Predictions of Gibbs free energies for the adsorption of polyaromatic and nitroaromatic environmental contaminants on carbonaceous materials: efficient computational approach

The adsorption of benzene, polycyclic aromatic hydrocarbons (PAHs), and nitroaromatic compounds (NACs) on the carbonaceous surfaces from the gas phase and water solution was investigated. Several different levels of theory were applied, including DFT-, MP2-, and CCSD(T)-based methods, to find an approach that is computationally inexpensive and can provide accurate thermodynamic parameters for studied adsorption phenomena. The methods and techniques used (including cluster and periodic approximations) were evaluated on the basis of comparison with available experimental data. The optimized structures of calculated complexes are obtained, and the interaction energies and Gibbs free energies are predicted. Good agreement was revealed for the theoretical and experimental adsorption energies of benzene and PAHs adsorbed on the carbon surfaces. The adsorption of benzene, PAHs, and NACs on carbon is suggested to be effective from the gas phase for all studied compounds and for PAHs and NACs also from water solution at room temperature.

Recombinant NY‐ESO‐1 Cancer Antigen: Production and Purification under cGMP Conditions

The cancer-testis antigen, NY-ESO-1, has been engineered into a bacterial expression plasmid which incorporates a His6-tag. The plasmid was transfected into E. coli strain BL21 and Master and Working cell banks generated from this expression system. Three 15-litre fermentations were performed under cGMP (code of Good Manufacturing Practice) conditions and the crude NY-ESO-1 tagged protein isolated as solubilised inclusion bodies. A three-step cGMP chromatography process (immobilised metal affinity, anion exchange, and hydrophobic interaction) was utilised to purify the protein. The purified NY-ESO-1 is being used in early stage human cancer vaccine trials in Australia and the U.S.A.

Synthesis of 17,20beta,21-trihydroxypregn-4-en-3-one by ovaries of reproductively mature Atlantic cod Gadus morhua

Atlantic cod Gadus morhua ovaries were incubated in vitro with tritiated 17-hydroxypregn-4-ene-3,20-dione (17-P) to determine whether 17,20beta-dihydroxypregn-4-en-3-one (17,20beta-P) or 17,20beta, 21-trihydroxypregn-4-en-3-one (17,20beta,21-P), or both, were more likely to be the steroid responsible for inducing oocyte final maturation (i.e. resumption of meiosis). Only 17,20beta,21-P was produced, in addition to 11-deoxycortisol (17,21-P), which is intermediate between 17-P and 17,20beta,21-P. Also, the 5beta-reduced forms of 17-P, 17,21-P and 17,20beta,21-P were all found. Some sulphation of 21-hydroxylated steroids was demonstrated. The ability of female G. morhua to make 17,20beta,21-P but not 17,20beta-P was confirmed by radioimmunoassay of plasma samples from spawning fish. Although small amounts of 17,20beta-P immunoreactivity were detected in a few plasma samples, this was shown, by thin-layer chromatography, to be mostly due to cross-reaction with other unidentified compounds. The evidence strongly suggests that 17,20beta,21-P is more likely than 17,20beta-P to be the maturation-inducing steroid in G. morhua.

The efficacy of Artecoll injections for the augmentation of nipple projection in breast reconstruction

INTRODUCTION

Various techniques have been used in an attempt to achieve long-term nipple projection following nipple-areolar reconstruction. A common setback, however, is the diminution of projection overtime; this phenomenon is particularly evident following implant-based breast reconstruction. Artecoll may be suitable for injection into the nipple complex to maintain permanent, 3-dimensional projection. Artecoll is an injectable substance that is biocompatible and immunologically inert and resists degradation in vivo. The purpose of this study was thus to prospectively evaluate the efficacy of Artecoll (polymethylmethacrylate microspheres suspended in 3.5% denatured bovine collagen with 0.3% lidocaine) in obtaining and maintaining nipple projection following postmastectomy, nipple-areolar reconstruction.

