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

Imaging of Bone Metastases in Breast Cancer

Bone metastases are a common site of spread in advanced breast cancer and responsible for morbidity and high health care costs. Imaging contributes to staging and response assessment of the skeleton and has been instrumental in guiding patient management for several decades. Historically this has been with radiographs, computed tomography and bone scans. More recently, molecular and hybrid imaging methods have undergone significant development, including the addition of single photon emission computed tomography/computed tomography to the bone scan, positron emission tomography, with bone-specific and tumor-specific tracers, and magnetic resonance imaging with complementary functional diffusion-weighted imaging. These have allowed different aspects of the abnormal biology associated with bone metastases to be explored. There is ability to interrogate the bone microenvironment with bone-specific tracers and cancer cell characteristics with tumor-specific methods that complement morphological appearances on computed tomography or magnetic resonance imaging. Alongside the advent of novel, more effective and nuanced therapies for bone metastases in breast cancer, there is accumulating evidence that the developments in imaging allow more sensitive and specific detection of bone metastases as well as more accurate and earlier assessment of treatment response leading to improvements in patient management.

Molecular Imaging of Bone Metastases and Their Response to Therapy

Bone metastases are common, especially in more prevalent malignancies such as breast and prostate cancer. They cause significant morbidity and draw on health-care resources. Molecular and hybrid imaging techniques, including SPECT/CT, PET/CT, and whole-body MRI with diffusion-weighted imaging, have improved diagnostic accuracy in staging the skeleton compared with previous standard imaging methods, allowing earlier tailored treatment. With the introduction of several effective treatment options, it is now even more important to detect and monitor response in bone metastases accurately. Conventional imaging, including radiographs, CT, MRI, and bone scintigraphy, are recognized as being insensitive and nonspecific for response monitoring in a clinically relevant time frame. Early reports of molecular and hybrid imaging techniques, as well as whole-body MRI, promise an earlier and more accurate prediction of response versus nonresponse but have yet to be adopted routinely in clinical practice. We summarize the role of new molecular and hybrid imaging methods, including SPECT/CT, PET/CT, and whole-body MRI. These modalities are associated with improvements in diagnostic accuracy for the staging and response assessment of skeletal metastases over standard imaging methods, being able to quantify biologic processes related to the bone microenvironment as well as tumor cells. The described improvements in the imaging of bone metastases and their response to therapy have led to adoption of some of these methods into routine clinical practice in some centers. These methods also provide a better way to assess the treatment response of bone metastases in clinical trials.

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 (SUV_max) 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 SUV_max of the SIJs and SUV_max 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 SUV_max 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 SUV_max 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 SUV_max 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.

Structural and practical identifiability of dual-input kinetic modeling in dynamic PET of liver inflammation

Dynamic 18F-FDG PET with tracer kinetic modeling has the potential to noninvasively evaluate human liver inflammation using the FDG blood-to-tissue transport rate K 1. Accurate kinetic modeling of dynamic liver PET data and K 1 quantification requires the knowledge of dual-blood input function from the hepatic artery and portal vein. While the arterial input function can be derived from the aortic region on dynamic PET images, it is difficult to extract the portal vein input function accurately from PET images. The optimization-derived dual-input kinetic modeling approach has been proposed to overcome this problem by jointly estimating the portal vein input function and FDG tracer kinetics from time activity curve fitting. In this paper, we further characterize the model properties by analyzing the structural identifiability of the model parameters using the Laplace transform and practical identifiability using computer simulation based on fourteen patient datasets. The theoretical analysis has indicated that all the kinetic parameters of the dual-input kinetic model are structurally identifiable, though subject to local solutions. The computer simulation results have shown that FDG K 1 can be estimated reliably in the whole-liver region of interest with reasonable bias, standard deviation, and high correlation between estimated and original values, indicating of practical identifiability of K 1. The result has also demonstrated the correlation between K 1 and histological liver inflammation scores is reliable. FDG K 1 quantification by the optimization-derived dual-input kinetic model is promising for assessing liver inflammation.

Does Measurement of First-Order and Heterogeneity Parameters Improve Response Assessment of Bone Metastases in Breast Cancer Compared to SUVmax in [18F]fluoride and [18F]FDG PET?

PURPOSE

To establish whether first-order statistical features from [18F]fluoride and 2-deoxy-2-[18F] fluoro-D-glucose ([18F]FDG) positron emission tomography/x-ray computed tomography (PET/CT) demonstrate incremental value in skeletal metastasis response assessment compared with maximum standardised uptake value (SUVmax).

PROCEDURES

Sixteen patients starting endocrine treatment for de novo or progressive breast cancer bone metastases were prospectively recruited to undergo [18F]fluoride and [18F]FDG PET/CT scans before and 8 weeks after treatment. Percentage changes in SUV parameters, metabolic tumour volume (MTV), total lesion metabolism (TLM), standard deviation (SD), entropy, uniformity and absolute changes in kurtosis and skewness, from the same ≤ 5 index lesions, were measured. Clinical response to 24 weeks, assessed by two experienced oncologists blinded to PET/CT imaging findings, was used as a reference standard and associations were made between parameters and progression free and overall survival.

RESULTS

[18F]fluoride PET/CT: In four patients (20 lesions) with progressive disease (PD), TLM and kurtosis predicted PD better than SUVmax on a patient basis (4, 4 and 3 out of 4, respectively) and TLM, entropy, uniformity and skewness on a lesion basis (18, 16, 16, 18 and 15 out of 20, respectively). Kurtosis was independently associated with PFS (p = 0.033) and OS (p = 0.008) on Kaplan-Meier analysis. [18F]FDG PET: No parameter provided incremental value over SUVmax in predicting PD or non-PD. TLM was significantly associated with OS (p = 0.041) and skewness with PFS (p = 0.005). Interlesional heterogeneity of response was seen in 11/16 and 8/16 patients on [18F]fluoride and [18F]FDG PET/CT, respectively.

CONCLUSION

With [18F]fluoride PET/CT, some first-order features, including those that take into account lesion volume but also some heterogeneity parameters, provide incremental value over SUVmax in predicting clinical response and survival in breast cancer patients with bone metastases treated with endocrine therapy. With [18F]FDG PET/CT, no first-order parameters were more accurate than SUVmax although TLM and skewness were associated with OS and PFS, respectively. Intra-patient heterogeneity of response occurs commonly between metastases with both tracers and most parameters.

