Update on imaging in chronic kidney disease-mineral and bone disorder: promising role of functional imaging

Disorders of mineral metabolism and bone disease are common complications in chronic kidney disease (CKD) patients and are associated with increased morbidity and mortality. Bone biopsies, bone scintigraphy, biochemical markers, and plain films have been used to assess bone disorders and bone turnover. Of these, functional imaging is less invasive than bone/marrow sampling, more specific than serum markers and is therefore ideally placed to assess total skeletal metabolism. ¹⁸F-sodium fluoride (NaF) PET/CT is an excellent bone-seeking agent superior to conventional bone scan in CKD patients due to its high bone uptake, rapid single-pass extraction, and minimal binding to serum proteins. Due to these properties, ¹⁸F-NaF can better assess the skeletal metabolism on primary diagnosis and following treatment in CKD patients. With the increased accessibility of PET scanners, it is likely that PET scanning with bone-specific tracers such as ¹⁸F-NaF will be used more regularly for clinical assessment and quantitation of bone kinetics. This article describes the pattern of scintigraphic/functional appearances secondary to musculoskeletal alterations that might occur in patients with CKD.

18F-Sodium Fluoride (NaF) Uptake in Calcified Bladder Carcinoma: Double Density Sign

¹⁸F-Sodium fluoride (NaF) is primarily a skeletal imaging agent which can be localized in extraosseous calcified foci. Here, we describe a case of a 48-year-old man with bladder carcinoma referred for staging using ¹⁸F-NaF positron emission tomography/computed tomography (PET/CT). ¹⁸F-NaF PET/CT detected a calcified soft tissue mass in the urinary bladder. Extraosseous ¹⁸F-NaF uptake is often encountered and these non-osseous findings could possibly provide important diagnostic information. Thus, recognition of extraosseous ¹⁸F-NaF activity has implications for accurate staging and management.

Skin and Arterial Wall Deposits of 18F-NaF and Severity of Disease in Patients with Pseudoxanthoma Elasticum

Pseudoxanthoma elasticum (PXE) is a genetic disease characterized by the calcification of elastin fibers. Our aim was to quantify vascular calcification in the arteries and the deposition of 18F-sodium-fluoride (18F-NaF) in the skin and vessel walls with positron emission tomography/computed tomography. This was an observational study including 18 patients with PXE. Vascular calcification was measured in Agatston units, and deposition in the skin and vessel walls was shown using target-to-background ratio (TBR). Severity of the disease was scored by Phenodex. We found higher vascular calcification in the popliteal, femoral, and aortic arch vessels compared to other vascular regions; however, the uptake of radiotracer was the highest in the aorta and femoral arteries. In the skin, the highest uptake was observed in the neck and the axillae. There was no significant association between 18F-NaF deposition in the arteries or skin and the global Phenodex score. In contrast, the Phenodex score was significantly associated in univariate analyses with the averaged vascular calcium score (p < 0.01). In the neck, patients with higher skin Phenodex scores exhibited higher radiotracer uptake. As a conclusion, because vascular calcification is physiological, our data suggested that the detection of cutaneous (neck) 18F-NaF deposits might serve to monitor the calcification process in the short-term for patients with PXE.

Textitis as Seen on 18F-NaF Imaging Using an Ultra-High-Resolution Positron Emission Mammography Scanner

Textitis is a new term used to refer to the degenerative-strain osteoarthritis that comes from excessive use of a smart phone. ¹⁸F-NaF is increasingly used in diagnosing skeletal pain that is not identified on radiographs. We report a case of a 26-y-old woman with left breast cancer referred for ¹⁸F-NaF PET/CT, who was complaining of right thumb and wrist pain. Findings were negative for bone secondaries. Dedicated hands views were acquired on a positron emission mammography scanner and showed focal uptake at the first carpometacarpal and second metacarpophalangeal joints. On the basis of the strong history, the findings were likely due to active arthritic changes caused by repetitive strain injury from excessive text messaging.

18F-NaF PET/CT imaging of bone formation induced by bioactive glass S53P4 after mastoid obliteration

Purpose

Bioactive glass has been successfully used for surgical treatment of chronic infections in bone and bone cavities. Besides infection control, new bone formation is induced by the bioactive glass which is considered to have osteoconductive properties. Evaluation of postsurgical changes after bone graft surgery is generally performed with conventional radiographs or CT/MR imaging, but 18F-NaF PET/CT might be more suitable since it has a high and rapid bone uptake, accompanied by a fast blood clearance leading to a high bone to background ratio.

