Anti-1-amino-3-18F-fluorocyclobutane-1-carboxylic acid: physiologic uptake patterns, incidental findings, and variants that may simulate disease

Anti-1-amino-3-(18)F-fluorocyclobutane-1-carboxylic acid ((18)F-FACBC) is a synthetic amino acid analog PET radiotracer undergoing clinical trials for the evaluation of prostate and other cancers. We aimed to describe common physiologic uptake patterns, incidental findings, and variants in patients who had undergone (18)F-FACBC PET.

METHODS

Sixteen clinical trials involving 611 (18)F-FACBC studies from 6 centers, which included dosimetry studies on 12 healthy volunteers, were reviewed. Qualitative observations of common physiologic patterns, incidental uptake, and variants that could simulate disease were recorded and compared with similar observations in studies of the healthy volunteers. Quantitative analysis of select data and review of prior published reports and observations were also made.

RESULTS

The liver and pancreas demonstrated the most intense uptake. Moderate salivary and pituitary uptake and variable mild to moderate bowel activity were commonly visualized. Moderate bone marrow and mild muscle activity were present on early images, with marrow activity decreasing and muscle activity increasing with time. Brain and lungs demonstrated activity less than blood pool. Though (18)F-FACBC exhibited little renal excretion or bladder uptake during the clinically useful early imaging time window, mild to moderate activity might accumulate in the bladder and interfere with evaluation of adjacent prostate bed and seminal vesicles in 5%-10% of patients. Uptake might also occur from benign processes such as infection, inflammation, prostatic hyperplasia, and metabolically active benign bone lesions such as osteoid osteoma.

CONCLUSION

Common physiologic uptake patterns were similar to those noted in healthy volunteers. The activity in organs followed the presence of amino acid transport and metabolism described with other amino acid-based PET radiotracers. As with other PET radiotracers such as (18)F-FDG, focal nonphysiologic uptake may represent incidental malignancy. Uptake due to benign etiologies distinct from physiologic background also occurred and could lead to misinterpretations if the reader is unaware of them.

Clinical Significance of Diffusely Increased 18F-FDG Uptake in the Thyroid Gland

Our purpose was to determine the clinical significance of diffusely increased (18)F-FDG uptake in the thyroid gland as an incidental finding on PET/CT.

METHODS

All patients who were found to have diffuse thyroid uptake on (18)F-FDG PET/CT in our institution between November 2004 and June 2006 were investigated and compared with an age- and sex-matched control group. The (18)F-FDG uptake in the thyroid was semiquantified using maximum standardized uptake value and correlated to the available serum thyroid-stimulating hormone (TSH) and thyroid peroxidase (TPO) antibody levels using regression analysis.

RESULTS

Of the 4,732 patients, 138 (2.9%) had diffuse thyroid uptake. Clinical information was available for 133 of the 138 patients. Sixty-three (47.4%) had a prior diagnosis of hypothyroidism or autoimmune thyroiditis, of whom 56 were receiving thyroxine therapy. In the control group, consisting of 133 patients with no thyroid uptake, there were 13 (9.8%) with a prior diagnosis of hypothyroidism, 11 of whom were receiving thyroxine therapy. In the study group, 38 (28.6%) of 133 patients did not undergo any further investigation for thyroid disease, whereas 32 (24.1%) of 133 patients were examined for thyroid disease after PET. Nineteen were found with autoimmune thyroiditis or hypothyroidism, and replacement therapy was initiated in 12. No significant correlation was found between maximum standardized uptake value and TSH (P = 0.09) or TPO antibody (P = 0.68) levels.

CONCLUSION

The incidental finding of increased (18)F-FDG uptake in the thyroid gland is associated with chronic lymphocytic (Hashimoto's) thyroiditis and does not seem to be affected by thyroid hormone therapy. SUV correlated neither with the degree of hypothyroidism nor with the titer of TPO antibodies.

The value of quantifying 18F-FDG uptake in thyroid nodules found incidentally on whole-body PET–CT

OBJECTIVE

To determine if quantification of [18F]fluorodeoxyglucose (18F-FDG) uptake in a thyroid nodule found incidentally on whole-body 18F-FDG positron emission tomography-computed tomography (PET-CT) can be used to discriminate between malignant and benign aetiology.

