Positron emission tomography (PET) imaging enables quantitative assessment of tissue physiology. Dynamic pharmacokinetic analysis of PET images requires accurate estimation of the radiotracer plasma ...input function to derive meaningful parameter estimates, and small discrepancies in parameter estimation can mimic subtle physiologic tissue variation. This study evaluates the impact of input function interpolation method on the accuracy of Patlak kinetic parameter estimation through simulations modeling the pharmacokinetic properties of 68Ga-PSMA-11. This study evaluated both trained and untrained methods. Although the mean kinetic parameter accuracy was similar across all interpolation models, the trained node weighting interpolation model estimated accurate kinetic parameters with reduced overall variability relative to standard linear interpolation. Trained node weighting interpolation reduced kinetic parameter estimation variance by a magnitude approximating the underlying physiologic differences between normal and diseased prostatic tissue. Overall, this analysis suggests that trained node weighting improves the reliability of Patlak kinetic parameter estimation for 68Ga-PSMA-11 PET.
Summary Background Plexiform neurofibromas are slow-growing chemoradiotherapy-resistant tumours arising in patients with neurofibromatosis type 1 (NF1). Currently, there are no viable therapeutic ...options for patients with plexiform neurofibromas that cannot be surgically removed because of their proximity to vital body structures. We undertook an open-label phase 2 trial to test whether treatment with imatinib mesylate can decrease the volume burden of clinically significant plexiform neurofibromas in patients with NF1. Methods Eligible patients had to be aged 3–65 years, and to have NF1 and a clinically significant plexiform neurofibroma. Patients were treated with daily oral imatinib mesylate at 220 mg/m2 twice a day for children and 400 mg twice a day for adults for 6 months. The primary endpoint was a 20% or more reduction in plexiform size by sequential volumetric MRI imaging. Clinical data were analysed on an intention-to-treat basis; a secondary analysis was also done for those patients able to take imatinib mesylate for 6 months. This trial is registered with ClinicalTrials.gov , number NCT01673009. Findings Six of 36 patients (17%, 95% CI 6–33), enrolled on an intention-to-treat basis, had an objective response to imatinib mesylate, with a 20% or more decrease in tumour volume. Of the 23 patients who received imatinib mesylate for at least 6 months, six (26%, 95% CI 10–48) had a 20% or more decrease in volume of one or more plexiform tumours. The most common adverse events were skin rash (five patients) and oedema with weight gain (six). More serious adverse events included reversible grade 3 neutropenia (two), grade 4 hyperglycaemia (one), and grade 4 increases in aminotransferase concentrations (one). Interpretation Imatinib mesylate could be used to treat plexiform neurofibromas in patients with NF1. A multi-institutional clinical trial is warranted to confirm these results. Funding Novartis Pharmaceuticals, the Indiana University Simon Cancer Centre, and the Indiana University Herman B Wells Center for Pediatric Research.
The authentic standards GSK1482160 and its isomer, as well as the radiolabeling precursors desmethyl-GSK1482160 and Boc-protected desmethyl-GSK1482160 were synthesized from L-pyroglutamic acid, ...methyl L-pyroglutamate and 2-chloro-3-(trifluoromethyl)benzylamine with overall chemical yield 27-28% in 3 steps, 58% in 4 steps, 76% in 1 step and 33% in 2 steps, respectively. (11)CGSK1482160 was prepared from either desmethyl-GSK1482160 or Boc-protected desmethyl-GSK1482160 with (11)CCH3OTf through N-(11)Cmethylation and isolated by HPLC combined with SPE in 40-50% and 30-40% radiochemical yield, respectively, based on (11)CCO2 and decay corrected to end of bombardment (EOB). The radiochemical purity was >99%, and the specific activity at EOB was 370-1110 GBq/μmol with a total synthesis time of ∼40-min from EOB.
Purpose of Review
This review will explore the latest in advanced imaging techniques, with a focus on the complementary nature of multiparametric, multimodality imaging using magnetic resonance ...imaging (MRI) and positron emission tomography (PET).
