Biomedical subjects

Michael J Welch

Publications and source records attributed to Michael J Welch.

At least 19 recordsLinked to original sources

PubMed2007

Synthesis and biologic evaluation of 64Cu-labeled rhenium-cyclized alpha-MSH peptide analog using a cross-bridged cyclam chelator.

UNLABELLED: Early detection of cutaneous melanoma is essential, as prognosis with metastatic melanoma is poor. Previous studies showed that (64)Cu-DOTA-ReCCMSH(Arg(11)) (DOTA is 1,4,7,10-tetraazacyclododecane-N,N',N'',N'''-tetraacetic acid), a cyclic analog of alpha-melanocyte-stimulating hormone (alpha-MSH), has the potential for the detection of malignant melanoma using PET. However, (64)Cu-DOTA-ReCCMSH(Arg(11)) demonstrated high background in nontarget tissues due to the in vivo instability of the Cu-DOTA moiety. CBTE2A (CBTE2A is 4,11-bis(carboxymethyl)-1,4,8,11-tetraazabicyclo[6.6.2]hexadecane) has been shown to be a more stable copper chelate with improved in vivo stability, resulting in an improvement in clearance from nontarget tissues. The goal of this study was to conjugate CBTE2A to the alpha-MSH targeting ReCCMSH(Arg(11)) peptide for labeling to (64)Cu and to investigate whether the increased metal-chelate stability with CBTE2A would improve imaging quality. METHODS: The recyclized peptide CBTE2A-ReCCMSH(Arg(11)) was synthesized using a solid-phase peptide synthesizer followed by rhenium cyclization. In vivo characteristics of (64)Cu-CBTE2A-ReCCMSH(Arg(11)) were examined with small-animal PET and acute biodistribution studies in B16/F1 tumor-bearing mice. RESULTS: Biodistribution studies showed high and rapid receptor-mediated tumor uptake with values similar to those reported for (64)Cu- and (86)Y-labeled DOTA-ReCCMSH(Arg(11)). Nontarget organ concentration for (64)Cu-CBTE2A-ReCCMSH(Arg(11)) was considerably lower than that of the (64)Cu-DOTA analog, resulting in significantly higher tumor-to-nontarget tissue ratios. Compared with (86)Y-DOTA-ReCCMSH(Arg(11)), (64)Cu-CBTE2A-ReCCMSH(Arg(11)) demonstrated increased tumor retention and kidney clearance. Small-animal PET images showed that the tumor could be clearly visualized at all time points (0.5-24 h). CONCLUSION: Our data suggest the superior stability of the (64)Cu-CBTE2A moiety compared with (64)Cu-DOTA, making (64)Cu-CBTE2A-ReCCMSH(Arg(11)) an ideal candidate for the PET of malignant melanoma.

Animals↗

PubMed2006

Development and evaluation of a candidate reference measurement procedure for the determination of progesterone in human serum using isotope-dilution liquid chromatography/tandem mass spectrometry.

Progesterone is a steroid hormone that is involved in regulating female reproductive processes. Its concentration in blood is measured to determine ovarian function. A candidate reference measurement procedure for progesterone in human serum involving isotope dilution coupled with liquid chromatography/tandem mass spectrometry (LC/MS/MS) has been developed and critically evaluated. The progesterone along with its internal standard (progesterone-13C2) was extracted from the serum matrix using liquid-liquid extraction prior to reversed-phase LC/MS/MS. The accuracy of the measurement was evaluated by a comparison of results of this method on a lyophilized human serum reference material for progesterone [Certified Reference Material (CRM) 347] with the certified values determined by gas chromatography/mass spectrometry (GC/MS) reference methods and by a recovery study for the added progesterone. The results of this method for progesterone agreed with the certified value within the uncertainty of the measurements for the CRM 347. The recovery of the added progesterone ranged from 100.1 to 100.9%. This method was applied to the determination of progesterone in frozen serum samples from three individual female donors with the progesterone concentrations ranging from 0.151 to 24.42 ng/g. Excellent reproducibility was obtained with within-set coefficients of variation (CVs) ranging from 0.1 to 1.4%, and between-set CVs ranging from 0.3 to 0.5%. Excellent linearity was also obtained with correlation coefficients of all linear regression lines (measured intensity ratios vs mass ratios) ranging from 0.9998 to 1.0000. The detection limit at a signal-to-noise ratio of approximately 3 was 1.8 pg of progesterone. This well-characterized LC/MS/MS method for serum progesterone, which demonstrates good accuracy and precision, low susceptibility to interferences, and comparability with GC/MS reference methods, qualifies as a reference measurement procedure that can be used to provide an accuracy base to which routine methods for progesterone can be compared and that will serve as a standard of higher order for measurement traceability.