METHODS

A retrospective review of all patients with focally high uptake in the thyroid as an incidental finding on 18F-FDG PET-CT from May 2003 through May 2006. The uptake in the nodules was quantified using the maximum standardized uptake value (SUVmax). The aetiology was determined by cytology and/or ultrasound, or on histopathology.

RESULTS

Incidental focally high uptake was found in 79/7347 patients (1.1%). In 31/48 patients with adequate follow-up, a benign aetiology was determined. Median SUVmax for the benign group was 5.6, range 2.5-53. Malignancy was confirmed in 15/48 patients. The malignancies were papillary thyroid carcinoma in 12, metastasis from squamous cell carcinoma in one, and lymphoma in two. Median SUVmax for the malignant lesions was 6.4, range 3.5-16. Cytology suspicious for follicular carcinoma was found in 2/48 patients. No statistical difference (P=0.12) was found among the SUVmax between the benign and malignant groups.

CONCLUSION

Focally high uptake of 18F-FDG in the thyroid as an incidental finding occurred in 1.1% of the patients. Malignancy was confirmed or was suspicious in 17/48 (35%) of the patients that had adequate follow-up. There was no significant difference in the SUVmax between benign and malignant nodules.

Acetazolamide effect on cerebellar blood flow in crossed cerebral-cerebellar diaschisis

We studied the effect of acetazolamide on cerebellar blood flow in 11 stroke patients with large, unilateral cerebral hemispheric infarcts and no evidence of cerebellar infarction, but with cerebrocerebellar diaschisis of cerebral blood flow. Blood flow was determined with xenon-133 inhalation and dynamic single-photon emission computed tomography at rest and 20 minutes after the intravenous injection of 1.0 g acetazolamide. After acetazolamide, the mean +/- SD increases in blood flow in the affected and contralateral cerebellar hemispheres were 11.1 +/- 3.7 and 12.0 +/- 5.3 ml/100 g/min, respectively; the difference between hemispheres was not significant. The absolute increase in cerebellar flow in these 11 patients was of the same magnitude as that in 12 healthy controls. We conclude that cerebellar vasoreactivity is intact in stroke patients with crossed cerebrocerebellar diaschisis of cerebral blood flow. Our results lend further support to the concept that reduced cerebellar blood flow is secondary to functional deactivation. Our patients were studied 2 weeks to 5 years after their stroke, indicating that this phenomenon may be persistent.

Point-spread function reconstructed PET images of sub-centimeter lesions are not quantitative

Background

PET image reconstruction methods include modeling of resolution degrading phenomena, often referred to as point-spread function (PSF) reconstruction. The aim of this study was to develop a clinically relevant phantom and characterize the reproducibility and accuracy of high-resolution PSF reconstructed images of small lesions, which is a prerequisite for using PET in the prediction and evaluation of responses to treatment.

Sets of small homogeneous ¹⁸F-spheres (range 3–12 mm diameter, relevant for small lesions and lymph nodes) were suspended and covered by a ¹¹C-silicone, which provided a scattering medium and a varying sphere-to-background ratio. Repeated measurements were made on PET/CT scanners from two vendors using a wide range of reconstruction parameters. Recovery coefficients (RCs) were measured for clinically used volume-of-interest definitions.

Results

For non-PSF images, RCs were reproducible and fell monotonically as the sphere diameter decreased, which is the expected behavior. PSF images converged slower and had artifacts: RCs did not fall monotonically as sphere diameters decreased but had a maximum RC for sphere sizes around 8 mm, RCs could be greater than 1, and RCs were less reproducible. To some degree, post-reconstruction filters could suppress PSF artifacts.

Conclusions

High-resolution PSF images of small lesions showed artifacts that could lead to serious misinterpretations when used for monitoring treatment response. Thus, it could be safer to use non-PSF reconstruction for quantitative purposes unless PSF reconstruction parameters are optimized for the specific task.

Electronic supplementary material

The online version of this article (doi:10.1186/s40658-016-0169-9) contains supplementary material, which is available to authorized users.

