection of Staphylococcus aureus into the right femoral artery 1 week before scanning (in one pig, 2 weeks). The pigs were dynamically PET scanned with [¹⁵O]water to quantify blood perfusion. OM lesions (N = 17) in long bones were studied, using the left limb as reference. ST lesions (N = 8) were studied similarly.

Results

Perfusion was quantitatively determined. Perfusion was elevated by a factor 1.5 in OM lesions and by a factor 6 in ST lesions.

Conclusions

Blood perfusion was successfully determined in pathological subacute OM lesions; average perfusion was increased compared to that in a healthy bone, but as hypothesized, the increase was less than in ST lesions, indicating that the infected bone has less perfusion reserve than the infected soft tissue.

Electronic supplementary material

The online version of this article (doi:10.1186/s13550-016-0251-2) contains supplementary material, which is available to authorized users.

Using PET/CT Bone Scan Dynamic Data to Evaluate Tibia Remodeling When a Taylor Spatial Frame Is Used: Short and Longer Term Differences

Eighteen consecutive patients, treated with a Taylor Spatial Frame for complex tibia conditions, gave their informed consent to undergo Na¹⁸F⁻ PET/CT bone scans. We present a Patlak-like analysis utilizing an approximated blood time-activity curve eliminating the need for blood aliquots. Additionally, standardized uptake values (SUV) derived from dynamic acquisitions were compared to this Patlak-like approach. Spherical volumes of interest (VOIs) were drawn to include broken bone, other (normal) bone, and muscle. The SUV_m(t) (m = max, mean) and a series of slopes were computed as (SUV_m(t_i) − SUV_m(t_j))/(t_i − t_j), for pairs of time values t_i and t_j. A Patlak-like analysis was performed for the same time values by computing ((VOI_p(t_i)/VOI_e(t_i))−(VOI_p(t_j)/VOI_e(t_j)))/(t_i − t_j), where p = broken bone, other bone, and muscle and e = expected activity in a VOI. Paired comparisons between Patlak-like and SUV_m slopes showed good agreement by both linear regression and correlation coefficient analysis (r = 84%, r_s = 78%-SUV_max, r = 92%, and r_s = 91%-SUV_mean), suggesting static scans could substitute for dynamic studies. Patlak-like slope differences of 0.1 min⁻¹ or greater between examinations and SUV_max differences of ~5 usually indicated good remodeling progress, while negative Patlak-like slope differences of −0.06 min⁻¹ usually indicated poor remodeling progress in this cohort.

(18)F-NaF PET/CT: EANM procedure guidelines for bone imaging

The aim of this guideline is to provide minimum standards for the performance and interpretation of (18)F-NaF PET/CT scans. Standard acquisition and interpretation of nuclear imaging modalities will help to provide consistent data acquisition and numeric values between different platforms and institutes and to promote the use of PET/CT modality as an established diagnostic modality in routine clinical practice. This will also improve the value of scientific work and its contribution to evidence-based medicine.

Characterization of bone perfusion by dynamic contrast-enhanced magnetic resonance imaging and positron emission tomography in the Dunkin-Hartley guinea pig model of advanced osteoarthritis

This study characterizes changes in subchondral bone circulation in OA and examines relationships to bone structure and cartilage degeneration in Dunkin-Hartley guinea pigs. We have used dynamic contrast-enhanced MRI (DCE-MRI) and PET, with pharmacokinetic modeling, to characterize subchondral bone perfusion. Assessments are made of perfusion kinetics and vascular permeability by MRI, and blood volume and flow, and radionuclide incorporation into bone, by PET. These parameters are compared to cartilage lesion severity and bone histomorphometry. Assessments of intraosseous thrombi are made morphologically. Prolonged signal enhancement during the clearance phase of MRI correlated with OA severity and suggested venous stasis. Vascular permeability was not increased indicating that transvascular migration of contrast agent was not responsible for signal enhancement. Intraosseous thrombi were not observed. Decreased perfusion associated with severe OA was confirmed by PET and was associated with reduced radionuclide incorporation and osteoporosis. MRI and PET can be used to characterize kinetic parameters of circulation in OA and correlate them with subchondral bone metabolism of interest to the pathophysiology of OA. The significance of these observations may lie in alterations induced in the expression of cytokines by OA osteoblasts that are related to bone remodeling and cartilage breakdown.