Chromatography, Liquid↗

PubMed2006

Synthesis, radiolabeling, and in vivo evaluation of an 18F-labeled isatin analog for imaging caspase-3 activation in apoptosis.

A non-peptide-based isatin sulfonamide analog, WC-II-89, was synthesized and its inhibition toward recombinant human caspase-3 and other caspases was determined. This compound showed high potency for inhibiting caspase-3 and -7, and high selectivity against caspases-1, -6, and -8. [(18)F]WC-II-89 was synthesized via a nucleophilic substitution of the corresponding mesylate precursor in high yield and radiochemical purity. Biodistribution studies using [(18)F]WC-II-89 revealed higher uptake in liver and spleen of cycloheximide-treated rats, an animal model of apoptosis, relative to control animals. Western blot analysis confirmed the presence of activated caspase-3 in the liver and spleen of cycloheximide-treated animals. MicroPET imaging studies revealed a high uptake of the radiotracer in the liver of a cycloheximide-treated rat relative to the untreated control. These data suggest that [(18)F]WC-II-89 is a potential radiotracer for imaging caspase-3 activation in tissues undergoing apoptosis.

Animals↗

PubMed2006

Bromine- and iodine-substituted 16alpha,17alpha-dioxolane progestins for breast tumor imaging and radiotherapy: synthesis and receptor binding affinity.

Progesterone receptors (PRs) are present in many breast tumors, and their levels are increased by certain endocrine therapies. We describe the synthesis and PR binding affinities of a series of bromine- and iodine-substituted 16alpha,17alpha-dioxolane progestins, some of which, when appropriately radiolabeled, are potential agents for diagnostic imaging of PR-positive breast tumors using positron emission tomography (PET) and for radiotherapy. These compounds were synthesized from halogenated furanyl, phenyl, and thiophenyl aldehydes and a progestin 16alpha,17alpha,21-triol (5) in the presence of HClO4 or Sc(OTf)3 in high yields under optimized conditions. A new reagent, perfluoro-1-butanesulfonyl fluoride (PBSF), was used to convert the C-21 OH to F in high yields. The relative binding affinities (RBAs) of the most promising compounds for the PR (RBA of R5020 = 100) were 16alpha,17alpha-[(R)-1'-alpha-(5-bromofurylmethylidene)dioxyl]-21-hydroxy-19-norpregn-4-ene-3,20-dione (endo-6; RBA = 65 and moderate lipophilicity), 21-fluoro-16alpha,17alpha-[(R)-1'-alpha-(5-iodofurylmethylidene)dioxyl]-19-norpregn-4-ene-3,20-dione (endo-14; RBA = 40) and 21-fluoro-16alpha,17alpha-[(S)-1'-beta-(4-iodophenylmethylidene)dioxyl]-19-norpregn-4-ene-3,20-dione (exo-16; RBA = 34).

Animals↗

PubMed2006

Synthesis and biological evaluation of a nonsteroidal bromine-76-labeled androgen receptor ligand 3-[76Br]bromo-hydroxyflutamide.