Prediction of therapy response in bone-predominant metastatic breast cancer: comparison of [18F] fluorodeoxyglucose and [18F]-fluoride PET/CT with whole-body MRI with diffusion-weighted imaging

PURPOSE

To compare [18F]-fluorodeoxyglucose (FDG) and [18F]-sodium fluoride (NaF) positron emission tomography/computed tomography (PET/CT) with whole-body magnetic resonance with diffusion-weighted imaging (WB-MRI), for endocrine therapy response prediction at 8 weeks in bone-predominant metastatic breast cancer.

PATIENTS AND METHODS

Thirty-one patients scheduled for endocrine therapy had up to five bone metastases measured [FDG, NaF PET/CT: maximum standardized uptake value (SUVmax); WB-MRI: median apparent diffusion coefficient (ADCmed)] at baseline and 8 weeks. To detect the flare phenomenon, a 12-week NaF PET/CT was also performed if 8-week SUVmax increased. A 25% parameter change differentiated imaging progressive disease (PD) from non-PD and was compared to a 24-week clinical reference standard and progression-free survival (PFS).

RESULTS

Twenty-two patients (median age, 58.6 years, range, 40-79 years) completing baseline and 8-week imaging were included in the final analysis. Per-patient % change in NaF SUVmax predicted 24-week clinical PD with sensitivity, specificity and accuracy of 60, 73.3, and 70%, respectively. For FDG SUVmax the results were 0, 100, and 76.2% and for ADCmed, 0, 100 and 72.2%, respectively. PFS < 24 weeks was associated with % change in SUVmax (NaF: 41.7 vs. 0.7%, p = 0.039; FDG: - 4.8 vs. - 28.6%, p = 0.005) but not ADCmed (- 0.5 vs. 10.1%, p = 0.098). Interlesional response heterogeneity occurred in all modalities and NaF flare occurred in seven patients.

CONCLUSIONS

FDG PET/CT and WB-MRI best predicted clinical non-PD and both FDG and NaF PET/CT predicted PFS < 24 weeks. Lesional response heterogeneity occurs with all modalities and flare is common with NaF PET/CT.

Is Response Assessment of Breast Cancer Bone Metastases Better with Measurement of 18F-Fluoride Metabolic Flux Than with Measurement of 18F-Fluoride PET/CT SUV?

Our purpose was to establish whether noninvasive measurement of changes in 18F-fluoride metabolic flux to bone mineral (Ki) by PET/CT can provide incremental value in response assessment of bone metastases in breast cancer compared with SUVmax and SUVmeanMethods: Twelve breast cancer patients starting endocrine treatment for de novo or progressive bone metastases were included. Static 18F-fluoride PET/CT scans were acquired 60 min after injection, before and 8 wk after commencing treatment. Venous blood samples were taken at 55 and 85 min after injection to measure plasma 18F-fluoride activity concentrations, and Ki in individual bone metastases was calculated using a previously validated method. Percentage changes in Ki, SUVmax, and SUVmean were calculated from the same index lesions (≤5 lesions) from each patient. Clinical response up to 24 wk, assessed in consensus by 2 experienced oncologists masked to PET imaging findings, was used as a reference standard. Results: Of the 4 patients with clinically progressive disease (PD), mean Ki significantly increased (>25%) in all, SUVmax in 3, and SUVmean in 2. Of the 8 non-PD patients, Ki decreased or remained stable in 7, SUVmax in 5, and SUVmean in 6. A significant mean percentage increase from baseline for Ki, compared with SUVmax and SUVmean, occurred in the 4 patients with PD (89.7% vs. 41.8% and 43.5%, respectively; P < 0.001). Conclusion: After 8 wk of endocrine treatment for bone-predominant metastatic breast cancer, Ki more reliably differentiated PD from non-PD than did SUVmax and SUVmean, probably because measurement of SUV underestimates fluoride clearance by not considering changes in input function.

Nuclear Medicine Imaging Techniques for Detection of Skeletal Metastases in Breast Cancer

Bone is the most common site of metastases from advanced breast cancer. Whole-body bone scintigraphy has been most frequently used in the process of managing cancer patients; its advantage is that it provides rapid whole-body imaging for screening of osteoblastic or sclerotic/mixed bone metastases at reasonable cost. Recent advanced techniques, such as single-photon emission computed tomography (SPECT)/CT, quantitative analysis, and bone scan index, contribute to better understanding of the disease state. More recent advances in machines and PET drugs improve the staging of the skeleton with higher sensitivity and specificity.

Comparison of the Variability of SUV Normalized by Skeletal Volume with the Variability of SUV Normalized by Body Weight in 18F-Fluoride PET/CT

Our objective was to test the hypothesis that variability in SUV normalized by skeletal volume (SV) in ¹⁸F-fluoride (¹⁸F-NaF) PET/CT studies is lower than variability in SUV normalized by body weight (BW). Methods: The mean SUV (SUV_mean) was obtained for whole skeletal volume of interest (wsVOI) in 163 selected ¹⁸F-NaF PET/CT studies. These studies were performed to investigate bone metastases and were considered to have normal results. SUV_mean was calculated with normalization by BW (BW SUV_mean), with normalization by SV (SV SUV_mean), and without normalization (WN SUV_mean). The total SV for each patient was also estimated on the basis of the wsVOI defined on the CT component of the PET/CT study. SUV_mean variability for each patient was estimated as the absolute value of the difference between the SUV_mean for the patient and the mean of the SUV_mean for the whole group of patients, divided by the mean of the SUV_mean for the whole group of patients. The variabilities of SUV_mean calculated by the 3 methods were compared using a paired 1-tailed Wilcoxon test. Results: The mean variability for the BW, SV, and WN SUV_mean was 0.16, 0.13, and 0.16, respectively. There were statistically significant differences between SV and BW SUV_mean variability (P = 0.03) and between SV and WN SUV_mean variability (P < 0.01). There was no statistically significant difference between BW and WN SUV_mean variability (P = 0.4). Conclusion: In patients with normal ¹⁸F-NaF PET/CT results, SV SUV_mean presents lower variability than BW SUV_mean.