Imaging of site specific bone turnover in osteoporosis using positron emission tomography

The functional imaging technique of dynamic fluorine-18 labeled sodium fluoride positron emission tomography ((18)F-NaF PET) allows the quantitative assessment of regional bone formation by measuring the plasma clearance of fluoride to bone at any site in the skeleton. (18)F-NaF PET provides a novel and noninvasive method of studying site-specific bone formation at the hip and spine, as well as areas of pure cortical or trabecular bone. The technique complements conventional measurements of bone turnover using biochemical markers and bone biopsy as a tool to investigate new treatments for osteoporosis, and holds promise of a future role as an early biomarker of treatment efficacy in clinical trials. This article reviews methods of acquiring and analyzing (18)F-NaF PET scan data, and outlines a simplified approach that uses 5-minute static PET scan images combined with venous blood samples to estimate (18)F-NaF plasma clearance at multiple sites in the skeleton with a single injection of tracer.

Quantification of 18F-Fluoride Kinetics: Evaluation of Simplified Methods

(18)F-fluoride PET is a promising noninvasive method for measuring bone metabolism and bone blood flow. The purpose of this study was to assess the performance of various clinically useful simplified methods by comparing them with full kinetic analysis. In addition, the validity of deriving bone blood flow from K1 of (18)F-fluoride was investigated using (15)O-H2O as a reference.

METHODS

Twenty-two adults (mean age ± SD, 44.8 ± 25.2 y), including 16 patients scheduled for bone surgery and 6 healthy volunteers, were studied. All patients underwent dynamic (15)O-H2O and (18)F-fluoride scans before surgery. Ten of these patients had serial PET measurements before and at 2 time points after local bone surgery. During all PET scans, arterial blood was monitored continuously. (18)F-fluoride data were analyzed using nonlinear regression (NLR) and several simplified methods (Patlak and standardized uptake value [SUV]). SUV was evaluated for different time intervals after injection and after normalizing to body weight, lean body mass, and body surface area, and simplified measurements were compared with NLR results. In addition, changes in SUV and Patlak-derived fluoride influx rate (Ki) after surgery were compared with corresponding changes in NLR-derived Ki. Finally, (18)F-fluoride K1 was compared with bone blood flow derived from (15)O-H2O data, using the standard single-tissue-compartment model.

RESULTS

K1 of (18)F-fluoride correlated with measured blood flow, but the correlation coefficient was relatively low (r = 0.35, P < 0.001). NLR resulted in a mean Ki of 0.0160 ± 0.0122, whereas Patlak analysis, for the interval 10-60 min after injection, resulted in an almost-identical mean Ki of 0.0161 ± 0.0117. The Patlak-derived Ki, for 10-60 min after injection, showed a high correlation with the NLR-derived Ki (r = 0.976). The highest correlation between Ki and lean body mass-normalized SUV was found for the interval 50-60 min (r = 0.958). Finally, changes in SUV correlated significantly with those in Ki (r = 0.97).

CONCLUSION

The present data support the use of both Patlak and SUV for assessing fluoride kinetics in humans. However, (18)F-fluoride PET has only limited accuracy in monitoring bone blood flow.

Analysis of bone mineralization on uncemented femoral stems by [18F]-fluoride-PET: a randomized clinical study of 16 hips in 8 patients

PURPOSE

We present the first study using fluoride-positron emission CT (F-PET/CT) to analyze mineralization of bone in the femur adjacent to uncemented stems following total hip arthroplasty (THA). We studied patients who were operated bilaterally for osteoarthritis with 2 different stems during the same surgical session.

PATIENTS AND METHODS

THA was performed bilaterally during the same surgical session in 8 patients with bilateral osteoarthritis of the hip. An SL-PLUS stem was inserted in one hip and a BetaCone stem was inserted in the contralateral hip, with randomization of side and sequence. A second group of 12 individuals with a normal healthy hip was used as reference for normal bone metabolism. Clinical and radiographic evaluation was performed preoperatively, postoperatively, and at 2 years. We used [18F]-fluoride-PET/CT to analyze bone mineralization adjacent to the stems 1 week, 4 months, and 12 months after surgery. We modified the Polar Map system to fit the upper femur for analysis and presentation of the PET results from 12 regions of interest adjacent to the whole stem.