INTRODUCTION: Androgen receptors (ARs) are overexpressed in normal tissues and in most primary and metastatic prostate cancers. In our efforts to develop a nonsteroidal AR-specific imaging agent, we synthesized (+/-)-3-[(76)Br]bromo-hydroxyflutamide ((76)Br-), an analog of hydroxyflutamide, the active metabolite of the AR antagonist ligand flutamide. MATERIALS AND METHODS: (76)Br- was synthesized in three steps, starting with commercially available compounds. Labeling of (76)Br- was achieved through the nucleophilic opening of an epoxide intermediate, and a labeled compound was obtained in high specific activity and good radiochemical yield. RESULTS AND DISCUSSION: (+/-)-3-Bromo-hydroxyflutamide has a significantly higher affinity for ARs compared to hydroxyflutamide, its parent compound. The androgen target-tissue uptake of (76)Br- in diethylstilbestrol-treated male rats was examined; however, AR-mediated uptake was minimal due most likely to the rapid metabolic debromination of the radiolabeled ligand. CONCLUSIONS: This study is part of our first look at a novel class of nonsteroidal AR antagonists as positron emission tomography (PET) imaging agents, which are alternatives to steroidal AR agonist-based imaging agents. Although (76)Br- has a significant affinity for ARs, it showed limited promise as a PET imaging agent because of its poor target-tissue distribution properties.

Animals↗

PubMed2006

Toward standardization of cardiac troponin I measurements part II: assessing commutability of candidate reference materials and harmonization of cardiac troponin I assays.

BACKGROUND: Cardiac tropoin I (cTnI) measurements show an approximately 20- to 40-fold difference between assays, and better standardization and harmonization are needed. Toward this goal, the AACC cTnI Standardization Committee collaborated with the National Institute of Standards and Technology (NIST) in an earlier study to select 2 candidate reference materials (cRMs). METHODS: Two troponin cRMs, a troponin C-troponin I-troponin T (CIT) complex from human heart tissue and a CIT complex from recombinant technology, were supplied to NIST for assessment of composition and purity, and cTnI value assignment. These cRMs and 6 cTnI-positive human serum pools were shipped to manufacturers of 15 cTnI assays. Commutability of the materials was examined by determining the numerical relationship for the cRM preparations between each manufacturer-specified field method and each of the other 14 field methods. These relationships were then compared with the corresponding numerical relationships for the human serum pools. Harmonization of methods was accomplished by determining regression parameters relative to the analytical system yielding values closest to the median for each serum pool. These regression parameters were used to recalculate pool values to harmonize the assays. Interassay CVs before and after harmonization were determined. RESULTS: Characterization of the CIT and CI cRMs showed that these materials were of specified composition. The proportion of cTnI methods that demonstrated commutability for the CIT cRM was 45%; for the CI cRM, 39% of methods demonstrated commutability. Interassay cTnI variability for the field methods ranged from 82% to 97%, median 88%. After harmonization, variability of the serum pools for the cTnI methods was decreased to between 9.0% and 23%, median 15.5%. CONCLUSIONS: The proportion of methods demonstrating commutability was too low for use as a common calibrator for the cTnI field methods. However a simple strategy using serum pools can improve harmonization of field cTnI methods by more than 5-fold. The CIT cRM was selected by the AACC cTnI standardization committee, and a new lot has been classified as the cTnI certified reference material Standard Reference Material 2921 by NIST.

Calibration↗

PubMed2006

Development and evaluation of a candidate reference measurement procedure for the determination of 19-norandrosterone in human urine using isotope-dilution liquid chromatography/tandem mass spectrometry.