Diffusion-weighted MRI compared to FDG PET/CT for assessment of early treatment response in lymphoma

BACKGROUND

18F fluoro-deoxyglucose (FDG) positron emission tomography / computed tomography (PET/CT) is a well-recognized diagnostic tool used for staging and monitoring of therapy response for lymphomas. During the past decade diffusion-weighted (DW) magnetic resonance imaging (MRI) is increasingly being included in the assessment of tumor response for various cancers.

PURPOSE

To compare the change in maximum standardized uptake value (ΔSUVmax) from FDG PET/CT with the change in apparent diffusion coefficient (ΔADC) from DW MRI after initiation of the first cycle of chemotherapy in patients with Hodgkin's lymphoma (HL) and in patients with diffuse large B-cell lymphoma (DLBCL).

MATERIAL AND METHODS

Twenty-seven consecutive patients with histologically proven lymphoma and lymphomatous lymph nodes (LLN) of the neck (19 with HL, 8 with DLBCL) underwent FDG PET/CT and MRI of the neck before and after initiation of the first cycle of chemotherapy. The mean time interval from initiation of chemotherapy to imaging was 19 days and 2 days for FDG PET/CT and MRI, respectively. For each patient ΔSUVmax, ΔADC, and change in volume of the same LLN were compared.

RESULTS

There was a significant mean decrease of SUVmax by 70%, but no significant change in ADC. There was no significant reduction in LLN volume.

CONCLUSION

There was no significant correlation between ΔSUVmax and ΔADC. Thus, our data do not support that FDG PET/CT can be replaced by early DW MRI for response evaluation in lymphoma patients.

Integrin scintimammography using a dedicated breast imaging, solid-state gamma-camera and (99m)Tc-labelled NC100692

OBJECTIVE

Integrin scintimammography with NC100692 and a dedicated gamma-camera, LumaGEM, based on semi-conductor technology, was performed to investigate the detection ability of this combination in breast cancer.

METHODS

Eight patients with a high suspicion of breast cancer were administered 600-750 MBq (99m)Tc-labelled NC100629. Two acquisitions using a cranio-caudal and a lateral view were used, with moderate compression of the breast.

RESULTS

LumaGEM scintigraphy revealed 9 of 11 malignancies, sized 6-20 mm. Two lesions in patients with multicentric disease were not diagnosed, one of which measured only 2.5 mm. In one patient, the procedure was inconclusive, due to major breast hypertrophy.

CONCLUSION

The combined use of NC100629 and a dedicated gamma-camera for breast imaging was highly effective in diagnosing breast cancer.

Synchronous and metachronous skeletal osteosarcomas: the Norwegian Radium Hospital experience

Background. The purpose of this work was to study clinical and histopathological tumor characteristics of patients treated for synchronous or metachronous skeletal osteosarcoma at The Norwegian Radium Hospital from January 1, 1980 to January 1, 2008. Patients and methods. The hospital sarcoma database and patient records were reviewed to identify cases with synchronous or metachronous skeletal osteosarcoma. Patients with more than one skeletal lesion in the absence of pulmonary or other soft tissue tumor manifestations were included in the study, and histopathological slides from these tumors were reviewed. Results. Among a total of 297 registered osteosarcoma patients, six with synchronous (2.0%) and 10 with metachronous (3.4%) skeletal osteosarcomas were identified. All tumors were of high-grade malignancy. Treatment at the time of the first osteosarcoma diagnosis was in most cases wide resections and multi-agent chemotherapy according to international protocols, whereas the treatment for metachronous tumors was individualized and in general much less intensive. One patient was diagnosed with Li-Fraumeni syndrome, two other individuals may be suspected to have the same syndrome, and yet another patient had previously been treated for a bilateral retinoblastoma. Thirteen patients are dead, 11 from metastatic osteosarcoma, one from myelodysplastic syndrome, and one from wound infection and methotrexate-related nephrotoxicity; whereas three patients are still alive with no evidence of osteosarcoma. Conclusions. The prognosis for patients with synchronous and metachronous skeletal osteosarcoma is poor. However, because long-term survival is seen, aggressive treatment to selected cases, e.g., patients with an osteosarcoma predisposing syndrome and/or late occurring metachronous tumours, is justified. Revealing a possible clonal relationship between these tumors, e.g., by karyotyping, may be of interest for estimating prognosis and guide therapy intensiveness.