RESULTS

The clinical results were good at 2 years. By radiography, all stems were stable. At PET analyses 1 week after surgery, the activity was higher for the SL-PLUS group than for the BetaCone group. The activity was statistically significantly higher for both stems than the reference values at 4 months, and was most pronounced in the upper femur. At one year, the activity had declined more for the BC group than for the SL group.

INTERPRETATION

The bone mineralization activity varied between different regions for the same stem and between different time periods for each group. F-PET/CT is a novel and valuable tool for analysis of bone mineralization patterns around uncemented femoral stems in detail. The combination of PET/CT analysis and the modified Polar Map system may provide a useful tool for future studies of metabolic bone responses to prosthetic implants.

Age-related changes in pre- and postmenopausal women investigated with 18F-fluoride PET--a preliminary study

OBJECTIVE

To evaluate the relationship between age and regional skeletal uptake at sites consisting of either predominantly trabecular or cortical bone using (18)F-fluoride positron emission tomography (PET) in pre- and postmenopausal women.

MATERIALS AND METHODS

Thirty-two women (40.6 ± 12.3 years; age range 25-72 years) were assigned to one of two groups: group 1 comprised 22 premenopausal women (33 ± 6.5 years; age range 25-48 years) and group 2 comprised 10 postmenopausal women (56 ± 6.7 years; age range 49-72 years). The maximum standardized uptake value (SUVmax) was determined from the lumbar spine and the humeral shaft. Student's t-test for each unpaired dataset was used to evaluate statistical differences between the two groups. The SUVmax values for the humeral shaft and the lumbar spine were compared with aging.

RESULTS

The SUVmax (mean ± SD) was 1.2 ± 0.5 in the humeral shaft and 4.7 ± 1.0 in the lumbar spine. The SUVmax in the humeral shaft correlated significantly with advancing age (r = 0.67, P < 0.01). The SUVmax in the lumbar spine declined significantly with advancing age (r = -0.50, P < 0.01). The humeral shaft of women in group 1 exhibited a significantly lower SUVmax compared to that in group 2 (1.1 ± 0.4 versus 1.6 ± 0.6; P < 0.05). On the other hand, the lumbar spine of women in group 1 exhibited a significantly higher SUVmax compared to that in group 2 (5.1 ± 0.7 versus 4.0 ± 1.1; P < 0.05). The mean SUVmax in the lumbar spine was 2.5 times greater than that in the humeral shaft in group 2.

CONCLUSION

Semiquantitative analysis with (18)F-fluoride PET might be a useful tool for analyzing age-related changes in pre- and postmenopausal women.

Quantitative PET Imaging Using (18)F Sodium Fluoride in the Assessment of Metabolic Bone Diseases and the Monitoring of Their Response to Therapy

Studies of bone remodeling using bone biopsy and biochemical markers of bone turnover measured in serum and urine are important for investigating how new treatments for osteoporosis affect bone metabolism. Positron emission tomography with (18)F sodium fluoride ((18)F NaF PET) for studying bone metabolism complements these conventional methods. Unlike biochemical markers, which measure the integrated response to treatment across the whole skeleton, (18)F NaF PET can distinguish changes occurring at sites of clinically important osteoporotic fractures. Future studies using (18)F NaF PET may illuminate current clinical problems, such as the possible association between long-term treatment with bisphosphonates and atypical fractures of the femur.

Acetabular reconstruction using morselized allograft and a reinforcement ring for revision arthroplasty with Paprosky type II and III bone loss: survival analysis of 95 hips after 5 to 13 years

INTRODUCTION

Treatment of acetabular loosening and accompanying bone defects requires that the bone stock be rebuilt, the primary stability ensured, and the hip center of rotation restored to its anatomical location.

HYPOTHESIS

Acetabular reconstruction using morselized allograft and a reinforcement ring will meet these requirements and ensure medium-term survival.

PATIENTS AND METHODS

A retrospective study was performed on 95 acetabular revision cases (95 patients) performed between 1987 and 1995. The average age at revision was 69.5 years (42 to 86 years). Among these acetabular loosening cases, 12 cases had a type II Paprosky acetabular bone defect and 83 cases had a type III defect.