Bone and Calcified Soft Tissue Metastases of Medullary Thyroid Carcinoma Better Characterized on 18F-Fluoride PET/CT than on 68Ga-Dotatate PET/CT

Herein, we report a case of a 19-year-old man with multiple endocrine neoplasia type 2B (MEN2B) and medullary thyroid carcinoma (MTC) diagnosed when he was 12 years of age. The patient had previously undergone total thyroidectomy, cervical radiotherapy, and chemotherapy. He progressed with known bone, pulmonary, and lymph node metastases and was scanned with ¹⁸F-fluoride (¹⁸F-NaF) and ⁶⁸Ga-dotatate whole-body positron emission tomography/computed tomography (PET/CT) for metastatic disease monitoring. We found that the MTC bone metastases and soft tissue calcified metastases were better characterized on ¹⁸F-NaF PET/CT than on ⁶⁸Ga-dotatate PET/CT. This case illustrates that the ¹⁸F-NaF PET/CT could be helpful not only to the detection of bone metastases but also to the detection of calcified soft tissue metastases in patients with MTC.

Functional and Hybrid Imaging of Bone Metastases

Bone metastases are common, cause significant morbidity, and impact on healthcare resources. Although radiography, computed tomography (CT), magnetic resonance imaging (MRI), and bone scintigraphy have frequently been used for staging the skeleton, these methods are insensitive and nonspecific for monitoring treatment response in a clinically relevant time frame. We summarize several recent reports on new functional and hybrid imaging methods including single photon emission CT/CT, positron emission tomography/CT, and whole-body MRI with diffusion-weighted imaging. These modalities generally show improvements in diagnostic accuracy for staging and response assessment over standard imaging methods, with the ability to quantify biological processes related to the bone microenvironment as well as tumor cells. As some of these methods are now being adopted into routine clinical practice and clinical trials, further evaluation with comparative studies is required to guide optimal and cost-effective clinical management of patients with skeletal metastases. © 2018 American Society for Bone and Mineral Research.

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.

SUV Normalized by Skeletal Volume on 18F-Fluoride PET/CT Studies

OBJECTIVE

To propose a technique for SUV normalization on F-fluoride PET/CT (F-NaF) studies based on skeletal volume and to compare the SUVs normalized by this technique with the ones normalized by body weight.

METHODS

SUVs were obtained in volumes of interest (VOIs) in proximal diaphyseal regions of the right humerus (HD) and right femur (FD) in 12 selected F-NaF studies. The 12 studies presented both regions considered normal by visual examination on PET and CT and were performed in patients presenting body weight below 50 kg (B50) or above 90 kg (A90) (6 patients in each group). The maximum SUVs were calculated in these 2 bone regions in both groups of patients using body weight (SUV BW) and skeletal volume (SUV SV) methodologies. The total skeletal volume for each patient was estimated based on whole skeletal VOIs automatically defined on the CT component of the PET/CT study. The maximum SUVs calculated using the 2 methodologies were compared.

RESULTS

The maximum SUVs BW were statistically higher in the group A90 in both regions, with a P < 0.001 and P < 0.008 for FD and HD, respectively. The maximum SUVs SV in the 2 regions were not statistically different between the groups B50 and A90, P values of 0.27 and 0.87 for FD and HD, respectively.

CONCLUSIONS

The SUVs normalized by skeletal volume present similar results in groups of patients with extremes of body weight. Therefore, this methodology could be more adequate than the one normalized by body weight to semiquantitatively analyze F-NaF studies.

Optimizing an 18F-NaF and 18F-FDG cocktail for PET assessment of metastatic castration-resistant prostate cancer

BACKGROUND

PET/computed tomography (CT) imaging with the sodium-(F)-fluoride/2-(F)-fluoro-2-deoxy-D-glucose (F-NaF/F-FDG) cocktail has been proposed for patients with osseous metastases. This work aimed to optimize the cocktail composition for patients with metastatic castration-resistant prostate cancer (mCRPC).

MATERIALS AND METHODS

The study was carried out on six patients with mCRPC, with a total of 26 analyzed lesions. The patients were injected with F-NaF and F-FDG at separate time points. Dynamic PET/CT imaging recorded the uptake time course for both the tracers into osseous metastases. F-NaF and F-FDG uptakes were decoupled by kinetic analysis, which enabled calculation of F-NaF and F-FDG standardized uptake values (SUVs) images. Peak, mean, and total SUVs were evaluated for both tracers and all visible lesions. The F-NaF/F-FDG cocktail was optimized under the assumption that the contribution of both tracers to image formation is equal. SUV images from PET/CT imaging with a combination of F-NaF and F-FDG were generated for cocktail compositions with an F-NaF : F-FDG ratio varying from 1 : 8 to 1 : 2.

RESULTS

The F-NaF peak and mean SUVs were on average four to five times higher than the F-FDG peak and mean SUVs, with an interlesion coefficient of variations of 20%. The total SUV for F-NaF was on average seven times higher than that for F-FDG. When the F-NaF : F-FDG ratio changed from 1 : 8 to 1 : 2, the typical SUV on the generated PET images increased by 50%, whereas the change in the uptake visual pattern was hardly noticeable.

CONCLUSION

F-NaF and F-FDG in the cocktail contribute equally to image formation when the F-NaF : F-FDG ratio is 1 : 5. Therefore, we propose this ratio as the optimal cocktail composition for mCRPC patients. We also urge to strictly control the cocktail composition during any F-NaF/F-FDG cocktail PET/CT examination.

PET Imaging of Skeletal Metastases and Its Role in Personalizing Further Management

In oncology, the skeleton is one of the most frequently encountered sites for metastatic disease and thus early detection not only has an impact on an individual patient's management but also on the overall outcome. Multiparametric and multimodal hybrid PET/computed tomography and PET/MR imaging have revolutionized imaging for bone metastases, but irrespective of tumor biology or morphology of the bone lesion it remains unclear which imaging modality is the most clinically relevant to guide individualized cancer care. In this review, we highlight the current clinical challenges of PET imaging in evaluation and quantification of skeletal tumor burden and its impact on personalized cancer management.