19-Norandrosterone (19-NA) is the major metabolite of the steroid nandrolone, one of the most commonly abused anabolic androgenic agents. 19-NA exists mainly as the glucuronide form in human urine. A candidate reference measurement procedure for 19-NA in urine involving isotope dilution coupled with liquid chromatography/tandem mass spectrometry (LC/MS/MS) has been developed and critically evaluated. The 19-NA glucuronide was enzymatically hydrolyzed, and the 19-NA along with its internal standard (deuterated 19-NA) was extracted from urine using liquid-liquid extraction prior to reversed-phase LC/MS/MS. The accuracy of the measurement of 19-NA was evaluated by a recovery study of added 19-NA. The recovery of the added 19-NA ranged from 99.1 to 101.4%. This method was applied to the determination of 19-NA in urine samples fortified with 19-NA glucuronide at three different concentrations (equivalent to 1, 2, and 10 ng/mL 19-NA). Excellent reproducibility was obtained with within-set coefficients of variation (CVs) ranging from 0.2 to 1.2%, and between-set CVs ranging from 0.1 to 0.5%. Excellent linearity was also obtained with correlation coefficients of all linear regression lines (measured intensity ratios vs mass ratios) ranging from 0.9997 to 0.9999. The detection limit for 19-NA at a signal-to-noise ratio of approximately 3 was 16 pg. The mean results of 19-NA yielded from hydrolysis of 19-NA glucuronide compared well with the theoretical values (calculated from the conversion of 19-NA glucuronide to 19-NA) with absolute relative differences ranging from 0.2 to 1.4%. This candidate reference measurement procedure for 19-NA in urine, which demonstrates good accuracy and precision and low susceptibility to interferences, can be used to provide an accuracy base to which routine methods for 19-NA can be compared and that will serve as a standard of higher order for measurement traceability.

Chromatography, Liquid↗

PubMed2006

Development of a new standard reference material: SRM 1955 (homocysteine and folate in human serum).

Total homocysteine (tHCY) and folate are interrelated biomarkers for arteriosclerosis and coronary heart disease. Although many different methods for both tHCY and folate are clinically available, the intermethod and interlaboratory results are often poor, resulting in the need for a matrix reference material and reference methods. The National Institute of Standards and Technology (NIST) has developed isotope dilution liquid chromatography/mass spectrometry (LC/MS) and liquid chromatography/ tandem mass spectrometry (LC/MS/MS) methods for determination of tHCY and several folate forms including 5-methyltetrahydrofolic acid (5MT) and folic acid (FA). Additionally, a method for simultaneous measurement of tHCY, 5MT, and FA has been developed and validated. In collaboration with the Centers for Disease Control and Prevention (CDC), mass spectrometric methods and methods used in clinical laboratories have been applied to characterize a new Standard Reference Material (SRM), SRM 1955, "Homocysteine and Folate in Human Serum," containing low, medium, and high levels of tHCY and 5MT. Additionally, FA, 5-formyltetrahydrofolic acid (5FT), vitamin B12, and total folate values are provided. Use of the new SRM should improve clinical measurements and will permit traceability to internationally recognized certified reference materials, as described by European Directive 98/79/EC on in vitro diagnostic medical devices.

Folic Acid↗

PubMed2006

In vivo skeletal imaging of 18F-fluoride with positron emission tomography reveals damage- and time-dependent responses to fatigue loading in the rat ulna.

The skeletal response to damaging fatigue loading is not fully understood. We used (18)F-fluoride PET to describe the time course of the skeletal response following the creation of increasing levels of in vivo, fatigue-induced damage. The right forelimbs of 40 adult rats were loaded in vivo in cyclic compression to four levels of subfracture, fatigue displacement: 30, 45, 65, or 85% of fracture displacement. Rats were injected with a bone-seeking radionuclide ((18)F-fluoride) on days 0 (4 h), 2, 4, 7, 9, 11, 18, 24, and 30, and imaged using a small animal positron emission tomography (PET) scanner. We quantified fluoride uptake in the central 50% of the right (loaded) and left (control) forelimbs. There were significant increases in fluoride uptake in loaded forelimbs compared to control on day 0 for all displacement groups. Normalized uptake (loaded/control) reached peak levels 4 to 9 days after loading. Normalized uptake depended significantly on the level of fatigue displacement. Normalized uptake increased progressively from the 30 to the 45% displacement level (P < 0.001), and from the 45 to the 65% level (P < 0.001) but did not differ between 65 and 85% (P = 0.41). Histologically, we observed a rapid periosteal response with increased vascularity as early as day 1 and abundant woven bone formation between days 3 and 7. Periosteal and woven bone thicknesses were greater in bones subjected to more fatigue displacement. We conclude that a single bout of fatigue loading leads to a transient increase in the uptake of (18)F-fluoride, that the uptake is in proportion to the level of initial damage and is associated with increased vascularity and woven bone formation in the first week after loading.