RESULTS

The average follow-up was 8 years (5 to 13 years). There were seven post-operative dislocations, three deep infections, and two cases of repeated acetabular loosening. The cumulative survival rate at 14 years was 77.9% (95% CI: 61.96% to 93.84%). The average Postel Merle d'Aubigné (PMA) score improved from 8 (range 6-11) preoperatively to 14.8 (range 8-18) at follow-up; the Harris score improved from 35.3 (range 11-52) to 71.1 (range 40-94) (P<0.001). Based on the parameters outlined by Ranawat, the optimal centre of rotation was restored in 45% of cases. Graft integration was found to be good in 60% of cases. The reinforcement ring had migrated in five cases, including two cases of acetabular loosening that required an additional revision. The functional result was better when the hip center of rotation was restored (P<0.05). Conversely, the position of the hip center of rotation had no effect on graft integration or acetabular fixation.

DISCUSSION

This series confirmed that acetabular reconstruction using morselized allograft and a reinforcement ring is effective in the medium term as a treatment for acetabular loosening with severe bone deficiency. It also revealed that restoring the hip center of rotation can improve functional results.

LEVEL OF EVIDENCE

Level IV, retrospective study.

The assessment of regional skeletal metabolism: studies of osteoporosis treatments using quantitative radionuclide imaging

Studies of bone remodeling using bone biopsy and biochemical markers of bone turnover play an important role in research studies to investigate the effect of new osteoporosis treatments on bone quality. Quantitative radionuclide imaging using either positron emission tomography with fluorine-18 sodium fluoride or gamma camera studies with technetium-99m methylene diphosphonate provides a novel tool for studying bone metabolism that complements conventional methods, such as bone turnover markers (BTMs). Unlike BTMs, which measure the integrated response to treatment across the whole skeleton, radionuclide imaging can distinguish the changes occurring at sites of particular clinical interest, such as the spine or proximal femur. Radionuclide imaging can be used to measure either bone uptake or (if done in conjunction with blood sampling) bone plasma clearance. Although the latter is more complicated to perform, unlike bone uptake, it provides a measurement that is specific to the bone metabolic activity at the measurement site. Treatment with risedronate was found to cause a decrease in bone plasma clearance, whereas treatment with the bone anabolic agent teriparatide caused an increase. Studies of teriparatide are of particular interest because the treatment has different effects at different sites in the skeleton, with a substantially greater response in the flat bone of the skull and cortical bone in the femur compared with the lumbar spine. Future studies should include investigations of osteonecrosis of the jaw and atypical fractures of the femur to examine the associated regional changes in bone metabolism and to throw light on the underlying pathologies.

Kinetic analysis of 18F-fluoride PET images of breast cancer bone metastases

The most common site of metastasis for breast cancer is bone. Quantitative (18)F-fluoride PET can estimate the kinetics of fluoride incorporation into bone as a measure of fluoride transport, bone formation, and turnover. The purpose of this analysis was to evaluate the accuracy and precision of (18)F-fluoride model parameter estimates for characterizing regional kinetics in metastases and normal bone in breast cancer patients.

METHODS

Twenty metastatic breast cancer patients underwent dynamic (18)F-fluoride PET. Mean activity concentrations were measured from serial blood samples and regions of interest placed over bone metastases, normal vertebrae, and cardiac blood pools. This study examined parameter identifiability, model sensitivity, error, and accuracy using parametric values from the patient cohort.

RESULTS

Representative time-activity curves and model parameter ranges were obtained from the patient cohort. Model behavior analyses of these data indicated (18)F-fluoride transport and flux (K(1) and Ki, respectively) into metastatic and normal osseous tissue could be independently estimated with a reasonable bias of 9% or less and reasonable precision (coefficients of variation <or= 16%). Average (18)F-fluoride transport and flux into metastases from 20 patients (K(1) = 0.17 +/- 0.08 mL x cm(-3) x min(-1) and Ki = 0.10 +/- 0.05 mL x cm(-3) x min(-1)) were both significantly higher than for normal bone (K(1) = 0.09 +/- 0.03 mL x cm(-3) x min(-1) and Ki = 0.05 +/- 0.02 mL x cm(-3) x min(-1), P < 0.001).