Multi-technique imaging of bone metastases: spotlight on PET-CT

There is growing evidence that molecular imaging of bone metastases with positron-emission tomography (PET) can improve diagnosis and treatment response assessment over current conventional standard imaging methods, although cost-effectiveness has not been assessed. In most cancer types, 2-[(18)F]-fluoro-2-deoxy-d-glucose ((18)F-FDG)-PET is an accurate method for detecting bone metastases. For example, in breast cancer, combined (18)F-FDG-PET and computed tomography (CT) is more sensitive at detecting bone metastases than (99m)technetium (Tc)-labelled diphosphonate planar bone scintigraphy (BS) and there is increasing evidence to support the use of serial (18)F-FDG-PET for the assessment of osseous response to treatment. Preliminary data suggest improved diagnostic accuracy of (18)F-FDG-PET-CT in a number of other malignancies including lung, thyroid, head and neck, gastro-oesophageal cancers, and osteosarcoma. As a bone-specific tracer, there is accumulating evidence to support the use of sodium (18)F-fluoride ((18)F-NaF) PET-CT in the diagnosis of skeletal metastases in breast and prostate cancer, although relatively little data are available to support its use for assessment of treatment response. In prostate cancer, (11)C-choline and (18)F-choline PET-CT have better specificities than (18)F-NaF-PET-CT, but equivalent sensitivities in the detection of bone metastases. We review the current literature for staging and response assessment of bone metastases in different cancers.

Receiver operating characteristic (ROC) curve for classification of (18)F-NaF uptake on PET/CT

OBJECTIVE

To assess the cutoff values established by ROC curves to classify (18)F-NaF uptake as normal or malignant.

MATERIALS AND METHODS

PET/CT images were acquired 1 hour after administration of 185 MBq of (18)F-NaF. Volumes of interest (VOIs) were drawn on three regions of the skeleton as follows: proximal right humerus diaphysis (HD), proximal right femoral diaphysis (FD) and first vertebral body (VB1), in a total of 254 patients, totalling 762 VOIs. The uptake in the VOIs was classified as normal or malignant on the basis of the radiopharmaceutical distribution pattern and of the CT images. A total of 675 volumes were classified as normal and 52 were classified as malignant. Thirty-five VOIs classified as indeterminate or nonmalignant lesions were excluded from analysis. The standardized uptake value (SUV) measured on the VOIs were plotted on an ROC curve for each one of the three regions. The area under the ROC (AUC) as well as the best cutoff SUVs to classify the VOIs were calculated. The best cutoff values were established as the ones with higher result of the sum of sensitivity and specificity.

RESULTS

The AUCs were 0.933, 0.889 and 0.975 for UD, FD and VB1, respectively. The best SUV cutoffs were 9.0 (sensitivity: 73%; specificity: 99%), 8.4 (sensitivity: 79%; specificity: 94%) and 21.0 (sensitivity: 93%; specificity: 95%) for UD, FD and VB1, respectively.

CONCLUSION

The best cutoff value varies according to bone region of analysis and it is not possible to establish one value for the whole body.

Imaging Bone Metastases in Breast Cancer: Staging and Response Assessment

Bone metastases are common in patients with advanced breast cancer. Given the significant associated morbidity, the introduction of new, effective systemic therapies, and the improvement in survival time, early detection and response assessment of skeletal metastases have become even more important. Although planar bone scanning has recognized limitations, in particular, poor specificity in staging and response assessment, it continues to be the main method in current clinical practice for staging of the skeleton in patients at risk of bone metastases. However, the accuracy of bone scanning can be improved with the addition of SPECT/CT. There have been reported improvements in sensitivity and specificity for staging of the skeleton with either bone-specific PET/CT tracers, such as (18)F-NaF, or tumor-specific tracers, such as (18)F-FDG, although these methods are less widely available and more costly. There is a paucity of data on the use of (18)F-NaF PET/CT for response assessment in breast cancer, but there is increasing evidence that (18)F-FDG PET/CT may improve on current methods in this regard. At the same time, interest and experience in using whole-body morphologic MRI augmented with diffusion-weighted imaging for both staging and response assessment in the skeleton have been increasing. However, data on comparisons of these methods with PET methods to determine the best technique for current clinical practice or for clinical trials are insufficient. There are early data supporting the use (18)F-FDG PET/MRI to assess malignant disease in the skeleton, with the possibility of taking advantage of the synergies offered by combining morphologic, physiologic, and metabolic imaging.

Molecular and Functional Imaging of Bone Metastases in Breast and Prostate Cancers: An Overview

Our ability to accurately assess the skeleton for metastases in breast and prostate cancers has improved significantly in recent years with hybrid imaging methods. Nevertheless, no consensus has been reached on the best imaging modality for diagnosis and treatment response assessment of skeletal disease. Hybrid SPECT/CT has low false-positive and false-negative rates compared with planar bone scintigraphy (BS) or BS augmented with SPECT in breast and prostate cancers. In breast cancer, 18F-FDG PET is more sensitive and accurate at detecting bone metastases than BS. Currently, little evidence has accrued to support the superiority of 18F-fluoride (18F-NaF) PET in diagnosing osseous metastases or monitoring treatment response in breast cancer when compared with conventional imaging. In prostate cancer, the sensitivities of 18F-NaF PET/CT, 18F-fluorocholine (18F-choline), or 11C-choline PET/CT are equivalent, although 11C-/18F-choline PET/CT scans are more specific. Whole-body MRI, using anatomical sequences complemented by diffusion-weighted MRI, shows early evidence of utility for diagnosis and monitoring therapy response. We review the literature for staging and response assessment in metastatic breast and prostate cancer. While staging accuracy has significantly improved with hybrid imaging, optimal methods for assessing early treatment response have not been determined, and this is an area of active research.

Comparison of standardized uptake values measured on F-NaF PET/CT scans using three different tube current intensities

OBJECTIVE

To analyze standardized uptake values (SUVs) using three different tube current intensities for attenuation correction on (18)FNaF PET/CT scans.