METHODS

A prospective, clinical trial was performed. Consecutive patients deemed to have inadequate nipple projection at least 6 months following "C-V flap" or "modified-skate flap" reconstruction were identified. Only women who had postmastectomy reconstruction with tissue expanders and implants were considered eligible for participation. Artecoll was injected under the nipple at 2 time points: baseline and 3 months. Calipers were used to measure nipple projection preinjection and postinjection at baseline, 3, 6, and 9 months.

RESULTS

Thirty-three nipples were injected in 23 patients. There were no adverse events. Prior to injection, mean nipple projection was 1.33 +/- 1.0 mm. The mean increase in projection over the 9-month study period was both clinically and statistically significant (1.60 +/- 1.24 mm; P <.001). A history of prior irradiation was a significant negative predictor of final nipple projection (P = .012).

CONCLUSION

Artecoll injection is both feasible and effective in increasing and maintaining nipple projection in the setting of implant-based breast reconstruction.

Isoelectric focusing of horse serum esterase isozymes and detection of new phenotypes

A new method for separating the isozymes of horse serum esterase is described. The improved resolution has enabled us to detect several previously undescribed phenotypes. This method has also been used to detect two different apparently 'silent' alleles.

Novel alpha haemoglobin haplotypes in horses

Four minor haplotypes that produce abnormal haemoglobin phenotypes in horses have been characterized. Two of them, AIIb and V, are copy number variants with, respectively, one and three alpha genes instead of the normal complement of two. The AIIa and C haplotypes, on the other hand, each have two alpha genes but, as a result of probable gene conversions, they now encode identical, though haplotype specific, globins. Two out of 60 unrelated and phenotypically normal horses studied had an unusual triplicated rearrangement in the embryonic zeta-gene locus. Each of these variants appears to have been produced by aberrant recombination events.

Positron emission tomography changes management and prognostic stratification in patients with oesophageal cancer: results of a multicentre prospective study

OBJECTIVES

The aims of this study were (1) to determine the incremental information provided by (18)F-FDG positron emission tomography (PET) in staging patients with oesophageal cancer, and (2) to determine the impact of PET staging on post-PET clinical management of oesophageal cancer, and on prognosis.

METHODS

In a multicentre, single-arm open study, patients with proved oesophageal cancer without definite distant metastases and regarded as suitable for potentially curative treatment were examined by PET. Clinicians were requested to supply a management plan before and another plan after being supplied with the PET scan results. Patients were followed for at least 1 year for outcome analysis.

RESULTS

A total of 129 patients (104 men, mean age 67 y) were recruited. PET detected additional sites of disease in 53 patients (41%). Significant changes in management (high or medium impact) were observed in 38% of patients, primarily as a result of identifying additional sites of disease and/or confirming previously equivocal regional and distant metastases. Progression-free survival was significantly shorter in patients found to have additional lesions on PET (p < 0.05), but was not related to SUV(max).

CONCLUSION

These findings demonstrate the significant impact of PET on the clinical management of patients with newly diagnosed oesophageal carcinoma, and on prognostic stratification of these patients.

Role of low-dose, noncontrast computed tomography from integrated positron emission tomography/computed tomography in evaluating incidental 2-deoxy-2-[F-18]fluoro-D-glucose-avid colon lesions

PURPOSE

To assess the contribution of concurrent low-dose, noncontrast CT in the assessment of the malignant potential of incidental focal 2-deoxy-2-[F-18]fluoro-D-glucose (FDG)-avid colonic lesions on positron emission tomography/computed tomography (PET/CT).

PROCEDURES

Routine FDG-PET/CT scans were reviewed for identification of focal FDG-avid colon lesions, and the CT component was independently reviewed for an anatomical lesion and malignant potential based on CT criteria. Clinical, endoscopic, and histopathology follow-up was obtained.