Dose painting for re-irradiation of head and neck cancer

BACKGROUND

For patients with recurrent or second primary disease, re-irradiation can be challenging due to overlap with previously irradiated volumes. Dose painting may be attractive for these patients, as the focus is on delivering maximal dose to areas of high tumor activity. Here, we compare dose painting by contours (DPBC) treatment plans based on ¹⁸F-fluorodeoxyglucose (FDG) positron emission tomography (PET) with conventional plans.

MATERIAL AND METHODS

We included 10 patients with recurrent or second primary head and neck cancer (HNC) eligible for re-irradiation. Our conventional re-irradiation regimen is hyperfractionated radiotherapy 1.5 Gy twice daily over 4 weeks, giving a total dose of 60 Gy. For DPBC, we defined two prescription volumes, PV33 and PV66, corresponding to 33 and 66% of the highest FDG uptake in the tumor. The clinical target volume (CTV) prescription dose was 60 Gy, PV33; 65-67 Gy and PV66; 70-73 Gy. The DPBC plan is to be given the first 20 fractions and the conventional plan the last 20 fractions. Dose to organs at risk (OARs) were compared for DPBC and conventional treatment. By summation of the initial curative plan and the re-irradiation plan, we also evaluated differences in dose to the 2 ccm hot spot (D_2cc).

RESULTS

We achieved DPBC plans with adequate target coverage for all 10 patients. There were no significant differences in OAR doses between the standard plans and the DPBC plans (p=.7). Summation of the initial curative plan and the re-irradiation plan showed that the median D_2cc increased from 130 Gy (range 113-132 Gy; conventional) to 140 Gy (range 115-145 Gy; DPBC).

CONCLUSIONS

Our proposed DPBC could be straightforwardly implemented and all plans met the objectives. Re-irradiation of HNC with DPBC may increase tumor control without more side effects compared to conventional radiotherapy.

Perceived misinterpretation rates in oncologic 18F-FDG PET/CT studies: a survey of referring physicians

Because only pathologic examination can confirm the presence or absence of malignant disease in cancer patients, a certain rate of misinterpretation in any kind of imaging study is inevitable. For the accuracy of interpretation to be improved, determination of the nature, causes, and magnitude of this problem is needed. This study was designed to collect pertinent information from physicians referring patients for oncologic (18)F-FDG PET/CT.

METHODS

A total of 662 referring physicians completed an 11-question survey focused on their experience with the interpretation of oncologic (18)F-FDG PET/CT studies. The participants were oncologists (36.1%; n = 239), hematologists (14.5%; n = 96), radiation oncologists (7.4%; n = 49), surgeons (33.8%; n = 224), and other physicians (8.2%; n = 54). Questions were aimed at determining the frequency, nature, and causes of scan misinterpretations as well as potential solutions to reduce the frequency of misinterpretations.

RESULTS

Perceived misinterpretation rates ranged from 5% to 20%, according to most (59.3%) of the participants; 20.8% of respondents reported rates of less than 5%. Overinterpretation rather than underinterpretation was more frequently encountered (68.9% vs. 8.7%, respectively). Limited availability of a patient's history and limited experience of interpreters were the major contributors to this phenomenon, according to 46.8% and 26.7% of the participants, respectively. The actions most commonly suggested to reduce misinterpretation rates (multiple suggestions were possible) were the institution of multidisciplinary meetings (59.8%), the provision of adequate history when ordering an examination (37.4%), and a discussion with imaging specialists when receiving the results of the examination (38.4%).

CONCLUSION

Overinterpretation rather than underinterpretation of oncologic (18)F-FDG PET/CT studies prevails in clinical practice, according to referring physicians. Closer collaboration of imaging specialists with referring physicians through more multidisciplinary meetings, improved communication, and targeted training of interpreting physicians are actions suggested to reduce the rates of misinterpretation of oncologic (18)F-FDG PET/CT studies.

Sentinel node procedure in low-stage/low-grade penile carcinomas

OBJECTIVE

To optimize the indication for sentinel lymph node (SLN) biopsy according to tumour size in penile carcinoma.

MATERIAL AND METHODS

This was a retrospective analysis of 23 consecutive patients (median age 65 years; range 49-85 years) with primary penile carcinoma classified according to the TNM classification as stage T1-T3 who were identified as having SLNs in the groins. SLNs were detected by means of preoperative injection of a 99mTc nanocolloid around the tumour and peroperative use of a gamma detector probe. The average tumour size was 2.9+/-1.3 cm.