Recent Findings
Advanced MRI techniques including perfusion-weighted imaging (PWI), MR spectroscopy (MRS), diffusion-weighted imaging (DWI), and MR chemical exchange saturation transfer (CEST) offer significant advantages over conventional MR imaging when evaluating tumor extent, predicting grade, and assessing treatment response. PET performed in addition to advanced MRI provides complementary information regarding tumor metabolic properties, particularly when performed simultaneously.
18
F-fluoroethyltyrosine (FET) PET improves the specificity of tumor diagnosis and evaluation of post-treatment changes. Incorporation of radiogenomics and machine learning methods further improve advanced imaging.
Summary
The complementary nature of combining advanced imaging techniques across modalities for brain tumor imaging and incorporating technologies such as radiogenomics has the potential to reshape the landscape in neuro-oncology.
We evaluated which lesions are detected and missed on
GaGa-PSMA (prostate specific membrane antigen)-11 positron emission tomography in patients with primary prostate cancer.
Patients undergoing ...radical prostatectomy were enrolled in this prospective observational study. Patients underwent
GaGa-PSMA-11 positron emission tomography/computerized tomography or positron emission tomography/magnetic resonance imaging prior to surgery and received a dose of
GaGa-PSMA-11 intraoperatively for positron emission tomography of extirpated specimens. Whole mount pathology was performed with lesion and intralesion based analysis to determine the characteristics of lesions detected or not detected by PSMA positron emission tomography. Lesion volume was determined by planimetry and clinically significant lesion volume was calculated as lesion volume × fraction pattern 4/5.
On whole mount analysis 30 cancerous lesions were found in a total of 15 patients, including 4, 15, 4, 1 and 6 which were Grade Group 1, 2, 3, 4 and 5, respectively. PSMA-positron emission tomography detected 100% of primary/index lesions and 8 of 11 (82%) secondary lesions. All Grade Group 3-5 lesions were detected vs 12 of 15 Grade Group 2 lesions. When comparing Grade Group 2 vs 3-5, lesion size was similar (p=0.48) but the standardized uptake value was lower for Grade Group 2 vs 3-5 (5.3 vs 7.9, p=0.03). The 3 missed lesions showed 10% or less of pattern 4 and a Gleason pattern 4/5 volume of less than 0.1 cm
.
PSMA positron emission tomography detected 100% of primary/index lesions in this study. The 3 missed secondary lesions were small and had a low percent of pattern 4. This argues for further study to better understand what defines clinically significant prostate cancer, which would assist in determining whether small lesions that become challenging to detect by
GaGa-PSMA-11 positron emission tomography confer a risk to the patient.
Traditional quantitative perfusion imaging methods require complex data acquisition and analysis strategies; typically require ancillary arterial blood sampling for measurement of input functions; ...are limited to single organ or tissue regions in an imaging session; and because of their complexity, are not well suited for routine clinical implementation in a standardized fashion that can be readily repeated across diverse clinical sites. The whole-body perfusion method described in this chapter has the advantages of on-demand radiotracer production; simple tissue pharmacokinetics enabling standardized estimation of perfusion; short-lived radionuclides, facilitating repeat or combination imaging procedures; and scalability to support widespread clinical implementation. This method leverages the unique physiological characteristics of radiolabeled copper(II) bis(thiosemicarbazone) complexes and the detection sensitivity of positron emission tomography (PET) to produce quantitatively accurate whole-body perfusion images. This chapter describes the synthesis of ethylglyoxal bis(thosemicarbazonato)copper(II) labeled with copper-62 (
CuCu-ETS), its unique physiological characteristics, a simple tracer kinetic model for estimation of perfusion using image-derived input functions, and validation of the method against a reference standard perfusion tracer. A detailed description of the methods is provided to facilitate implementation of the perfusion imaging method in PET imaging facilities.