CONCLUSION

Fluoride transport and flux can be accurately and independently estimated for bone metastases and normal vertebrae. Reasonable bias and precision for estimates of K(1) and Ki from simulations and significant differences in values from patient modeling results in metastases and normal bone suggest that (18)F-fluoride PET images may be useful for assessing changes in bone turnover in response to therapy. Future studies will examine the correlation of parameters to biologic features of bone metastases and to response to therapy.

Bone healing of severe acetabular defects after revision arthroplasty

BACKGROUND AND PURPOSE

Healing of acetabular bone grafts may be difficult to assess in conventional radiographs. We used PET to analyze healing of morselized bone allografts, impacted in large osteolytic acetabular defects at revision arthroplasty.

PATIENTS AND METHODS

7 cases had a cup revision because of loosening, with repair of a segmental defect using a perforated, wide and thin plate. The osteolytic acetabulum was impacted with morselized bone allograft before cementing a polyethylene cup. [(18)F]-fluoride PET scans were used to monitor bone healing inside the graft bed 1 week, 4 weeks, and 12 months after surgery. The contralateral pelvic bone above the acetabulum was used as reference. A second group of 4 cases was analyzed for bone-forming activity in the state of mechanical loosening of an acetabular component of a THA.

RESULTS

Preoperatively, the uptake was raised by 64% compared to the reference. 1 week after surgery it was increased by 77% in segmental regions, while the uptake was at the reference level in cavitary regions. After 4 months the uptake was increased by 91% in cavitary regions and by 117% in segmental regions. 1 year after surgery, the increase in uptake was 20% in both regions. All implants were stable on radiographs.

INTERPRETATION

We found PET to be a sensitive and useful method for evaluation of the spatial and temporal development of bone formation.

Assessment of the metabolic activity of bone grafts with (18)F-fluoride PET

PURPOSE

The aims of this prospective study were to evaluate quantitative approaches to (18)F-fluoride positron emission tomography (PET) imaging in allogenic bone grafts of the limbs, and to assess the time course of graft healing after surgery.

METHODS

We performed a total of 52 dynamic (18)F-fluoride PET studies in 34 patients with cancellous and full bone grafts. Seven patients were imaged three times at 6, 12, and 24 months after surgery, and four patients were imaged twice. PET data were quantitatively analyzed using non-linear regression (NLR) analysis, Patlak analysis, and standardized uptake value (SUV).

RESULTS

Fluoride bone metabolism in cancellous grafts decreased by 25% from 6 to 12 months post surgery, and revealed a total decrease of 60-65% after 2 years for SUV, K(Pat), and K(NLR). Full bone grafts first showed an increase by 20% from 6 to 12 months and from then on decreased to 70% of the initial activity at the end of 2 years with either quantification method. In two patients with non-union of their full bone grafts, increases in SUV, K(Pat), K(NLR), and K(1) far above average and outside the normal time pattern were observed. Highly significant correlations were found between SUV, K(Pat), K(NLR), and K(1) for both grafts and normal limb bones. In patients imaged repeatedly, the percentage changes in fluoride graft metabolism were also significantly correlated between SUV, K(Pat), and K(NLR).

CONCLUSION

Quantitative (18)F-fluoride PET is a promising tool for assessment of fluoride metabolism and normal healing in bone grafts of the limbs.

Rapid bone and blood flow formation in impacted morselized allografts: positron emission tomography (PET) studies on allografts in 5 femoral component revisions of total hip arthroplasty

5 patients were revised with impaction of morselized frozen allograft and a cemented total hip arthroplasty (THA) because of loosening and osteolysis of a primary hip arthroplasty. Plain film radiographs of the stems showed stable implants in all patients 15-24 months after surgery. The clinical results were good. We used: 1) Positron Emission Tomography (PET) to evaluate vascularization and new bone formation in the allograft, 2) kinetic [18F]-fluoride PET to produce quantitative images, interpreted as new bone formation in the allograft surrounding the femur stem, 3) [15O]-water PET to quantify bone blood flow, and 4) [15O]-carbon monoxide to determine blood volume. After surgery, all patients were evaluated twice: at 1-8 days and 12 months and 3 patients were also studied at 4 months. As early as at 8 days after surgery, blood flow and bone formation had increased greatly adjacent to the allograft. At 4 months blood flow and bone formation were about the same, but activity was highest in the graft material. At 1 year after surgery, blood flow had declined to the levels of the contralateral femur diaphysis in most of the graft bed. These findings using the PET technique showed that angiogenesis and new bone formation occurred early after impaction of morselized bone allografts around the femoral component in revision THA. We found that PET is a sensitive method for evaluating neovascularization and bone formation in the graft beds.