Animals↗

PubMed2006

New approach to fully automated synthesis of sodium [18F]fluoroacetate -- a simple and fast method using a commercial synthesizer.

A simple, rapid and fully automated preparation of sodium [(18)F]fluoroacetate has been developed by taking advantage of the similarities between the reaction pathways of [(18)F]fluoroacetate and [(18)F]-2-fluoro-deoxyglucose (FDG). The automated synthesis of sodium [(18)F]fluoroacetate was achieved with a commercial [(18)F]FDG synthesizer, the TRACERlab MX(FDG). The method produced the desired compound in a short synthesis time (32 min) and with a high and reproducible radiochemical yield (50.2 +/- 4.8%, decay corrected). The radiochemical purity of sodium [(18)F]fluoroacetate was greater than 99%.

Equipment Design↗

PubMed2006

Three-dimensional maximum a posteriori (MAP) imaging with radiopharmaceuticals labeled with three Cu radionuclides.

BACKGROUND: One of the limiting factors in achieving the best spatial resolution in positron emission tomography (PET), especially in small-animal PET, is the positron range associated with the decay of nuclides, and usual PET image reconstruction algorithms do not provide a correction for the positron range. This work presents initial results obtained with the maximum a posteriori (MAP) algorithm, which has been developed to include an accurate model of the camera response, the Poisson distribution of coincidence data and the fundamental physics of positron decay including the positron range. METHODS: Phantoms were imaged with three positron emitting isotopes of Cu ((60)Cu, (61)Cu and (64)Cu), and mice and rats were imaged with two radiopharmaceuticals labeled with these isotopes in a microPET-R4 camera. These isotopes decay by positron emission with very different end-point energies resulting in wildly different spatial resolutions. Spatial resolution improvement and image quality offered by the MAP algorithm were studied with the line source phantom and a miniature Derenzo phantom. In addition, three mice and three rats were sequentially injected over a 48-h period with Cu-pyruvaldehyde bis(N(4)-methylthiosemicarbazone) (for blood flow to organs) and Cu-1,4,7,10-tetraazacyclododecane-1,4,7-tri(methanephosphonic acid) (for bone imaging) labeled with the said three isotopes of Cu. RESULTS: The line source experiment showed that comparable spatial resolution is possible with all three isotopes when using the positron range correction in MAP. The in vivo images obtained from (60)Cu and (61)Cu and reconstructed with 2D filtered back projection algorithms provided by the camera manufacturer show reduced clarity due to degraded spatial resolution arising from the extended positron ranges as compared with (64)Cu. MAP reconstructions exhibited a higher resolution with clearer organ delineation. CONCLUSION: Inclusion of a positron range model in the MAP reconstruction algorithm may potentially result in significant resolution recovery for isotopes with larger positron ranges.

Algorithms↗

PubMed2006

Automatic synthesis of 16 alpha-[(18)F]fluoro-17beta-estradiol using a cassette-type [(18)F]fluorodeoxyglucose synthesizer.