Case

Obliteration with S53P4 bioactive glass of the mastoid and middle ear was performed in a patient suffering from chronic otitis media. Control of the chronic otitis media was achieved, and follow-up imaging after 3 years with 18F-NaF PET/CT showed increased uptake in the obliterated cavity indicating new bone formation.

Conclusion

18F-NaF PET/CT is able to detect new bone formation after obliteration of the mastoid with S53P4 bioactive glass.

Comparison of [68Ga]Ga-PSMA-11 PET/CT with [18F]NaF PET/CT in the evaluation of bone metastases in metastatic prostate cancer patients prior to radionuclide therapy

AIM

The purpose of this study was to investigate the diagnostic performance of ⁶⁸Ga-PSMA-11 PET/CT in the evaluation of bone metastases in metastatic prostate cancer (PC) patients scheduled for radionuclide therapy in comparison to [¹⁸F]sodium fluoride (¹⁸F-NaF) PET/CT.

METHODS

Sixteen metastatic PC patients with known skeletal metastases, who underwent both ⁶⁸Ga-PSMA-11 PET/CT and ¹⁸F-NaF PET/CT for assessment of metastatic burden prior to radionuclide therapy, were analysed retrospectively. The performance of both tracers was calculated on a lesion-based comparison. Intensity of tracer accumulation of pathologic bone lesions on ¹⁸F-NaF PET and ⁶⁸Ga-PSMA-11 PET was measured with maximum standardized uptake values (SUV_max) and compared to background activity of normal bone. In addition, SUV_max values of PET-positive bone lesions were analysed with respect to morphologic characteristics on CT. Bone metastases were either confirmed by CT or follow-up PET scan.

RESULTS

In contrast to 468 PET-positive lesions suggestive of bone metastases on ¹⁸F-NaF PET, only 351 of the lesions were also judged positive on ⁶⁸Ga-PSMA-11 PET (75.0%). Intensity of tracer accumulation of pathologic skeletal lesions was significantly higher on ¹⁸F-NaF PET compared to ⁶⁸Ga-PSMA-11 PET, showing a median SUV_max of 27.0 and 6.0, respectively (p < 0.001). Background activity of normal bone was lower on ⁶⁸Ga-PSMA-11 PET, with a median SUV_max of 1.0 in comparison to 2.7 on ¹⁸F-NaF PET; however, tumour to background ratio was significantly higher on ¹⁸F-NaF PET (9.8 versus 5.9 on ⁶⁸Ga-PSMA-11 PET; p = 0.042). Based on morphologic lesion characterisation on CT, ¹⁸F-NaF PET revealed median SUV_max values of 23.6 for osteosclerotic, 35.0 for osteolytic, and 19.0 for lesions not visible on CT, whereas on ⁶⁸Ga-PSMA-11 PET median SUV_max values of 5.0 in osteosclerotic, 29.5 in osteolytic, and 7.5 in lesions not seen on CT were measured. Intensity of tracer accumulation between¹⁸F-NaF PET and ⁶⁸Ga-PSMA-11 PET was significantly higher in osteosclerotic (p < 0.001) and lesions not visible on CT (p = 0.012).

CONCLUSION

In comparison to ⁶⁸Ga-PSMA-11 PET/CT, ¹⁸F-NaF PET/CT detects a higher number of pathologic bone lesions in advanced stage PC patients scheduled for radionuclide therapy. Our data suggest that ⁶⁸Ga-PSMA-11 PET should be combined with ¹⁸F-NaF PET in PC patients with skeletal metastases for restaging prior to initiation or modification of therapy.

Pictorial atlas of symptomatic accessory ossicles by 18F-Sodium Fluoride (NaF) PET-CT

Accessory ossicles are developmental variants which are often asymptomatic. When incidentally picked up on imaging, they are often inconsequential and rarely a cause for concern. However, they may cause pain or discomfort due to trauma, altered stress, and over-activity. Nuclear scintigraphy may play a role in the diagnosis and localizing pain generators. ¹⁸F-Sodium Fluoride (NaF) is a PET imaging agent used in bone imaging. Although commonly used in imaging patients with cancer imaging malignancy, ¹⁸F-NaF may be useful in the evaluation of benign bone and joint conditions. In this article, we would like to present a spectrum of clinical cases and review the potential diagnostic utility of ¹⁸F-NaF in the assessment of symptomatic accessory ossicles in patients referred for staging cancers.