A prospective study of risedronate on regional bone metabolism and blood flow at the lumbar spine measured by 18F-fluoride positron emission tomography

The effect of risedronate on bone metabolism at the lumbar spine was assessed in 18 women who had a 18F-fluoride PET scan at baseline and after 6 months of therapy. The net plasma clearance of fluoride to bone mineral reflecting osteoblastic activity decreased significantly after therapy.

INTRODUCTION

Quantitative radionuclide studies of bone reflect bone blood flow and regional osteoblastic activity, and the latter should change after treatment with a bisphosphonate, although this has not been previously demonstrated. The aim of this study was to examine regional 18F-fluoride kinetics in the lumbar spine measured by 18F-fluoride positron emission tomography (PET) before and after treatment with risedronate.

MATERIALS AND METHODS

Eighteen women, with a mean age of 67.0 years and a T-score of less than -2 at the spine or hip, had a dynamic PET scan of the lumbar spine after the injection of 90 MBq 18F-fluoride ion at baseline and 6 months after commencing risedronate therapy. The arterial plasma input function was derived using aorta arterial activity from the PET image. Time-activity curves were measured by placing regions of interest over the lumbar vertebrae. A three-compartmental model was used to calculate bone blood flow (K(1)) and the net plasma clearance of tracer to bone mineral (K(i)). Rate constants k(2), k(3), and k(4), which describe transport between plasma, the extracellular fluid (ECF) compartment, and the bone mineral compartment, respectively, were also measured.

RESULTS

Mean vertebral K(i) decreased significantly by 18.4% from baseline (3.32 x 10(-2) ml/min/ml) to 6 months post-treatment (2.71 x 10(-2) ml/min/ml; p = 0.04). This decrease was similar in magnitude to the decrease observed for bone-specific alkaline phosphatase, a marker of bone formation. There was no significant difference in K(1) from baseline (1.49 x 10(-1) ml/min/ml) to 6 months after treatment (1.38 x 10(-1) ml/min/ml; p > 0.05). There was a significant increase in k(2), reflecting the reverse transport of fluoride from the extravascular tissue compartment to plasma, after 6 months of treatment (2.90 x 10(-1)/min versus 4.43 x 10(-1)/min; p = 0.01). No significant changes were seen for k(3) or k(4). There was a significant decrease from baseline in the fraction of tracer in the extravascular tissue space that underwent specific binding to the bone matrix (k(3)/[k(2) + k(3)]), decreasing by 18.1% (p = 0.02).

CONCLUSION

K(i), the net plasma clearance to bone mineral reflecting regional osteoblastic activity, displayed a significant decrease after 6 months of antiresorptive therapy. This is the first study to show a direct metabolic effect of antiresorptive therapy on skeletal kinetics at the clinically important site of the lumbar spine. The use of 18F-fluoride PET may provide a useful noninvasive tool to assess novel treatments currently being developed for osteoporosis.

Quantification of skeletal kinetic indices in Paget's disease using dynamic 18F-fluoride positron emission tomography