MATERIALS AND METHODS

A total of 254 (18)F-NaF PET/CT studies were analyzed using 10, 20 and 30 mAs. The SUVs were calculated in volumes of interest (VOIs) drawn on three skeletal regions, namely, right proximal humeral diaphysis (RH), right proximal femoral diaphysis (RF), and first lumbar vertebra (LV1) in a total of 712 VOIs. The analyses covered 675 regions classified as normal (236 RH, 232 RF, and 207 LV1).

RESULTS

Mean SUV for each skeletal region was 3.8, 5.4 and 14.4 for RH, RF, and LV1, respectively. As the studies were grouped according to mAs value, the mean SUV values were 3.8, 3.9 and 3.7 for 10, 20 and 30 mAs, respectively, in the RH region; 5.4, 5.5 and 5.4 for 10, 20 and 30 mAs, respectively, in the RF region; 13.8, 14.9 and 14.5 for 10, 20 and 30 mAs, respectively, in the LV1 region.

CONCLUSION

The three tube current values yielded similar results for SUV calculation.

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.

Castration-resistant prostate cancer bone metastasis response measured by 18F-fluoride PET after treatment with dasatinib and correlation with progression-free survival: results from American College of Radiology Imaging Network 6687

(18)F-fluoride PET quantitatively images bone metabolism and may serve as a pharmacodynamic assessment for systemic therapy such as dasatinib, a potent SRC kinase inhibitor, with activity in bone.

METHODS

This was an imaging companion trial (American College of Radiology Imaging Network [ACRIN] 6687) to a multicenter metastatic castration-resistant prostate cancer (CRPC) tissue biomarker-guided therapeutic trial (NCT00918385). Men with bone metastatic CRPC underwent (18)F-fluoride PET before and 12 weeks after initiation of dasatinib (100 mg daily). Dynamic imaging was performed over a 15-cm field of view for trial assessments. The primary endpoint was to determine whether changes in (18)F-fluoride incorporation in tumor and normal bone occurred in response to dasatinib. Other endpoints included differential effect of dasatinib between (18)F-fluoride incorporation in tumor and normal bone, (18)F-fluoride transport in bone metastases, correlation with progression-free survival (PFS), prostate-specific antigen, and markers of bone turnover.

RESULTS

Eighteen participants enrolled, and 17 underwent interpretable baseline (18)F-fluoride PET imaging before initiation of dasatinib. Twelve of 17 patients underwent on-treatment PET imaging. Statistically significant changes in response to dasatinib were identified by the SUVmaxavg (average of maximum standardized uptake value [SUVmax] for up to 5 tumors within the dynamic field of view) in bone metastases (P = 0.0002), with a significant differential (18)F-fluoride PET response between tumor and normal bone (P < 0.0001). Changes in (18)F-fluoride incorporation in bone metastases had borderline correlation with PFS by SUVmaxavg (hazard ratio, 0.91; 95% confidence interval, 0.82-1.00; P = 0.056). Changes by SUVmaxavg correlated with bone alkaline phosphatase (P = 0.0014) but not prostate-specific antigen (P = 0.47).

CONCLUSION

This trial provides evidence of the ability (18)F-fluoride PET to delineate treatment response of dasatinib in CRPC bone metastases with borderline correlation with PFS.

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.

Comparison of NaF and FDG PET/CT for assessment of treatment response in castration-resistant prostate cancers with osseous metastases

BACKGROUND

Assessment of skeletal metastases' response to therapy is a highly relevant but unresolved clinical problem. The main goal of this work was to compare pharmacodynamic responses to therapy assessed with positron emission tomography-computed tomography (PET/CT) using fluorine-18 sodium fluoride (NaF) and fluorine-18 fluorodeoxyglucose (FDG) as the tracers.

MATERIALS AND METHODS

Patients with prostate cancer with known osseous metastases were treated with zibotentan (ZD4054) and imaged with combined dynamic NaF/FDG PET/CT before therapy (baseline), after 4 weeks of therapy (week 4), and after 2 weeks of treatment break (week 6). Kinetic analysis allowed comparison of the voxel-based tracer uptake rate parameter Ki, the vasculature parameters K1 (measuring perfusion/permeability) and Vb (measuring vasculature fraction in the tissue), and the standardized uptake values (SUVs).

RESULTS

Correlations were high for the NaF and FDG peak uptake parameters (Ki and SUV correlations ranged from 0.57 to 0.88) and for vasculature parameters (K1 and Vb correlations ranged from 0.61 to 0.81). Correlation was low between the NaF and FDG week 4 Ki responses (ρ = 0.35; P = .084) but was higher for NaF and FDG week 6 Ki responses (ρ = 0.72; P < .0001). Correlations for vasculature responses were always low (ρ < 0.35). NaF and FDG uptakes in the osseous metastases were spatially dislocated, with overlap in the range from 0% to 80%.

CONCLUSION

This study found that late NaF and FDG uptake responses are consistently correlated but that earlier uptake responses and all vasculature responses can be unrelated. This study also confirmed that FDG and NaF uptakes are spatially dislocated. Although treatment responses assessed with NaF and FDG may be correlated, using both tracers provides additional information.

The emerging science of quantitative imaging biomarkers terminology and definitions for scientific studies and regulatory submissions

The development and implementation of quantitative imaging biomarkers has been hampered by the inconsistent and often incorrect use of terminology related to these markers. Sponsored by the Radiological Society of North America, an interdisciplinary group of radiologists, statisticians, physicists, and other researchers worked to develop a comprehensive terminology to serve as a foundation for quantitative imaging biomarker claims. Where possible, this working group adapted existing definitions derived from national or international standards bodies rather than invent new definitions for these terms. This terminology also serves as a foundation for the design of studies that evaluate the technical performance of quantitative imaging biomarkers and for studies of algorithms that generate the quantitative imaging biomarkers from clinical scans. This paper provides examples of research studies and quantitative imaging biomarker claims that use terminology consistent with these definitions as well as examples of the rampant confusion in this emerging field. We provide recommendations for appropriate use of quantitative imaging biomarker terminological concepts. It is hoped that this document will assist researchers and regulatory reviewers who examine quantitative imaging biomarkers and will also inform regulatory guidance. More consistent and correct use of terminology could advance regulatory science, improve clinical research, and provide better care for patients who undergo imaging studies.