RESULTS

In 7/25 patients with penile carcinoma examined with the SLN method, metastases to inguinal lymph nodes could be demonstrated. Two out of three patients with primary penile carcinomas classified as T1 according to the TNM classification and tumours > 3 cm in diameter had inguinal lymph node metastases. One of the patients had a micrometastasis, which was detected by means of immunohistochemical analysis. Seven out of eight patients with penile carcinomas > 3 cm in diameter had lymph node metastases. We did not observe any major surgical complications associated with the SLN procedure.

CONCLUSION

These data indicate that penile carcinomas with a diameter of >3 cm should be investigated with SLN biopsy regardless of stage. However, multicentre studies are needed in order to obtain the appropriate number of patients.

A comparison of FDG PET/MR and PET/CT for staging, response assessment, and prognostic imaging biomarkers in lymphoma

The aim of the current study was to investigate the diagnostic performance of FDG PET/MR compared to PET/CT in a patient cohort including Hodgkins lymphoma, diffuse large B-cell lymphoma, and high-grade B-cell lymphoma at baseline and response assessment. Sixty-one patients were examined with FDG PET/CT directly followed by PET/MR. Images were read by two pairs of nuclear medicine physicians and radiologists. Concordance for lymphoma involvement between PET/MR and the reference standard PET/CT was assessed at baseline and response assessment. Correlation of prognostic biomarkers Deauville score, criteria of response, SUVmax, SUVpeak, and MTV was performed between PET/MR and PET/CT. Baseline FDG PET/MR showed a sensitivity of 92.5% and a specificity 97.9% compared to the reference standard PET/CT (κ 0.91) for nodal sites. For extranodal sites, a sensitivity of 80.4% and a specificity of 99.5% were found (κ 0.84). Concordance in Ann Arbor was found in 57 of 61 patients (κ 0.92). Discrepancies were due to misclassification of region and not lesion detection. In response assessment, a sensitivity of 100% and a specificity 99.9% for all sites combined were found (κ 0.92). There was a perfect agreement on Deauville scores 4 and 5 and criteria of response between the two modalities. Intraclass correlation coefficient (ICC) for SUVmax, SUVpeak, and MTV values showed excellent reliability (ICC > 0.9). FDG PET/MR is a reliable alternative to PET/CT in this patient population, both in terms of lesion detection at baseline staging and response assessment, and for quantitative prognostic imaging biomarkers.

A gel tumour phantom for assessment of the accuracy of manual and automatic delineation of gross tumour volume from FDG-PET/CT

INTRODUCTION

Our primary aim was to make a phantom for PET that could mimic a highly irregular tumour and provide true tumour contours. The secondary aim was to use the phantom to assess the accuracy of different methods for delineation of tumour volume from the PET images.

MATERIAL AND METHODS

An empty mould was produced on the basis of a contrast enhanced computed tomography (CT) study of a patient with a squamous cell carcinoma in the head and neck region. The mould was filled with a homogeneous fast-settling gel that contained both (18)F for positron emission tomography (PET) and an iodine contrast agent. This phantom (mould and gel) was scanned on a PET/CT scanner. A series of reference tumour contours were obtained from the CT images in the PET/CT. Tumour delineation based on the PET images was achieved manually, by isoSUV thresholding, and by a recently developed three-dimensional (3D) Difference of Gaussians algorithm (DoG). Average distances between the PET-derived and reference contours were assessed by a 3D distance transform.

RESULTS

The manual, thresholding and DoG delineation methods resulted in volumes that were 146%, 86% and 100% of the reference volume, respectively, and average distance deviations from the reference surface were 1.57 mm, 1.48 mm and 1.0, mm, respectively.

DISCUSSION

Manual drawing as well as isoSUV determination of tumour contours in geometrically irregular tumours may be unreliable. The DoG method may contribute to more correct delineation of the tumour. Although the present phantom had a homogeneous distribution of activity, it may also provide useful knowledge in the case of inhomogeneous activity distributions.

CONCLUSION

The geometric irregular tumour phantom with its inherent reference contours was an important tool for testing of different delineation methods and for teaching delineation.