Radium-223 IN metastatic hormone-sensitive high-grade prostate cancer: initial experience

Our study evaluates the feasibility of compassionate exemption of Radium-223 (²²³Ra) treatment in metastatic hormone-sensitive high-grade prostate cancer (mHSHGPC) patients with concomitant androgen deprivation-therapy (ADT). Seven patients with mHSHGPC, were treated with six cycles of ²²³Ra plus ADT. All patients had undergone to ¹⁸F-NaF-PET/CT. A qualitative analyses of the ¹⁸F-NaF-PET/CT was performed in conjunction with Alkaline Phosphatase (ALP), Lactate-dehydrogenase (LDH) and Prostatic-Specific Antigen (PSA) values. The mean of SUVmax values were used as a quantitative measure of tumoral burden. Changes in PSA, ALP, LDH from baseline were evaluated, and were defined as increase or decrease of at least 30%. Clinical response was achieved if there was pain reduction using visual analogic scale. Four patients showed a significant reduction in mean SUVmax after 3 cycles of ²²³Ra, and one after 6 cycles. Patients who showed reductions in mean SUVmax after Ra-223 also showed reductions in PSA, ALP and LDH. Four weeks after the last cycle of ²²³Ra all patients had decreased total PSA, ALP and LDH values ≥ 30% also significant improvement on pain. No progress disease was documented after 14 ± 4 weeks. We found slight to moderate decreases in neutrophils and hemoglobin in two patients. We concluded that ²²³Ra plus ADT can be useful in mHSHGPC; the semi-quantitative ¹⁸F-NaF-PET/CT as a method effective to monitor the treatment response. Due to concomitant administration of ADT, ¹⁸F-NaF-PET/CT cannot differentiate whether the findings were due to androgen blockade or the ²²³Ra; nevertheless, data supporting the efficacy of ²²³Ra is the significant improvement on pain.

Vertebral and femoral bone mineral density and bone strength in prostate cancer patients assessed in phantomless PET/CT examinations

PURPOSE

Bone fracture risk assessed ancillary to positron emission tomography with computed tomography co-registration (PET/CT) could provide substantial clinical value to oncology patients with elevated fracture risk without introducing additional radiation dose. The purpose of our study was to investigate the feasibility of obtaining valid measurements of bone mineral density (BMD) and finite element analysis-derived bone strength of the hip and spine using PET/CT examinations of prostate cancer patients by comparing against values obtained using routine multidetector-row computed tomography (MDCT) scans-as validated in previous studies-as a reference standard.

MATERIALS AND METHODS

Men with prostate cancer (n=82, 71.6±8.3 years) underwent Fluorine-18 NaF PET/CT and routine MDCT within three months. Femoral neck and total hip areal BMD, vertebral trabecular BMD and femur and vertebral strength based on finite element analysis were assessed in 63 paired PET/CT and MDCT examinations using phantomless calibration and Biomechanical-CT analysis. Men with osteoporosis or fragile bone strength identified at either the hip or spine (vertebral trabecular BMD ≤80mg/cm³, femoral neck or total hip T-score ≤-2.5, vertebral strength ≤6500N and femoral strength ≤3500N, respectively) were considered to be at high risk of fracture. PET/CT- versus MDCT-based BMD and strength measurements were compared using paired t-tests, linear regression and by generating Bland-Altman plots. Agreement in fracture-risk classification was assessed in a contingency table.

RESULTS

All measurements from PET/CT versus MDCT were strongly correlated (R²=0.93-0.97; P<0.0001 for all). Mean differences for total hip areal BMD (0.001g/cm², 1.1%), femoral strength (-60N, 1.3%), vertebral trabecular BMD (2mg/cm³, 2.6%) and vertebral strength (150N; 1.7%) measurements were not statistically significant (P>0.05 for all), whereas the mean difference in femoral neck areal BMD measurements was small but significant (-0.018g/cm²; -2.5%; P=0.007). The agreement between PET/CT and MDCT for fracture-risk classification was 97% (0.89 kappa for repeatability).

CONCLUSION

Ancillary analyses of BMD, bone strength, and fracture risk agreed well between PET/CT and MDCT, suggesting that PET/CT can be used opportunistically to comprehensively assess bone integrity. In subjects with high fracture risk such as cancer patients this may serve as an additional clinical tool to guide therapy planning and prevention of fractures.