RESULTS

A total of 85/2,916 (3%) oncology FDG-PET/CT scans had incidental focal colon lesions. Clinical and/or endoscopic follow-up was available in 83/85 (98%) patients. Focal, corresponding CT lesions were found in 44/83 (53%) patients, but features of malignancy were not assessable. Of the 44 patients with a final diagnosis, 32/44 (73%) were FDG-PET/CT true positives; 5/44 (11%) were false positives; and 7/44 (16%) had inconclusive FDG-PET/CT findings.

CONCLUSIONS

Concurrent low-dose, noncontrast CT improves localization, but does not provide independent information on the malignant potential of incidental focal colonic activity on FDG-PET/CT.

The expanding role of PET technology in the management of patients with colorectal cancer

The therapeutic options and subsequent survival of colorectal cancer (CRC) patients has increased substantially over recent years. While surgical excision of the primary cancer results in cure of approximately 50% of patients, recurrence and metastatic disease still remains a significant cause of death. Although resection of liver or lung metastases can result in cure, relapse rates remain high, indicating that patient selection needs improvement. Positron emission tomography (PET) technology has a great deal to offer with respect to CRC management, particularly in the setting of patient selection for metastasectomy and in the evaluation of possible recurrent disease, however it has not yet become a routine part of the management of all CRC patients. This review article aims to discuss the current and future implications of PET technology in the optimal management of CRC patients throughout their care pathway.

Prevalence of occult metastatic disease in patients undergoing 18F-FDG PET for primary diagnosis or staging of lung carcinoma and solitary pulmonary nodules

BACKGROUND

Accurate staging of lung cancer is essential in determining the most appropriate management plan, as detection of occult metastasis can significantly alter management.

AIMS

The aims of this study are to determine the prevalence of occult metastasis in patients undergoing 2-(18)F-fluoro-2-deoxy-D-glucose ((18)F-FDG) positron emission tomography (PET) for evaluation of suspected/proven lung carcinoma and correlate pre-PET TNM stage with prevalence of metastasis.

METHODS

FDG-PET, which identified patients with metastasis on institutional database, was re-evaluated by a nuclear medicine physician blinded to clinical information. The confidence level of metastasis was scored on a 5-point scale, with a score of >/=4 considered positive.

RESULTS

There were 67 of 645 (10%) patients identified with suspected occult metastasis on FDG-PET. Twelve patients scoring </=3 were excluded. Prevalence of occult metastasis was 10/156 (6%) in solitary pulmonary nodules (SPN); 22/319 (7%) and 23/170 (14%) in proven and suspected lung cancer, respectively. Positive predictive value of FDG-PET for metastasis was 8/10 (80%) in solitary pulmonary nodules, 14/20 (70%) and 17/21 (81%) in proven and suspected lung cancer, respectively. (18)F-FDG-avid lesions classified as false positives were patients with cholelithiasis, rib fractures and those with equivocal/negative bone scans or computed tomography on follow up. There was a higher incidence of true positive occult metastasis in patients in all stages of disease, particularly stage III disease.

CONCLUSION

(18)F-FDG PET is predictive for occult metastatic disease in patients with solitary pulmonary nodules and proven or suspected lung cancer and is more likely to be present in all stages, particularly in stage III. PET findings should be actively pursued with correlative investigation to identify benign pathology in patients who remain candidates for curative treatment.

Phase stabilization of a large-mode-area ytterbium-doped fiber amplifier

Measurements are reported on the open and closed-loop phase stability of a large-mode-area ytterbium-doped fiber amplifier. Phase fluctuations are characterized by a high-frequency low-amplitude jitter superimposed on a slow power-dependent drift. The amplifier may be phase locked to a precision of lambda/20 by using a low-bandwidth feedback loop.