An Approach to Breast Cancer Diagnosis via PET Imaging of Microcalcifications Using (18)F-NaF

Current radiologic methods for diagnosing breast cancer detect specific morphologic features of solid tumors or any associated calcium deposits. These deposits originate from an early molecular microcalcification process of 2 types: type 1 is calcium oxylate and type II is carbonated calcium hydroxyapatite. Type I microcalcifications are associated mainly with benign tumors, whereas type II microcalcifications are produced internally by malignant cells. No current noninvasive in vivo techniques are available for detecting intratumoral microcalcifications. Such a technique would have a significant impact on breast cancer diagnosis and prognosis in preclinical and clinical settings. (18)F-NaF PET has been used solely for bone imaging by targeting the bone hydroxyapatite. In this work, we provide preliminary evidence that (18)F-NaF PET imaging can be used to detect breast cancer by targeting the hydroxyapatite lattice within the tumor microenvironment with high specificity and soft-tissue contrast-to-background ratio while delineating tumors from inflammation.

METHODS

Mice were injected with approximately 10(6) MDA-MB-231 cells subcutaneously and imaged with (18)F-NaF PET/CT in a 120-min dynamic sequence when the tumors reached a size of 200-400 mm(3). Regions of interest were drawn around the tumor, muscle, and bone. The concentrations of radiotracer within those regions of interest were compared with one another. For comparison to inflammation, rats with inflamed paws were subjected to (18)F-NaF PET imaging.

RESULTS

Tumor uptake of (18)F(-) was significantly higher (P < 0.05) than muscle uptake, with the tumor-to-muscle ratio being about 3.5. The presence of type II microcalcification in the MDA-MB-231 cell line was confirmed histologically using alizarin red S and von Kossa staining as well as Raman microspectroscopy. No uptake of (18)F(-) was observed in the inflamed tissue of the rats. Lack of hydroxyapatite in the inflamed tissue was verified histologically.

CONCLUSION

This study provides preliminary evidence suggesting that specific targeting with (18)F(-) of hydroxyapatite within the tumor microenvironment may be able to distinguish between inflammation and cancer.

Use of articulated registration for response assessment of individual metastatic bone lesions

Accurate skeleton registration is necessary to match corresponding metastatic bone lesions for response assessment over multiple scans. In articulated registration (ART), whole-body skeletons are registered by auto-segmenting individual bones, then rigidly aligning them. Performance and robustness of the ART in lesion matching were evaluated and compared to other commonly used registration techniques. Sixteen prostate cancer patients were treated either with molecular targeted therapy or chemotherapy. Ten out of the 16 patients underwent the double baseline whole-body [F-18]NaF PET/CT scans for test-retest (TRT) evaluation. Twelve of the 16 patients underwent pre- and mid-treatment [F-18]NaF PET/CT scans. Skeletons at different time points were registered using ART, rigid, and deformable (DR) registration algorithms. The corresponding lesions were contoured and identified on successive PET images based on including the voxels with the standardized uptake value over 15. Each algorithm was evaluated for its ability to accurately align corresponding lesions via skeleton registration. A lesion matching score (MS) was measured for each lesion, which quantified the per cent overlap between the lesion's two corresponding contours. Three separate sensitivity studies were conducted to investigate the robustness of ART in matching: sensitivity of lesion matching to various contouring threshold levels, effects of imperfections in the bone auto-segmentation and sensitivity of mis-registration. The performance of ART (MS = 82% for both datasets, p ≪ 0.001) in lesion matching was significantly better than rigid (MS(TRT)=53%, MS(Response)= 46%) and DR (MS(TRT)=46%, MS(Response)=45%) algorithms. Neither varying threshold levels for lesion contouring nor imperfect bone segmentation had significant (p~0.10) impact on the ART matching performance as the MS remained unchanged. Despite the mis-registration reduced MS for ART, as low as 67% (p ≪ 0.001), the performance remained to be superior to the rigid and DR algorithms. ART is not only robust to contouring threshold levels for bone lesions, but also outperforms rigid and DR algorithms in lesion matching. ART therefore enables the study of TRT variability and treatment assessment of individual bone lesions.

Nitric oxide-mediated vasodilation increases blood flow during the early stages of stress fracture healing

Despite the strong connection between angiogenesis and osteogenesis in skeletal repair conditions such as fracture and distraction osteogenesis, little is known about the vascular requirements for bone formation after repetitive mechanical loading. Here, established protocols of damaging (stress fracture) and nondamaging (physiological) forelimb loading in the adult rat were used to stimulate either woven or lamellar bone formation, respectively. Positron emission tomography was used to evaluate blood flow and fluoride kinetics at the site of bone formation. In the group that received damaging mechanical loading leading to woven bone formation (WBF), (15)O water (blood) flow rate was significantly increased on day 0 and remained elevated 14 days after loading, whereas (18)F fluoride uptake peaked 7 days after loading. In the group that received nondamaging mechanical loading leading to lamellar bone formation (LBF), (15)O water and (18)F fluoride flow rates in loaded limbs were not significantly different from nonloaded limbs at any time point. The early increase in blood flow rate after WBF loading was associated with local vasodilation. In addition, Nos2 expression in mast cells was increased in WBF-, but not LBF-, loaded limbs. The nitric oxide (NO) synthase inhibitor N(ω)-nitro-l-arginine methyl ester was used to suppress NO generation, resulting in significant decreases in early blood flow rate and bone formation after WBF loading. These results demonstrate that NO-mediated vasodilation is a key feature of the normal response to stress fracture and precedes woven bone formation. Therefore, patients with impaired vascular function may heal stress fractures more slowly than expected.

Monitoring the clinical outcomes in advanced prostate cancer: what imaging modalities and other markers are reliable?