Evaluation of Prostate Cancer Bone Metastases with 18F-NaF and 18F-Fluorocholine PET/CT

¹⁸F-fluorocholine is a specific promising agent for imaging tumor cell proliferation, particularly in prostate cancer, using PET/CT. It is a beneficial tool in the early detection of marrow-based metastases because it excludes distant metastases and evaluates the response to hormone therapy. In addition, ¹⁸F-fluorocholine has the potential to differentiate between degenerative and malignant osseous abnormalities because degenerative changes are not choline-avid; however, the agent may accumulate in recent traumatic bony lesions. On the other hand, ¹⁸F-NaF PET/CT can indicate increased bone turnover and is generally used in the assessment of primary and secondary osseous malignancies, the evaluation of response to treatment, and the clarification of abnormalities on other imaging modalities or clinical data. ¹⁸F-NaF PET/CT is a highly sensitive method in the evaluation of bone metastases from prostate cancer, but it has problematic specificity, mainly because of tracer accumulation in degenerative and inflammatory bone diseases. In summary, ¹⁸F-NaF PET/CT is a highly sensitive method, but ¹⁸F-fluorocholine PET/CT can detect early bone marrow metastases and provide greater specificity in the detection of bone metastases in patients with prostate cancer. However, the difference seems not to be significant.

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.

Prospective study evaluating the relative sensitivity of 18F-NaF PET/CT for detecting skeletal metastases from renal cell carcinoma in comparison to multidetector CT and 99mTc-MDP bone scintigraphy, using an adaptive trial design

BACKGROUND

The detection of occult bone metastases is a key factor in determining the management of patients with renal cell carcinoma (RCC), especially when curative surgery is considered. This prospective study assessed the sensitivity of (18)F-labelled sodium fluoride in conjunction with positron emission tomography/computed tomography ((18)F-NaF PET/CT) for detecting RCC bone metastases, compared with conventional imaging by bone scintigraphy or CT.

PATIENTS AND METHODS

An adaptive two-stage trial design was utilized, which was stopped after the first stage due to statistical efficacy. Ten patients with stage IV RCC and bone metastases were imaged with (18)F-NaF PET/CT and (99m)Tc-labelled methylene diphosphonate ((99m)Tc-MDP) bone scintigraphy including pelvic single photon emission computed tomography (SPECT). Images were reported independently by experienced radiologists and nuclear medicine physicians using a 5-point scoring system.

RESULTS

Seventy-seven lesions were diagnosed as malignant: 100% were identified by (18)F-NaF PET/CT, 46% by CT and 29% by bone scintigraphy/SPECT. Standard-of-care imaging with CT and bone scintigraphy identified 65% of the metastases reported by (18)F-NaF PET/CT. On an individual patient basis, (18)F-NaF PET/CT detected more RCC metastases than (99m)Tc-MDP bone scintigraphy/SPECT or CT alone (P = 0.007). The metabolic volumes, mean and maximum standardized uptake values (SUV mean and SUV max) of the malignant lesions were significantly greater than those of the benign lesions (P < 0.001).

CONCLUSIONS

(18)F-NaF PET/CT is significantly more sensitive at detecting RCC skeletal metastases than conventional bone scintigraphy or CT. The detection of occult bone metastases could greatly alter patient management, particularly in the context when standard-of-care imaging is negative for skeletal metastases.

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.

Impact of Nonosseous Findings on (18)F-NaF PET/CT in a Patient with Ductal Breast Carcinoma

(18)F-NaF was used as a bone-seeking PET tracer for skeletal imaging until the introduction of the widely available (99m)Tc-labeled bone agents. However, there is renewed clinical interest in (18)F-NaF since prior technical and logistic limitations to its routine use are no longer present, and, as a consequence, it is likely that uptake unrelated to bone and non-osseous findings will be encountered more frequently. As a result of tumoral necrosis, soft tissue metastases may demonstrate (18)F-NaF avidity due to dystrophic calcification. On the other hand, all non-osseous findings, whether (18)F-NaF avid or not, may provide important diagnostic information that may alter the course of the disease, including treatment options. Herein we present a patient with ductal carcinoma of the breast in whom findings unrelated to the skeletal system in (18)F-NaF PET/CT altered the treatment strategy.