Fluorine-18 fluorothymidine: a new positron emission radioisotope for renal tumors

Fluorine-18 fluorothymidine (F-18 FLT) is a radioisotope based on the nucleic acid thymidine and has emerged as an important tracer that mirrors cellular proliferation in positron emission tomography (PET) studies. Early studies in human tumors have been promising. However, imaging of renal tumors using F-18 FLT PET studies has not previously been described. In this report, a difficult case of renal transitional cell carcinoma in a longstanding cyst was clearly delineated using F-18 FLT. Importantly, the study was able to guide clinicians toward appropriate surgical management. The use of such tracers may herald a new era in renal tumor imaging.

Anterior cingulate activation in antipsychotic-naïve first-episode schizophrenia

Anterior cingulate (ACC) hypo-activity is commonly observed in chronically ill schizophrenia patients. However, it is unclear whether this is secondary to persistent illness and/or medication.

METHOD

We examined eight antipsychotic-naïve first-episode patients and matched healthy controls undergoing PET scanning while performing the Stroop task.

RESULTS

Group-averaged and single-subject analyses showed ACC activation in both controls and patients, albeit in different sub-regions (paracingulate and cingulate respectively). A direct comparison revealed relative under-activity of the left paracingulate cortex in patients.

CONCLUSION

These findings suggest that the more pervasive hypo-activation observed in chronic patients may be secondary to persistent illness and/or medication.

The inflammatory caspases: guardians against infections and sepsis

Innate immunity is the primary host defense against invading microorganisms. Pathogen recognition, mediated through an elaborate 'microbial sensing' system comprising the Toll-like and Nod-like receptor families results in the activation of caspase-1, which is a prerequisite for pathogen clearance. Tight regulation of caspase-1 is necessary to control the magnitude of the innate immune response and protect the organism from possible damaging effects such as sepsis. Recent findings from population studies and animal models of infectious diseases and sepsis have uncovered a role for full-length caspase-12 in blocking the inflammatory response initiated by caspase-1, thus predisposing the organism to severe sepsis and sepsis-related lethality. In this review, we re-examine the relationship among the Group I caspases, their known substrates and their proposed role in apoptosis. We further discuss their function in inflammation and bacterial clearance, with an emphasis on their regulatory mechanisms during the innate immune response.

Somatostatin receptor expression, tumour response, and quality of life in patients with advanced hepatocellular carcinoma treated with long-acting octreotide

Octreotide may extend survival in hepatocellular carcinoma (HCC). Forty-one per cent of HCCs have high-affinity somatostatin receptors. We aimed to determine the feasibility, safety, and activity of long-acting octreotide in advanced HCC; to identify the best method for assessing somatostatin receptor expression; to relate receptor expression to clinical outcomes; and to evaluate toxicity. Sixty-three patients with advanced HCC received intramuscular long-acting octreotide 20 mg monthly until progression or toxicity. Median age was 67 years (range 28–81 years), male 81%, Child–Pugh A 83%, and B 17%. The aetiologies of chronic liver disease were alcohol (22%), viral hepatitis (44%), and haemochromatosis (6%). Prior treatments for HCC included surgery (8%), chemotherapy (2%), local ablation (11%), and chemoembolisation (6%). One patient had an objective partial tumour response (2%, 95% CI 0–9%). Serum alpha-fetoprotein levels decreased more than 50% in four (6%). Median survival was 8 months. Thirty four of 61 patients (56%) had receptor expression detected by scintigraphy; no clear relationship with clinical outcomes was identified. There were few grade 3 or 4 toxicities: hyperglycaemia (8%), hypoglycaemia (2%), diarrhoea (5%), and anorexia (2%). Patients reported improvements in some symptoms, but no major changes in quality of life were detected. Long-acting octreotide is safe in advanced HCC. We found little evidence of anticancer activity. A definitive randomised trial would identify whether patients benefit from this treatment in other ways.