16 alpha-[(18)F]fluoro-17beta-estradiol ([(18)F]FES) is a radiotracer for imaging estrogen receptors by positron emission tomography. We developed a clinically applicable automatic preparation system for [(18)F]FES by modifying a cassette-type [(18)F]fluorodeoxyglucose synthesizer. Two milligrams of 3-O-methoxymethyl-16,17-O-sulfuryl-16-epiestriol in acetonitrile was heated at 105 degrees C for 10 min with dried [(18)F]fluoride. The resultant solution was evaporated and hydrolyzed with 0.2 N HCl in 90% acetonitrile/water at 95 degrees C for 10 min under pressurized condition. The neutralization was carried out with 2.8% NaHCO(3), and then the high-performance liquid chromatography (HPLC) purification was performed. The desired radioactive fraction was collected and the solvent was replaced by 10 ml of saline, and then passed through a 0.22-microm filter into a pyrogen-free vial as the final product. The HPLC purification data demonstrated that [(18)F]FES was synthesized with a yield of 76.4+/-1.9% (n=5). The yield as the final product for clinical use was 42.4+/-3.2% (n=5, decay corrected). The total preparation time was 88.2+/-6.4 min, including the HPLC purification and the solvent replacement process. The radiochemical purity of the final product was >99%, and the specific activity was more than 111 GBq/micromol. The final product was stable for more than 6 h in saline containing sodium ascorbate. This new preparation system enables us to produce [(18)F]FES safe for clinical use with high and reproducible yield.

Drug Stability↗

PubMed2006

Synthesis and biological evaluation of a fluorine-18-labeled nonsteroidal androgen receptor antagonist, N-(3-[18F]fluoro-4-nitronaphthyl)-cis-5-norbornene-endo-2,3-dicarboxylic imide.

INTRODUCTION: Androgen receptor (AR), which is overexpressed in most prostate cancers, is the target of androgen ablation and antiandrogen therapies: it is also the target for the receptor-mediated imaging of AR-positive prostate cancer using radiolabeled ligands. Previous AR imaging agents were based on a steroidal core labeled with fluorine. To develop a novel class of nonsteroidal imaging agents, with binding and pharmacological characteristics that are more similar to those of clinically used AR antagonists, we synthesized N-(3-fluoro-4-nitronaphthyl)-cis-5-norbornene-endo-2,3-dicarboxylic imide (3-F-NNDI), an analog of recently reported AR antagonist ligands. METHODS: 3-F-NNDI was synthesized in six steps starting with 1-nitronaphthalene, with fluorine incorporation as the final step. The labeling of 3-F-NNDI with fluorine-18 was achieved through a novel, extremely mild, S(N)Ar displacement reaction of an o-nitro-activated arene trimethylammonium salt, and 3-[(18)F]F-NNDI was prepared in high specific activity. RESULTS AND DISCUSSION: 3-F-NNDI was found to have an AR-binding affinity similar to that of its parent compound. In vitro assays demonstrated high stability of the labeled compound under physiological conditions in buffer and in the blood. Androgen target tissue uptake in diethylstilbestrol-pretreated male rats, however, was minimal, probably because of extensive metabolic defluorination the radiolabeled ligand. CONCLUSIONS: This study is part of our first look at a novel class of nonsteroidal AR antagonists as positron emission tomography (PET) imaging agents that are alternatives to steroidal AR agonist-based imaging agents. Although 3-[(18)F]F-NNDI has significant affinity for AR, it showed limited promise as a PET imaging agent because of its poor target tissue distribution properties.

Animals↗

PubMed2006

Advances in the production, processing and microPET image quality of technetium-94m.

This work involves the production, processing and imaging of the short-lived, rarely used positron emission tomography (PET) radionuclide technetium-94m (94mTc). Our procedures are an extension of methods reported in the literature and are detailed within. A key modification was the development of a single step that combines purification and concentration of an aqueous 94mTc-pertechnetate solution, which both reduces processing time and increases the final concentration of the solution. Additionally, a convenient method for the direct recovery of 94mTc into an organic solvent was developed, eliminating the solvent transfer step needed for organic syntheses using 94mTc. Each of these advances potentially extends the scope of syntheses possible with this short-lived radionuclide. To explore the imaging potential of 94mTc, we carried out phantom imaging studies on small-scale high-resolution PET scanners to estimate the limitations of detection associated with 94mTc and PET. Preliminary studies demonstrate that useful images can be obtained with modern image reconstruction algorithms when using a correction for the cascade gamma ray contamination.

Isotope Labeling↗

PubMed2006

Synthesis and evaluation of a bromine-76-labeled PPARgamma antagonist 2-bromo-5-nitro-N-phenylbenzamide.