Effective patient care and efficient drug development require accurate tools to assess treatment effects. For metastatic castration-resistant prostate cancer (mCRPC), response biomarkers have historically been poorly reproducible, inaccurate, inconsistently applied, or only loosely associated with tangible clinical benefits such as survival. However, the field of response assessments for prostate cancer is maturing, in compliance with a rigorous process defined by analytic validation, clinical validation, and clinical qualification. For example, bone imaging with technetium-99m scintigraphy has historically been poorly used in prostate cancer clinical trials and routine patient care, and frequently has led to poor decision-making. However, contemporary clinical trial consensus criteria (Prostate Cancer Working Group 2 [PCWG2]) have standardized the definition of progression on bone scintigraphy and the clinical trials endpoint of radiographic progression-free survival (rPFS). A validated bone scan interpretation form captures the relevant data elements. rPFS and the forms have been undergoing prospective testing in multiple phase III studies. The first of these trials demonstrated a high degree of reproducibility and correlation with overall survival, and rPFS was used by the US Food and Drug Administration (FDA) for approval of abiraterone in chemotherapy-naïve mCRPC. Circulating tumor cells (CTC) are another class of assays with significant promise as response-indicator biomarkers. CTC enumeration has undergone analytic validation and has been FDA-cleared for monitoring patients with prostate cancer in conjunction with other clinical methods. It is not yet a surrogate for survival. Patient-reported outcomes (PROs) are direct indicators of patient benefit. The assays to measure PROs must undergo each of the steps of biomarker development, and are increasingly being standardized and used as clinical trial endpoints. In this review, we critically assess each of these classes of novel biomarkers--imaging, CTC, and PROs--in regard to the quality of data supporting their use to monitor clinical outcomes in advanced prostate cancer.

Quantification of skeletal blood flow and fluoride metabolism in rats using PET in a pre-clinical stress fracture model

PURPOSE

Blood flow is an important factor in bone production and repair, but its role in osteogenesis induced by mechanical loading is unknown. Here, we present techniques for evaluating blood flow and fluoride metabolism in a pre-clinical stress fracture model of osteogenesis in rats.

PROCEDURES

Bone formation was induced by forelimb compression in adult rats. (15)O water and (18)F fluoride PET imaging were used to evaluate blood flow and fluoride kinetics 7 days after loading. (15)O water was modeled using a one-compartment, two-parameter model, while a two-compartment, three-parameter model was used to model (18)F fluoride. Input functions were created from the heart, and a stochastic search algorithm was implemented to provide initial parameter values in conjunction with a Levenberg-Marquardt optimization algorithm.

RESULTS

Loaded limbs are shown to have a 26% increase in blood flow rate, 113% increase in fluoride flow rate, 133% increase in fluoride flux, and 13% increase in fluoride incorporation into bone as compared to non-loaded limbs (p < 0.05 for all results).

CONCLUSIONS

The results shown here are consistent with previous studies, confirming this technique is suitable for evaluating the vascular response and mineral kinetics of osteogenic mechanical loading.

(18)F-Deoxyglucose (FDG) kinetics evaluated by a non-compartment model based on a linear regression function using a computer based simulation: correlation with the parameters of the two-tissue compartment model

Parametric imaging with a linear regression function of the tracer activity curve fit is a non-compartmental method, which can be used for the evaluation of dynamic PET (dPET) studies. However, the dependency of the slope of the regression function fit on the (18)F-Deoxyglucose (FDG) 2-tissue compartment parameters (vb, k1-k4) is not known yet. This study is focused on the impact of the 2-tissue compartment parameters on the slope of the curve. A data base of 1760 dynamic PET FDG studies with the corresponding 2-tissue compartment model parameter solutions were available and used to calculate synthetic time-activity data based on the 2-tissue compartment model. The input curve was calculated from the median values of the input curves of the 1760 dynamic data sets. Then, sequentially each of the five parameters (vb, k1-k4) of the 2-tissue compartment model was varied from 0.1 to 0.9 and tracer activity curves were calculated (60000 curves/parameter). A linear regression function was fitted to these curves. The comparison of the slope values of the regression function with the corresponding compartment data revealed a primary dependency on k3, which is associated with the intracellular phosphorylation of FDG. The squared correlation coefficient was high with r(2)=0.9716, which refers to 97 % explained variance of the data. k2 and vb had only a minor impact, while k1 and k4 had no impact on the slope values. The results demonstrate, that k3 has a major impact on the slope values calculated by the linear regression function.

Diagnostic imaging and image-guided therapy of skeletal metastases

BACKGROUND

The high incidence of skeletal metastases in cancer patients warrants careful detection with imaging and follow-up. Efforts are needed to manage pain associated with skeletal metastases as part of overall patient management.

METHODS

This article reviews the current methods of diagnostic imaging in the evaluation of skeletal metastases and image-guided treatment of bone metastases for the palliation of pain based primarily on the assessment of imaging and interventional radiologic literature.

RESULTS

Approaches to diagnostic imaging of skeletal metastases are summarized. Skeletal scintigraphy provides high sensitivity for detecting skeletal metastases, but targeted computed tomography (CT) or magnetic resonance imaging (MRI) may be needed to increase specificity. Newer imaging modalities, such as positron emission tomography (PET)/CT, improve detection of both lytic and blastic metastases. Minimally invasive percutaneous ablative treatment techniques, including radiofrequency ablation, microwave ablation, and cryoablation, are examined. They provide alternative approaches to radiation therapy to effectively palliate pain of bone metastases. Preliminary results of MR-guided focused ultrasound surgery (MRgFUS) demonstrate its effectiveness in palliating pain from skeletal metastases.

CONCLUSIONS

Skeletal scintigraphy is the most common imaging modality for detecting skeletal metastases. Additional imaging may be required based on the type of tumor, the disease state, or treatment options. External-beam radiation therapy remains the mainstay for palliation of pain from bone metastases. Alternative minimally invasive and noninvasive image-guided treatment options can provide effective pain palliation.

Importance of quantification for the analysis of PET data in oncology: review of current methods and trends for the future

In oncology, positron emission tomography (PET) is an important tool for tumour diagnosis and staging, assessment of response to treatment and evaluation of the pharmacokinetic properties and efficacy of new drugs. Despite its quantitative potential, however, in daily clinical practice PET is used almost exclusively with 2-deoxy-2-[(18)F]fluoro-D-glucose ([(18)F]FDG) and, in addition, [(18)F]FDG data are normally assessed visually or using simple indices as the standardised uptake value (SUV). After explaining why more sophisticated quantification methods can be useful in oncology, the paper reviews the approaches that are commonly used and those available but not routinely employed. Particular emphasis is addressed to the SUV, for its importance in clinical practice. Issues specific to PET quantification in oncology and related examples are then discussed. Finally, some ideas for the development of new quantitative methods for analysing PET data in oncology and for the application of approaches already existing but not commonly employed are presented.