Preclinical analysis of the analinoquinazoline AG1478, a specific small molecule inhibitor of EGF receptor tyrosine kinase

The tyrphostin 4-(3-chloroanilino)-6,7-dimethoxyquinazoline (AG1478) is a potent and specific inhibitor of EGFR tyrosine kinase whose favourable preclinical profile supports progression towards clinical trials. Microphysiometric evaluation revealed a short (<24 min) effective inhibition of cellular receptor response to EGF challenge in BaF/ERX cells indicating a need to maintain sustained levels of inhibitor. Initial pharmacokinetic evaluation in mice of novel AG1478 formulations in a beta-cyclodextrin (Captisol) showed monoexponential elimination from plasma (half-life 30 min) following subcutaneous administration. A two-fold dose escalation gave a 2.4-fold increase in the total AUC. Bolus i.v. and 6 h continuous infusion were investigated in rats to mimic a more clinically relevant administration regimen. Drug elimination following bolus i.v. administration was biphasic (terminal elimination half-life 30-48 min). The linear relationship between dose and AUC(0-->infinity) (r2=0.979) enabled the prediction of infusion rates and doses for sustained delivery using continuous 6 h infusions, where steady state was reached in 120 min. Plasma levels of AG1478>10 microM were achieved over the duration of the infusion. At the lowest dose, plasma drug levels after the cessation of infusion declined with a half-life of approximately 43 min. EGFR activity, measured both by autophosphorylation and downstream signalling, was inhibited in a dose-dependent manner by injection of AG1478 in mice bearing xenografts of the human glioblastoma cell line U87MG.delta2-7, which expresses a constitutively active variant of the EGF receptor. Taken together, these experiments provide essential data to assess the anti-tumour efficacy of AG1478 and will assist in the rational design of dose regimens for clinical studies.

High-power Yb-doped multicore ribbon fiber laser

A highly elongated double-clad ribbon fiber that comprises a pure-silica inner cladding with transverse dimensions of approximately 1.4 mm by 0.23 mm with a linear array of ten ytterbium-doped cores has been fabricated and operated in a simple laser configuration pumped by two diode stacks. The fiber laser yielded 320 W of output power at a center wavelength of 1045 nm in a combined beam with beam propagation factors of approximately 2 (perpendicular to the array) and approximately 150 (parallel to the array) for 576 W of launched pump power. The slope efficiency with respect to absorbed pump power was 62%. The prospects for further power scaling and improved beam quality and efficiency are discussed.

Engineering and characterisation of chimeric monoclonal antibody 806 (ch806) for targeted immunotherapy of tumours expressing de2-7 EGFR or amplified EGFR

We report the generation of a chimeric monoclonal antibody (ch806) with specificity for an epitope on the epidermal growth factor receptor (EGFR) that is different from that targeted by all other anti-EGFR therapies. Ch806 antibody is reactive to both de2-7 and overexpressed wild-type (wt) EGFR but not native EGFR expressed in normal tissues at physiological levels. Ch806 was stably expressed in CHO (DHFR −/−) cells and purified for subsequent characterisation and validated for use in preliminary immunotherapy investigations. Ch806 retained the antigen binding specificity and affinity of the murine parental antibody. Furthermore, ch806 displayed enhanced antibody-dependent cellular cytotoxicity against target cells expressing the 806 antigen in the presence of human effector cells. Ch806 was successfully radiolabelled with both iodine-125 and indium-111 without loss of antigen binding affinity or specificity. The radioimmunoconjugates were stable in the presence of human serum at 37°C for up to 9 days and displayed a terminal half-life (T_1/2β) of approximately 78 h in nude mice. Biodistribution studies undertaken in BALB/c nude mice bearing de2-7 EGFR-expressing or amplified EGFR-expressing xenografts revealed that ¹²⁵I-labelled ch806 failed to display any significant tumour retention. However, specific and prolonged tumour localisation of' ¹¹¹In-labelled ch806 was demonstrated with uptake of 31%ID g⁻¹ and a tumour to blood ratio of 5 : 1 observed at 7 days postinjection. In vivo therapy studies with ch806 demonstrated significant antitumour effects on established de2-7 EGFR xenografts in BALB/c nude mice compared to control, and both murine 806 and the anti-EGFR 528 antibodies. These results support a potential therapeutic role of ch806 in the treatment of suitable EGFR-expressing tumours, and warrants further investigation of the potential of ch806 as a therapeutic agent.