To prospectively evaluate the utility of dynamic contrast material-enhanced magnetic resonance (MR) imaging in predicting the response of locally advanced pancreatic cancer to combined chemotherapy ...and antiangiogenic therapy.
This prospective, institutional review board-approved, HIPAA-compliant study with informed consent assessed dynamic contrast-enhanced MR imaging in 11 patients (mean age, 54.3 years; six men and five women) with locally invasive pancreatic cancer before and 28 days after combined chemotherapy and antiangiogenic therapy. Axial perfusion images were obtained after injection of 0.1 mmol gadopentetate dimeglumine per kilogram of body weight. Sagittal images of the upper abdominal aorta were obtained for arterial input function calculation. A two-compartment kinetic model was used to calculate the perfusion parameters K(trans) (the rate constant that represents transfer of contrast agent from the arterial blood into the extravascular extracellular space), K(ep) (the rate constant that represents transfer of contrast agent from the extravascular extracellular space to the blood plasma), and volume of distribution (v(e)). Semiquantitative measurements, peak tissue gadolinium concentration (C(peak)), maximum slope of gadolinium increase (slope), and area under the gadolinium curve at 60 seconds (AUC(60)) were also calculated. Perfusion parameters and tumor size changes were correlated with carbohydrate antigen 19-9 levels. Comparisons between pre- and posttreatment studies were performed by using the Wilcoxon signed rank test, and comparisons between responders and nonresponders were performed by using the Mann-Whitney test.
After therapy, K(trans), v(e), C(peak), slope, and AUC(60) decreased significantly (P = .02, .001, .002, .007, and .01, respectively). Tumor size and K(ep) were not significantly changed. Pretreatment K(trans) and K(ep) were significantly higher (P = .02 and .006, respectively) in tumors that showed marker response than in those that did not. A pretreatment K(trans) value (milliliters of blood per milliliter of tissue times minutes) of more than 0.78 mL/mL . min was 100% sensitive and 71% specific for subsequent tumor response. Semiquantative parameters and tumor size were not different between the groups.
Pretreatment K(trans) measurement in pancreatic tumors can predict response to antiangiogenic therapy. All perfusion parameters showed substantial reduction after 28 days of combined chemotherapy and antiangiogenic therapy.
Background
68
Ga-PSMA-11 positron emission tomography enables the detection of primary, recurrent, and metastatic prostate cancer. Regional radiopharmaceutical uptake is generally evaluated in static ...images and quantified as standard uptake values (SUVs) for clinical decision-making. However, analysis of dynamic images characterizing both tracer uptake and pharmacokinetics may offer added insights into the underlying tissue pathophysiology. This study was undertaken to evaluate the suitability of various kinetic models for
68
Ga-PSMA-11 PET analysis. Twenty-three lesions in 18 patients were included in a retrospective kinetic evaluation of 55-min dynamic
68
Ga-PSMA-11 pre-prostatectomy PET scans from patients with biopsy-demonstrated intermediate- to high-risk prostate cancer. Three kinetic models—a reversible one-tissue compartment model, an irreversible two-tissue compartment model, and a reversible two-tissue compartment model, were evaluated for their goodness of fit to lesion and normal reference prostate time-activity curves. Kinetic parameters obtained through graphical analysis and tracer kinetic modeling techniques were compared for reference prostate tissue and lesion regions of interest.
Results
Supported by goodness of fit and information loss criteria, the irreversible two-tissue compartment model optimally fit the time-activity curves. Lesions exhibited significant differences in kinetic rate constants (
K
1
,
k
2
,
k
3
,
K
i
) and semiquantitative measures (SUV and %ID/kg) when compared with reference prostatic tissue. The two-tissue irreversible tracer kinetic model was consistently appropriate across prostatic zones.
Conclusions
An irreversible tracer kinetic model is appropriate for dynamic analysis of
68
Ga-PSMA-11 PET images. Kinetic parameters estimated by Patlak graphical analysis or full compartmental analysis can distinguish tumor from normal prostate tissue.
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