Dynamic PET-CT studies for characterizing nasopharyngeal carcinoma metabolism: comparison of analytical methods

OBJECTIVES

To investigate the optimal PET protocol and analytical method to characterize the glucose metabolism in nasopharyngeal carcinoma (NPC).

METHODS

Newly diagnosed NPC patients were recruited and a dynamic PET-CT scan was performed. The optimized threshold to derive the arterial input function (AIF) was studied. Two-tissue compartmental kinetic modeling using three, four, and five parameters, Patlak graphical analysis, and time sensitivity (S-factor) analysis were performed. The best compartmental model was determined in terms of goodness of fit, and correlated with Ki from Patlak graphical analysis and the S-factor. The methods with R>0.9 and P<0.05 were considered acceptable. The protocols using two static scans with its retention index (RI=(SUV(2)/SUV(1)-1)×100%, where SUV is the standardized uptake value) were also studied and compared with S-factor analysis.

RESULTS

The best threshold of 0.6 was determined and used to derive AIF. The kinetic model with five parameters yields the best statistical results, but the model with k4=0 was used as the gold standard. All Ki values and some S-factors from data between various intervals (10-30, 10-45, 15-30, 15-45, 20-30, and 20-45 min) fulfilled the criteria. The RIs calculated from the S-factor were highly correlated to RI derived from simple two-point static scans at 10 and 30 min (R=0.9, P<0.0001).

CONCLUSION

The Patlak graphical analyses and even a 20-min-interval S-factor analysis or simple two-point static scans were shown to be sufficient to characterize NPC metabolism, confirming the clinical feasibility of applying a short dynamic with image-derived AIF or simple two-point static PET scans for studying NPC.

Advances in molecular imaging for breast cancer detection and characterization

Advances in our ability to assay molecular processes, including gene expression, protein expression, and molecular and cellular biochemistry, have fueled advances in our understanding of breast cancer biology and have led to the identification of new treatments for patients with breast cancer. The ability to measure biologic processes without perturbing them in vivo allows the opportunity to better characterize tumor biology and to assess how biologic and cytotoxic therapies alter critical pathways of tumor response and resistance. By accurately characterizing tumor properties and biologic processes, molecular imaging plays an increasing role in breast cancer science, clinical care in diagnosis and staging, assessment of therapeutic targets, and evaluation of responses to therapies. This review describes the current role and potential of molecular imaging modalities for detection and characterization of breast cancer and focuses primarily on radionuclide-based methods.

Can PET-CT imaging and radiokinetic analyses provide useful clinical information on atypical femoral shaft fracture in osteoporotic patients?

Atypical femoral shaft fractures are associated with the extended usage of nitrogen-containing bisphosphonates as therapy for osteoporosis. For such fractures, the positron emission tomography (PET) procedure, coupled with computerized tomography (CT), provides a potential imaging modality for defining aspects of the pathogenesis, site specificity, and possible prodromal abnormalities prior to fracture. PET-CT may assess the radiokinetic variables K1 (a putative marker for skeletal blood flow) and Ki (a putative marker for skeletal bone formation), and when combined with PET imaging modalities and CT skeletal site localization, may define the site of such radiokinetic findings. Further studies into the clinical usage of PET-CT in patients with atypical femoral shaft fractures are warranted.

Clinical utility of (18)F-fluoride PET/CT in benign and malignant bone diseases

(18)F labeled sodium fluoride is a positron-emitting, bone seeking agent with more favorable skeletal kinetics than conventional phosphate and diphosphonate compounds. With the expanding clinical usage of PET/CT, there is renewed interest in using (18)F-fluoride PET/CT for imaging bone diseases. Growing evidence indicates that (18)F fluoride PET/CT offers increased sensitivity, specificity, and diagnostic accuracy in evaluating metastatic bone disease compared to (99m)Tc based bone scintigraphy. National Oncologic PET Registry (NOPR) has expanded coverage for (18)F sodium fluoride PET scans since February 2011 for the evaluation of osseous metastatic disease. In this article, we reviewed the pharmacological characteristics of sodium fluoride, as well as the clinical utility of PET/CT using (18)F-fluoride in both benign and malignant bone disorders.

Combining dynamic and ECG-gated ⁸²Rb-PET for practical implementation in the clinic

OBJECTIVES

For many cardiac clinics, list-mode PET is impractical. Therefore, separate dynamic and ECG-gated acquisitions are needed to detect harmful stenoses, indicate affected coronary arteries, and estimate stenosis severity. However, physicians usually order gated studies only because of dose, time, and cost limitations. These gated studies are limited to detection. In an effort to remove these limitations, we developed a novel curve-fitting algorithm [incomplete data (ICD)] to accurately calculate coronary flow reserve (CFR) from a combined dynamic-ECG protocol of a length equal to a typical gated scan.

METHODS

We selected several retrospective dynamic studies to simulate shortened dynamic acquisitions of the combined protocol and compared (a) the accuracy of ICD and a nominal method in extrapolating the complete functional form of arterial input functions (AIFs); and (b) the accuracy of ICD and ICD-AP (ICD with a-posteriori knowledge of complete-data AIFs) in predicting CFRs.

RESULTS

According to the Akaike information criterion, AIFs predicted by ICD were more accurate than those predicted by the nominal method in 11 out of 12 studies. CFRs predicted by ICD and ICD-AP were similar to complete-data predictions (PICD=0.94 and PICD-AP=0.91) and had similar average errors (eICD=2.82% and eICD-AP=2.79%).

CONCLUSION

According to a nuclear cardiologist and an expert analyst of PET data, both ICD and ICD-AP predicted CFR values with sufficient accuracy for the clinic. Therefore, by using our method, physicians in cardiac clinics would have access to the necessary amount of information to differentiate between single-vessel and triple-vessel disease for treatment decision making.