18F-fluorodeoxyglucose positron emission tomography in evaluation of germ cell tumor after chemotherapy

OBJECTIVES

To evaluate the role of 18F-fluorodeoxyglucose (18F-FDG) positron emission tomography (PET) in the assessment of germ cell tumors after chemotherapy.

METHODS

We reviewed patients' records for the histologic findings and clinical outcome. 18F-FDG PET results were correlated with tissue histologic features where available; and if not available, the correlation was with the clinical outcome.

RESULTS

A total of 45 PET studies were performed on 38 patients (age range 19 to 64 years, median 31). All patients had received chemotherapy. In the nonseminomatous germ cell tumor (NSGCT) group, of the 31 patients with one scan, 18 PET scans were reported as positive, with only 2 not having active disease. Of the 12 negative scans, 6 showed teratoma, 1 tumor, and 5 did not show active disease. The equivocal scan revealed thyroid adenoma. In the seminoma group, the PET scans correlated well with the clinical and histologic outcomes. Four patients underwent salvage chemotherapy, and in this subgroup, the PET findings also correlated with the outcome.

CONCLUSIONS

(18)F-FDG PET is a promising tool as an adjunct to current imaging techniques in detecting residual viable germ cell tumor after chemotherapy. In NSGCT, a positive PET scan was accurate in 16 of 18 patients, although negative PET studies did not exclude the presence of disease, mainly because of the presence of teratoma. In seminoma, a negative 18F-FDG PET study correlated with a favorable clinical outcome. PET was also predictive of the response to salvage chemotherapy and was highly specific for active tumor in both NSGCT and seminoma.

Synthesis and evaluation of a thymidine analog for positron emission tomography study of tumor DNA proliferation in vivo

This study describes the synthesis, radiolabelling and biological evaluation of 5-(2,4-difluoro-5-[18F]fluoromethyl-phenyl)-2-hydroxymethyl-tetrahydrofuran-3-ol, 13. Radiolabelling was achieved by reaction of the tosylate 3 with K[18F] in the presence of Kryptofix 222. Good stability in saline and serum solutions at physiological temperatures in vitro was observed. A cell incorporation study of 13 using SW1222 tumor cells showed a linear uptake, unfortunately, in vivo studies indicated that 13 was undergoing defluorination. Rapid defluorination of the radiotracer was confirmed by an in vitro stability study in blood plasma. Finally, a comparison between the DNA uptake of 13 and tritiated thymidine was performed in vitro to asses the potential utility of more stable analogs. These studies showed that 13 and its analogs are unsuitable as potential tracers to image DNA proliferation and highlighted the difficulty in predicting the in vivo stability of novel radiotracers.

Positron emission tomography scanning in the assessment of patients with lymphoma

BACKGROUND

The detection of lymphoma by computed tomography (CT) scanning is known to be improved by positron emission tomography (PET) and/or gallium scanning, although the direct comparative accuracy of these imaging modalities remains a subject of ongoing review.

AIMS

The aim of the present study was to compare PET scanning with conventional imaging (CT and/or gallium scanning) in patients with lymphoma.

METHODS

A retrospective study of 38 patients (25 men; 13 women; median age 39.5 years; range 18.0-81.0 years) who had had PET scans (24 scans at initial staging and 46 scans at restaging, including suspected disease relapse) was carried out. Thirty-one concurrent gallium scans had been performed. Disease was validated with clinical follow up or biopsy.