The purpose of this study was to quantify indices of regional bone metabolism in Paget's disease and to compare these indices with normal bone using dynamic 18F-fluoride positron emission tomography (PET). Seven patients with vertebral Paget's disease had 1 h dynamic 18F-fluoride PET scans performed. The scans included a diseased vertebra and an adjacent normal vertebra. Arterial plasma input functions were also measured. A three-compartment, four-parameter model was used with nonlinear regression analysis to estimate bone kinetic variables. Compared with normal bone, pagetic bone demonstrated higher values of plasma clearance to bone mineral (Ki; 1.03 x 10(-1) vs. 0.36 x 10(-1) ml/min per milliliter; p = 0.018) and clearance to total bone tissue (K1; 2.38 x 10(-1) vs. 1.25 x 10(-1) ml/min per milliliter; p = 0.018), reflecting increased mineralization and blood flow, respectively. Release of 18F-fluoride from bone mineral (k4) was lower in pagetic bone (p = 0.022), suggesting tighter binding of 18F-fluoride to bone mineral. The notional volume of the extravascular bone compartment (K1/k2) was greater in pagetic bone (p = 0.018). Although the unidirectional extraction efficiency from the extravascular space to bone mineral (Ki/K1) was greater in pagetic bone (p = 0.018), a lower pagetic value of k2 (p = 0.028), describing the rate of transfer from the bone extravascular compartment to plasma, suggests that the 18F-fluoride that enters the relatively fibrotic marrow space of pagetic bone may be less accessible for return to plasma. These findings confirm some of the known pathophysiology of Paget's disease, introduce some new observations, and show how dynamic 18F-fluoride PET may be of value in the measurement of regional metabolic parameters in focal bone disorders.

Quantitative studies of bone using (18)F-fluoride and (99m)Tc-methylene diphosphonate: evaluation of renal and whole-blood kinetics

We report a study of the renal and whole-blood kinetics of (18)F-fluoride and (99m)Tc-methylene diphosphonate ((99m)Tc-MDP) and their effect on the evaluation of the skeletal kinetics of the two bone tracers. Data were obtained during an investigation of postmenopausal women taking hormone replacement therapy who were compared with untreated, age-matched controls. After intravenous injection of 18F-fluoride (1 MBq), (99m)Tc-MDP (1 MBq), (51)Cr-ethylenediaminetetraacetic acid (51Cr-EDTA) (3 MBq) and (125)I-human serum albumin ((125)I-HSA) (0.25 MBq), multiple blood samples and urine collections were taken between 0 and 4 h after injection. (51)Cr-EDTA data were used to evaluate the glomerular filtration rate (GFR) and the completeness of each timed urine collection. (125)I-HSA data were used to evaluate the plasma volume and the red cell uptake of the other three tracers. At 4 h, the cumulative urine excretions (and standard deviations, SDs) were: (99m)Tc-MDP, 58.2% (4.8%); (18)F-fluoride, 36.1% (5.7%); (51)Cr-EDTA, 81.5% (4.5%). Plots of the renal clearance of (18)F-fluoride against urine volume showed that urine flow rates greater than 5 ml.min-1 were necessary to ensure a constant renal clearance of (18)F and hence stable conditions for the evaluation of bone tracer kinetics. In contrast, a low urine flow rate had no effect on the renal kinetics of (99m)Tc-MDP. For MDP, the evaluation of skeletal kinetics requires data on protein binding so that calculations can be performed for free MDP. In the present study, protein binding of MDP was evaluated from the ratio of total (99m)Tc-MDP renal clearance to GFR based on the principle that free (99m)Tc-MDP is a GFR tracer. Between 0 and 4 h after injection, the fractional protein binding of MDP increased linearly with time, changing from 21+/-5% immediately after injection to 58+/-5% at 4 h. Although red cell uptake of (99m)Tc-MDP was negligible, for (18)F-fluoride around 30% of circulating tracer was transported in red cells. In view of the data showing the rapid transport of (18)F-fluoride across the red cell membrane, bone kinetic data for (18)F are more accurately reported as whole-blood clearance rather than plasma clearance.

Allogeneic cancellous bone graft and a Burch-Schneider ring for acetabular reconstruction in revision hip arthroplasty

BACKGROUND

There is an ever-increasing number of failed hip arthroplasties associated with massive deficiency of acetabular bone stock consisting of a segmental or cavitary defect. This study was undertaken to evaluate the long-term results after use of morselized cryopreserved allogeneic bone graft and an antiprotrusio cage to treat such a deficiency.

METHODS

From January 1, 1988, to January 1, 1994, forty-one patients (forty-one hips) with an acetabular defect classified as type IIl or IV according to the American Academy of Orthopaedic Surgeons system were operated on with use of a Burch-Schneider ring and morselized cryopreserved allogeneic cancellous bone graft. Thirty-eight patients (thirty-eight hips) were available for clinical and radiographic follow-up examinations at an average of 7.3 years (range, 4.2 to 9.4 years) after surgery.