Comparison of three cold kit reconstitution techniques for the reduction of hand radiation dose

In the performance of conventional nuclear pharmacy work, personnel usually receive the highest hand radiation dose during reconstitution of 99Tcm-labelled radiopharmaceuticals. This study was conducted to compare the hand radiation doses incurred during the preparation of 99Tcm-labelled radiopharmaceuticals using three different reconstitution procedures: (1) the standard reconstitution method (i.e. withdrawing 99Tcm activity and normal saline [NS] into the same syringe before adding to the cold kit) (standard); (2) an alternative reconstitution procedure using two syringes to add normal saline separately before 99Tcm activity to the cold kit (NS/Tc); and (3) a standard reconstitution procedure using a robotic system (Amercare Syringe Fill Station, model NuMed SFS 3a, Amercare Ltd, Oxon, UK) (robot). Radiation doses were monitored by thermoluminescent dosimeters (Landauer Inc., Glenwood, IL, USA) on the base of the fourth finger (i.e. ring finger) of the non-dominant hand and on the mid-portion of the second finger (i.e. index finger) of the dominant hand. Three sets of ring badges were measured for each procedure, with 10 stimulated or real reconstitutions per set. Two different radiopharmaceutical kits were evaluated: 99Tcm-MDP, as it is the most frequently used radiopharmaceutical in the majority of nuclear medicine departments (all three reconstitution methods; i.e. standard, NS/Tc and robot), and 99Tcm-sestamibi, as it is not only reconstituted with the highest amount of radioactivity but is also the most frequently dispensed radiopharmaceutical in our laboratory (standard and robot). All kits were prepared from an elution vial containing a standardized amount of 99Tcm activity (i.e. 104.4 +/- 3.6 GBq). To each of the cold MDP and sestamibi kits, 20.7 +/- 1.2 GBq and 44.2 +/- 0.7 GBq of 99Tcm activity were added, respectively. Average accumulated radiation doses for 10 reconstitutions to the fingers (non-dominant/dominant) for the preparations of 99Tcm-MDP were as follows: 14.2 +/- 0.9 mSv/2.8 +/- 0.8 mSv (standard), 10.0 +/- 0.6 mSv/2.7 +/- 0.2 mSv (NS/Tc), and 0.6 +/- 0.1 mSv/1.3 +/- 0.1 mSv (robot). For 99Tcm-sestamibi, the average accumulated radiation doses for 10 reconstitutions to the fingers (non-dominant/dominant) were 6.7 +/- 0.7 mSv/4.6 +/- 0.5 mSv (standard) and 1.1 +/- 0.1 mSv/3.1 +/- 0.4 mSv (robot). When compared to the standard reconstitution method, our results show that the NS/Tc method slightly reduced radiation dose to the non-dominant hand, without any significant reduction for the dominant hand. However, the robot has proved to be the most effective method to considerably reduce radiation dose to both hands. A robotic system should be a useful ALARA (as low as reasonably achievable) tool to prepare other high-activity 99Tcm-labelled radiopharmaceuticals, as well as therapeutic and PET radiopharmaceuticals.

123I Scan With Whole-Body Retention Measurement at 48 Hours for Simplified Dosimetry Before 131I Treatment of Metastatic Thyroid Cancer

ABSTRACT

A previously published model (Atkins) allows for calculation of 131I maximum tolerated activity on the basis of 48-hour whole-body retention of 131I on a pretherapy diagnostic scan. Our practice uses iodine 123I for diagnostic imaging of metastatic thyroid cancer for staging before 131I therapy, with images typically acquired 24 hours after administration of the radiopharmaceutical. We explored the feasibility of an additional 123I whole-body scan and retention measurement at 48 hours, with application of the model to estimate maximum tolerated activity of radioiodine before 131I treatment of metastatic thyroid cancer.