Peroxisome proliferator activated-receptor gamma (PPARgamma) binds to peroxisome receptor response elements with its heterodimeric partner, retinoid X receptor, and regulates downstream gene expression. PPARgamma transcriptionally modulates fat metabolism, and receptor agonists have been developed to treat type II diabetes. PPARgamma is also overexpressed in some tumor cell lines and primary tumors, including breast and prostate tumors. Two PPARgamma antagonists, 2-chloro-5-nitro-N-phenylbenzamide (GW9662) and 2-chloro-5-nitro-N-pyridin-4-yl-benzamide (T0070907), represent good lead compounds for radiotracer development. In the current study, four additional halogen substituted analogs were synthesized and evaluated in a whole cell screening assay for PPARgamma binding activity. Two bromine-containing analogs having EC50 values <5 nM were chosen for bromine-76 radiolabeling. Bromine-76-labeled 2-bromo-5-nitro-N-phenyl-benzamide was selected for subsequent in vitro and in vivo studies due to its superior radiolabeling yield (approximately 70%) and the well-characterized pharmacological properties of its analog GW9662. An in vitro stability study showed that 40% of the compound remained intact in plasma and about 25% in whole blood after 30 min. Biodistribution studies in MDA-MB-435 human breast tumor-bearing nude mice were carried out at 5 min, 30 min, 2 h and 24 h post injection of the radiotracer. Although in vivo metabolite studies demonstrated rapid compound degradation, at least 10% of the parent compound was delivered to the tumor. We are currently exploring second generation analogs of these lead compounds for the development of radiolabeled antagonists of the PPARgamma receptor.

Anilides↗

PubMed2006

Monitoring the effect of mild hyperthermia on tumour hypoxia by Cu-ATSM PET scanning.

PURPOSE: Mild hyperthermia can improve tumour oxygenation and enhance radiosensitivity. Imaging the hypoxic fraction of a tumour can guide hyperthermia treatment planning and facilitate treatment optimization. 64Cu-ATSM (Copper-diacetyl-bis(N4-methylthiosemicarbazone)) is a positron emitting compound that has been demonstrated to have rapid uptake and selective retention in hypoxic cells and has been used for imaging human and animal tumours. The purpose of the present report is to establish methodology that will allow one to use Cu-ATSM PET scanning to detect the impact of hyperthermia on tumour physiology in as little time as possible. MATERIALS AND METHODS: EMT6 tumours (mouse mammary carcinoma) were implanted into the subcutaneous tissue of both thighs of 10 BALB/c mice (one heated, one control tumour per animal). The target thermal dose was 41.5 degrees C x 45 min. Without interrupting heating, 64Cu-ATSM (mean activity 1.8 mCi) was then injected and serial PET scans were obtained. In a sub-group of four animals, a low administered activity (approximately 0.3 mCi) 64Cu-ATSM scan was also conducted before heating to permit a direct comparison of the effects of hyperthermia on the same tumours. In another sub-group of five animals, a low activity (approximately 0.3 mCi) 64Cu-PTSM (pyruvaldehyde-bis(N*-methylthiosemicarbazone)) scan was conducted before heating, to confirm a posited correlation between perfusion and early 64Cu-ATSM uptake. RESULTS: This study corrected for perfusion differences by dividing tumour uptake by the average early (first minute) uptake ('self-normalized uptake'). The 10 heated tumours showed a significantly (p = 0.007) lower self-normalized uptake than control tumours by 2 min. For the four mice with low activity Cu-ATSM scans performed before hyperthermia, the tumours to be heated demonstrated self-normalized uptake consistent with the unheated control tumours and which departed significantly (p < or = 0.02) from their post-hyperthermia scans by 5 min. Comparisons between scans and needle electrode surveys were performed in an additional four animals with eight tumours. For technical reasons electrode surveys were done after the end of hyperthermia-and, therefore, these animals also had comparison scans taken after hyperthermia. Reduced self-normalized uptake on scans was associated with increased pO2 on electrode surveys. These data also suggested a substantial degradation of the effect on tumour hypoxia by approximately 15-45 min after the end of mild hyperthermia. CONCLUSION: Short imaging times of approximately 5 min with modest (approximately 4-10) numbers of mice can discriminate the effects of mild hyperthermia on tumour physiology. The long-term objective is to use this tool to identify as short and mild a hyperthermia session as possible.