RESULTS

All measured clinical parameters had improved significantly by the time of the follow-up examination (p < 0.0001). Radiographs confirmed that none of the thirty-eight hips had any measurable migration or displacement of the acetabular component and that osseous consolidation occurred only within the grafted area in all patients.

CONCLUSION

Acetabular reconstruction with use of morselized cryopreserved allogeneic cancellous bone graft and the Burch-Schneider ring can be highly successful in managing massive acetabular deficiencies in revision hip arthroplasty.

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.

Vertebral blood flow and bone mineral density during long-term corticosteroid treatment: An experimental study in immature pigs

STUDY DESIGN

Bone mineral density and regional blood flow were measured in pigs during long-term methylprednisolone treatment.

OBJECTIVES

To investigate possible changes in bone mineral density and vertebral blood flow during long-term glucocorticoid treatment.

SUMMARY OF BACKGROUND DATA

Steroid-induced vertebral osteonecrosis preferentially involves endplates and adjacent cancellous bone. The precise etiology of vertebral osteonecrosis during long-term glucocorticoid treatment is unknown.

METHODS

Twenty-four 10-week-old female Danish landrace sister pigs from 12 litters were treated in two groups. Twelve animals received oral methylprednisolone for 3 months at a daily dose of 100 mg. The 12 sister pigs received no steroid treatment and served as controls. Regional blood blow was measured by means of microspheres in predefined regions of the C6, T11, and L6 vertebrae. In vitro DEXA scanning of the L2-L4 vertebra was performed to assess bone mineral density.

RESULTS

Vertebral cancellous bone and endplate regional blood flow were decreased in the C6 and L6 vertebrae among corticosteroid-treated pigs compared with that of controls.- Width-adjusted lumbar vertebral bone mineral density (g/cm3) was unchanged, whereas projectional lumbar vertebral bone mineral density (g/cm2) was decreased in corticosteroid-treated pigs.

CONCLUSIONS

Long-term methylprednisolone treatment decreases vertebral bone blood flow mainly in cancellous bone and endplates. This may be an important factor in the pathogenesis of osteonecrosis secondary to glucocorticoid treatment. Lumbar vertebral bone mineral density was unchanged in growing pigs on long-term glucocorticoid treatment when expressed as volumetric bone density. The effect of glucocorticoid treatment on vertebral bone mineral density appears to depend on whether it is expressed as projectional (g/cm2) or volumetric bone mineral density (g/cm3). Vertebral and longbone growth was reduced during methylprednisolone treatment.

Differences in skeletal kinetics between vertebral and humeral bone measured by 18F-fluoride positron emission tomography in postmenopausal women

We have sought to investigate regional differences in skeletal kinetics between lumbar vertebrae and the humerus of postmenopausal women with 18F-fluoride positron emission tomography (PET). Twenty-six women, mean age 62 years, had dynamic PET scans of the lumbar spine and lower humerus after the injection of 180 MBq 18F-fluoride ion. Plasma arterial input functions (IFs) were calculated from a mean IF measured arterially from 10 women and scaled according to late individual venous activity. Vertebral and humeral time activity curves were measured by placing regions of interest (ROI) over lumbar vertebrae and the humeral shaft. Using a three-compartmental model and nonlinear regression analysis the macroconstant Ki, representing plasma clearance of fluoride to bone mineral, and the individual rate constants K1 (related to regional skeletal blood flow) and k2 to k4 describing transport between plasma, an extracellular fluid compartment and a bone mineral compartment, were measured. Mean vertebral Ki (3.47x10(-2) ml x min(-1) x ml(-1)) and K1 (1.08x10(-1) ml x min(-1) x ml(-1)) were found to be significantly greater than humeral Ki (1.64x10(-2) ml min(-1) ml(-1); P<0.0001) and K1 (3.90x10(-2) ml x min(-1) x ml(-1); P<0.0001) but no significant differences were found in k2, k3, and k4. These findings confirm differences in regional skeletal kinetics between lumbar vertebrae and the lower humerus. These observations may help increase our understanding of the regional differences in pathophysiology and response to treatment that have been observed in sites consisting predominantly of either trabecular or cortical bone. 18F-fluoride PET may prove to be a valuable technique in the noninvasive measurement of regional skeletal metabolism.