Effects of alternative reconstitution procedures on the labelling efficiency and in vitro stability of 99Tcm-labelled radiopharmaceuticals

Adding normal saline (NS) separately before 99Tcm-sodium pertechnetate to MDP cold kits has been shown to reduce substantially the radiation dose to the hand. A similar dose reduction will probably prove to be valid with the preparation of most other 99Tcm-labelled radiopharmaceuticals. However, it is unknown how this altered reconstitution procedure may affect the labelling efficiency and in vitro stability of the 99Tcm-labelled radiopharmaceuticals. We have evaluated the effects on the labelling efficiency and in vitro stability of 99Tcm-labelled MDP, mertiatide and sestamibi reconstituted with three different methods: adding normal saline before 99Tcm activity (NS/Tc); adding 99Tcm activity before normal saline (Tc/NS); and the standard reconstitution method of adding both 99Tcm activity and normal saline together. The labelling efficiency and in vitro stability were evaluated by measuring the radiochemical purity of each radiopharmaceutical tested at 0, 1, 3, 6, 12 (except 99Tcm-MDP) and 24 h after reconstitution. For 99Tc-mertiatide, there was a very slight difference in the labelling efficiency, mostly due to the Tc/NS method being approximately 0.29% lower across time post-reconstitution than the standard method. For 99Tcm-labelled MDP and sestamibi, there were no differences between the three methods in terms of labelling efficiency and in vitro stability. In conclusion, both alternative methods (i.e. NS/Tc and Tc/NS) appear not to have any detrimental effect on the labelling efficiency and in vitro stability of the 99Tcm-labelled radiopharmaceuticals that we tested. However, of the two alternative kit reconstitution methods, we recommend the NS/Tc method, since it may reduce the hand radiation dose.

Effects of photon attenuation on the determination of cardiac volumes from reconstructed counts in gated blood pool SPET

In gated cardiac blood pool single-photon emission tomography (SPET), the volume of a ventricle may be determined by a method that exploits the proportionality between that volume and the total reconstructed counts within a larger volume of interest that includes the actual ventricle. The present work was carried out to determine how the attenuation of photons modifies the reconstructed counts obtained with this technique, and how this affects the accuracy of volume determination. Furthermore, we wanted to investigate how count-based determination of ventricle volumes is affected by the total SPET rotation angle and by different arm positions. We used micro -maps derived from computed tomography (CT) series of nine arbitrarily chosen patients to calculate a volume correction factor for each cardiac volume manually drawn on the CT images. An anthropomorphic chest phantom was used to confirm the calculation of correction factors. For the regions of the ventricles contained within a CT slice through the central part of the heart, the left to right volume ratio needed to be corrected by factors of 1.21 and 1.12 for 180 degrees and 360 degrees rotation, respectively. When all voxels within the left and right ventricles were included, the required volume ratio correction factor was close to 1. However, the variation among patients was larger for a 180 degrees (range 0.97-1.08) than for a 360 degrees rotation arc (range 1.0-1.03).

A phantom for investigation of tumour signal and noise in PET reconstruction with various smoothing filters: experiments and comparisons with simulated intensity diffusion

An abdomen phantom, containing an idealised fillable liver volume was developed. A fast settling gel was used to produce a row of simulated tumours as well as normal surrounding tissue, each of these components containing different concentrations of (18)F-FDG. The magnitude of the signal above normal tissue intensity as well as the noise was obtained after reconstructions with Ordered Subset expectation-maximization (OSEM) and various Gaussian smoothing filters. Signals derived by 'simulated intensity diffusion' agreed well with experimental results.

Oncologic PET/CT interpretation and reporting approaches. Survey in clinical practice

AIM

To elucidate techniques most commonly used for interpreting oncologic PET/CT studies. This survey forms a basis to work on standardization of reporting and highlight the most important issues to be addressed.

METHODS

A web-based survey of 329 PET/CT imaging specialists was designed with the intent to determine image interpretation patterns. The questionnaire consisted of 19 questions. Of the 329 participants, 230 were nuclear medicine specialists, 46 were radiologists, and 53 had dual-board certification.

RESULTS

Report ofstandardized uptake values (SUV) is not consistent;only50.2% of respondents always report SUVs, while 45.2% report only if needed or requested. 80.9% of respondents indicated that reporting of SUV is only appropriate when its limitations are understood whereby a large majority prefer to report SUVmax. Maximum intensity projection (MIP) images are almost always reviewed by 91.1% of the respondents. An accurate and detailed clinical history is considered an essential element for reading PET/CT studies by 84.0%, but only 20.7% report that this is always available. The most common self-reported average time for reviewing and reporting of whole body PET/CT (with no prior comparison scan) was 15-20 min (27.5%).