Animals↗

PubMed2006

Minimally invasive method of determining blood input function from PET images in rodents.

UNLABELLED: For cardiovascular research on rodents, small-animal PET has limitations because of the inherent spatial resolution of the system and because of cardiac motion. A factor analysis (FA) technique for extracting the blood input function and myocardial time-activity curve from dynamic small-animal PET images of the rodent heart has been implemented to overcome these limitations. METHODS: Six Sprague-Dawley rats and 6 BALB/c mice underwent dynamic imaging with 18F-FDG (n = 6) and 1-11C-acetate (n = 6). From the dynamic images, blood input functions and myocardial time-activity curves were extracted by the FA method. The accuracy of input functions derived by the FA method was compared with that of input functions determined from serial blood samples, and the correlation coefficients were calculated. RESULTS: Factor images (right ventricle, left ventricle, and myocardium) were successfully extracted for both 18F-FDG and 1-11C-acetate in rats. The correlation coefficients for the input functions were 0.973 for 18F-FDG and 0.965 for 1-11C-acetate. In mice, the correlation coefficients for the input functions were 0.930 for 18F-FDG and 0.972 for 1-11C-acetate. CONCLUSION: The FA method enables minimally invasive extraction of accurate input functions and myocardial time-activity curves from dynamic microPET images of rodents without the need to draw regions of interest and without the possible complications of surgery and repeated blood sampling.

Animals↗

PubMed2006

Assessment of myocardial blood flow using 15O-water and 1-11C-acetate in rats with small-animal PET.

UNLABELLED: This feasibility study was undertaken to determine whether myocardial blood flow (MBF, mL/g/min) could be quantified noninvasively in small rodents using microPET and 15O-water or 1-11C-acetate. METHODS: MBF was measured in 18 healthy rats using PET and 15O-water (MBF-W) under different interventions and compared with direct measurements obtained with microspheres (MBF-M). Subsequently, MBF was estimated in 24 rats at rest using 1-11C-acetate (MBF-Ace) and compared with measurements obtained with 15O-water. Using factor analysis, images were processed to obtain 1 blood and 1 myocardial time-activity curve per tracer per study. MBF-W was calculated using a well-validated 1-compartment kinetic model. MBF-Ace was estimated using a simple 1-compartment model to estimate net tracer uptake, K1 (K1 (mL/g/min) = MBF.E; E = first-pass myocardial extraction of 1-11C-acetate) and washout (k2 (min(-1))) along with F(BM) (spillover correction) after fixing F(MM) (partial-volume correction) to values obtained from 15O-water modeling. K1 values were converted to MBF values using a first-pass myocardial extraction/flow relationship measured in rats (E = 1.0-0.74.exp(-1.13/MBF)). RESULTS: In the first study, MBF-W correlated well with MBF-M (y = 0.74x + 0.96; n = 18, r = 0.91, P < 0.0001). However, the slope was different than unity, P < 0.05). Refitting of the data after forcing the intercept to be zero resulted in a nonbias correlation between MBF-W and MBF-M (y = 0.95x + 0.0; n = 18, r = 0.86, P < 0.0001) demonstrating that the underestimation of the slope could be attributed to the overestimation of MBF-W for 2 MBF-M values lower than 1.50 mL/g/min. In the second study, MBF-Ace values correlated well with MBF-W with no underestimation of MBF (y = 0.91x + 0.35; n = 24, r = 0.87, P < 0.0001). CONCLUSION: MBF can be quantified by PET using (15)O-water or 1-11C-acetate in healthy rats. Future studies are needed to determine the accuracy of the methods in low-flow states and to develop an approach for a partial-volume correction when 1-11C-acetate is used.

Acetates↗