RESULTS

The sensitivities of PET and CT at initial staging were 96 and 71%, respectively. PET identified additional sites of disease compared with CT in 29% of patients. Of the 15 patients who had had all three imaging modalities, the sensitivities of PET, CT and gallium were 93, 67 and 87%, respectively. At treatment completion, the positive predictive values of PET, CT and gallium scans for relapse given a residual mass were 100, 33 and 0%, respectively (P = 0.006 for PET and CT comparison). The negative predictive values of PET, CT and gallium were 76, 0 and 70%, respectively (P-value not significant). In suspected disease relapse, PET results changed management in 50% of patients.

CONCLUSION

Compared with CT and gallium scans, PET has superior accuracy in staging and restaging, and its greatest value lies in its positive predictive value for relapse in patients with residual masses.

Population pharmacokinetics of sibrotuzumab, a novel therapeutic monoclonal antibody, in cancer patients

Population pharmacokinetics of sibrotuzumab, a humanized monoclonal antibody directed against fibroblast activation protein, were determined after multiple intravenous infusions of dosages ranging from 5 mg/m(2) to an absolute dose of 100 mg, in patients with advanced or metastatic carcinoma. In total, 1844 serum concentrations from 60 patients in three Phase I and II clinical studies were analyzed. The structural model incorporated two disposition compartments and two parallel elimination pathways from the central compartment, one linear and one nonlinear. Finally estimated pharmacokinetic parameters (%RSE) were: linear clearance CLL 22.1 ml/h (9.6), central distribution volume V1 4.13l (3.7), peripheral volume V2 3.19l (8.8), inter-compartmental clearance Q 37.6 ml/h (9.6); for the nonlinear clearance Vmax was 0.0338 mg/h (25) and Km 0.219 microg/ml (57). At serum concentrations between approximately 20 ng/ml and 7 microg/ml, the effect of the nonlinear clearance on pharmacokinetics was marked. Only at >7 microg/ml did CLL dominate overall clearance. Interindividual variability was 57% for CLL, 20% for V1 and V2, and 29% for Vmax and was larger than the inter-occasional variability of 13%. Of the many investigated patient covariates, only body weight was found to contribute to the population model. It significantly affected CLL, V1, V2 and Vmax resulting in marked differences in the model-predicted concentration-time profiles after multiple dosing in patients with low and high body weights. In conclusion, a robust population pharmacokinetic model was developed and evaluated for sibrotuzumab, which identified a possible need to consider body weight when designing dosage regimen for future clinical cancer trials.

Statistical parametric mapping of hypoxic tissue identified by [(18)F]fluoromisonidazole and positron emission tomography following acute ischemic stroke

Positron emission tomography (PET) and the ligand [(18)F]fluoromisonidazole ((18)F-FMISO) have been used to image hypoxic tissue in the brain following acute stroke. Existing region of interest (ROI)-based methods of analysis are time consuming and operator-dependent. We describe and validate a method of statistical parametric mapping to identify regions of increased (18)F-FMISO uptake. The (18)F-FMISO PET images were transformed into a standardized coordinate space and intensity normalized. Then t statistic maps were created using a pooled estimate of variance. Statistical inference was based on the theory of Gaussian Random Fields. We examined the homogeneity of variance in normal subjects and the influence of normalization by mean whole brain activity versus mean activity in the contralateral hemisphere. Validity of the distributional assumptions inherent in parametric analysis was tested by comparison with a non-parametric method. The results of parametric analysis were also compared with those obtained with the existing ROI-based method. Variance in uptake at each voxel in normal subjects was homogeneous and not affected by mean voxel activity or distance from the centre of the image. The method of normalization influenced results significantly. Normalization by whole brain mean activity resulted in a smaller volume of tissue being classified as hypoxic compared to normalisation by mean activity in the contralateral hemisphere. The ROI-based method was subject to interobserver variability with a coefficient of variability of 16%. The volumes of hypoxic tissue identified by parametric and nonparametric methods were highly correlated (r = 0.99). These findings suggest that using a pooled variance and contralateral hemisphere normalisation, statistical parametric mapping can be used to objectively identify regions of increased (18)F-FMISO uptake following acute stroke in individual subjects.