CONCLUSION

PET readers have considerable reservations regarding the use and reporting of SUVs. SUVmax is more frequently used than SUVmean. Evaluation of MIP images is considered an important element of PET/CT interpretation. Although availability of sufficient patient's history is considered essential, this is rarely available.

Multisite experience of fluciclovine (18F) PET/CT imaging in biochemically recurrent prostate cancer: Impact of clinical factors and intersite variation

163

Background: Fluciclovine (18F) is an FDA-approved positron emission tomography/computerized tomography (PET/CT) tracer in clinical use for the detection and localization of biochemically recurrent (BCR) prostate cancer. Here, we report the impact of clinical factors and study site on its performance. Methods: In total, 596 subjects with BCR prostate cancer underwent fluciclovine (18F) PET/CT scanning at four sites in Italy, Norway and USA. Detection Rates (DR), including region level analyses, were stratified by prostate specific antigen (PSA) levels, PSA doubling time (PSAdt), Gleason score (GS), and by investigator/site. Extra-prostatic disease was defined as all positivity outside of residual prostate, prostate bed and seminal vesicles. Results: Fluciclovine (18F) PET/CT was positive in 67.7% (403/595) of subjects. Positive findings were detected in the prostate/bed and pelvic lymph node regions in 38.7% (232/599) and 32.6% (194/596) of scans, respectively. Metastatic involvement outside the pelvis was found in 26.2% (155/591) of scans. Generally, DR increased with increasing baseline PSA (Table 1). While subject level DR did not vary significantly with PSAdt (DR = 60-69% across all categories), a positive extra-prostatic scan was more likely in patients with shorter PSAdt (DR = 52%, 48%, 37% and 28% for PSAdt <3, 3-<6, 6-<12 and >12 months, respectively). Among 361 subjects for whom baseline GS was available, scores ≥9 were associated with the highest extra-prostatic DR (55%) compared with 23% in patients with GS ≤6. Inter-site variations in acquisition protocols may have impacted DR at low baseline PSA values; with subject level DR at PSA >0.2-0.5 ng/ml = 20%, 38%, 46% and 73% at site A, B, C and D, respectively. Conclusions: Fluciclovine (18F) can detect and localize BCR prostate cancer in a wide range of subjects and, with appropriate imaging protocols, has a clinically useful DR at PSA <0.5 ng/ml. Clinical trial information: NCT02443571. [Table: see text]

Characterization of an asymmetric add-on collimator used with a hand-held gamma probe for radioguided surgery and sentinel node detection: a demonstration of an alternative collimation method

OBJECTIVE

The aim of the study was to investigate a new principle for collimation of gamma probes for radioguided surgery and sentinel node detection: the use of asymmetric lateral shielding. The intension was to maintain the sensitivity in the lateral and forward directions on the unshielded side while at the same time to shield the probe against high activity sources that could mask the signal from the object to be detected.

METHODS

The device was constructed to shield only against photons that come from a region in space that spans approximately 180° sideways and forwards relative to the detector. The intension of the study was to demonstrate the principle rather than to document its use in the clinic. Sensitivity profiles were derived from measurements obtained while stepwise moving the probe relatively to a point source of known activity surrounded by water. The measurements were taken in the symmetry plane of the collimator where the shielding effects were expected to be most pronounced.

RESULTS

The asymmetric collimator led to nearly unchanged sensitivity in the lateral and forward directions. At the same time, the field of view was effectively shrunk on the shielded side. Contributions from sources lateral and close to the shield were reduced by factors up to 45.

CONCLUSION

By rotating the probe around its longitudinal axis, an asymmetric add-on shield collimator could potentially make it easier to detect a sentinel node when this is located close to a neighbouring high activity region like the urinary bladder or the injection site.

[Diagnosis of type 2 diabetes in general practice]

Among 285 patients seen in general practice, all over the age of 40, 11 (4%) new cases of non-insulin-dependent diabetes mellitus was diagnosed. 12 patients (4%) were found to have impaired glucose tolerance. Measurement of glucose levels in unstandardized blood samples is a suitable method of screening for non-insulin-dependent diabetes in general practice. In order to reduce the number of oral glucose tolerance tests we suggest a modification of WHO guidelines.