Colonoscopic miss rates of adenomas determined by back-to-back colonoscopies

BACKGROUND & AIMS

The miss rate of colonoscopy for neoplasms is poorly understood. The aim of this study was to determine the miss rate of colonoscopy by same day back-to-back colonoscopy.

METHODS

Two consecutive same day colonoscopies were performed in 183 patients. The patients were randomized to undergo the second colonoscopy by the same or a different endoscopist and in the same or different position.

RESULTS

The overall miss rate for adenomas was 24%, 27% for adenomas < or = 5 mm, 13% for adenomas 6-9 mm, and 6% for adenomas > or = 1 cm. Patients with two or more adenomas at the first examination were more likely than patients with no or one adenoma detected at the first examination to have one or more adenomas at the second examination (odds ratio, 3.3; 95% confidence interval, 1.69-6.46). Right colon adenomas were missed more often (27%) than left colon adenomas (21%), but the difference was not significant. There was evidence of variation in sensitivity between endoscopists, but significant miss rates for small adenomas were found among essentially all endoscopists.

CONCLUSIONS

Using current colonoscopic technology, there are significant miss rates for adenomas < 1 cm even with meticulous colonoscopy. Miss rates are low for adenomas > or = 1 cm. The results suggest the need for improvements in colonoscopic technology.

Efficient production of high specific activity 64Cu using a biomedical cyclotron

Copper-64 (T 1/2 = 12.7 h) is an intermediate-lived positron-emitting radionuclide that is a useful radiotracer for positron emission tomography (PET) as well as a promising radiotherapy agent for the treatment for cancer. Currently, copper-64 suitable for biomedical studies is produced in the fast neutron flux trap (irradiation of zinc with fast neutrons) at the Missouri University Research Reactor. Access to the fast neutron flux trap is only possible on a weekly basis, making the availability of this tracer very limited. In order to significantly increase the availability of this intermediate-lived radiotracer, we have investigated and developed a method for the efficient production of high specific activity Cu-64 using a small biomedical cyclotron. It has been suggested that it may be possible to produce Cu-64 on a small biomedical cyclotron utilizing the 64Ni(p,n)64Cu nuclear reaction. We have irradiated both natural nickel and enriched (95% and 98%) Ni-64 plated on gold disks. Nickel has been electroplated successfully at thicknesses of approximately 20-300 mm and bombarded with proton currents of 15-45 microA. A special water-cooled target had been designed to facilitate the irradiations on a biomedical cyclotron up to 60 microA. We have shown that it is possible to separate Cu-64 from Ni-64 and other reaction byproducts rapidly and efficiently by using ion exchange chromatography. Production runs using 19-55 mg of 95% enriched Ni-64 have yielded 150-600 mCi of Cu-64 (2.3-5.0 mCi/microAh) with specific activities of 94-310 mci/microgram Cu. The cyclotron produced Cu-64 had been used to radiolabel PTSM [pyruvaldehyde bis-(N4-methylthiosemicarbazone), used to quantify myocardial, cerebral, renal, and tumor blood flow], MAb 1A3 [monoclonal antibody MAb to colon cancer], and octreotide. A recycling technique for the costly Ni-64 target material has been developed. This technique allows the nickel eluted off the column to be recovered and reused in the electroplating of new targets with an overall efficiency of greater than 90%.

Acute and chronic graft-versus-host disease after allogeneic peripheral-blood stem-cell and bone marrow transplantation: a meta-analysis

PURPOSE

Controversy exists as to whether the incidence of graft-versus-host disease (GVHD) is increased after peripheral-blood stem-cell transplantation (PBSCT) when compared with bone marrow transplantation (BMT). We performed a meta-analysis of all trials comparing the incidence of acute and chronic GVHD after PBSCT and BMT reported as of June, 2000. Secondary analyses examined relapse rates after the two procedures.

METHODS

An extensive MEDLINE search of the literature was undertaken. Primary authors were contacted for clarification and completion of missing information. A review of cited references was also undertaken. Sixteen studies (five randomized controlled trials and 11 cohort studies) were included in this analysis. Data was extracted by two pairs of reviewers and analyzed for the outcomes of interest. Meta-analyses, regression analyses, and assessments of publication bias were performed.

RESULTS

Using a random effects model, the pooled relative risk (RR) for acute GVHD after PBSCT was 1.16 (95% confidence interval [CI], 1.04 to 1.28; P=.006) when compared with traditional BMT. The pooled RR for chronic GVHD after PBSCT was 1.53 (95% CI, 1.25 to 1.88; P <.001) when compared with BMT. The RR of developing clinically extensive chronic GVHD was 1.66 (95% CI, 1.35 to 2.05; P <.001). The excess risk of chronic GVHD was explained by differences in the T-cell dose delivered with the graft in a meta-regression model that did not reach statistical significance. There was a trend towards a decrease in the rate of relapse after PBSCT (RR = 0.81; 95% CI, 0.62 to 1.05).

CONCLUSION

Both acute and chronic GVHD are more common after PBSCT than BMT, and this may be associated with lower rates of malignant relapse. The magnitude of the transfused T-cell load may explain the differences in chronic GVHD risk.

Radioactive 198Au-doped nanostructures with different shapes for in vivo analyses of their biodistribution, tumor uptake, and intratumoral distribution

With Au nanocages as an example, we recently demonstrated that radioactive (198)Au could be incorporated into the crystal lattice of Au nanostructures for simple and reliable quantification of their in vivo biodistribution by measuring the γ radiation from (198)Au decay and for optical imaging by detecting the Cerenkov radiation. Here we extend the capability of this strategy to synthesize radioactive (198)Au nanostructures with a similar size but different shapes and then compare their biodistribution, tumor uptake, and intratumoral distribution using a murine EMT6 breast cancer model. Specifically, we investigated Au nanospheres, nanodisks, nanorods, and cubic nanocages. After PEGylation, an aqueous suspension of the radioactive Au nanostructures was injected into a tumor-bearing mouse intravenously, and their biodistribution was measured from the γ radiation while their tumor uptake was directly imaged using the Cerenkov radiation. Significantly higher tumor uptake was observed for the Au nanospheres and nanodisks relative to the Au nanorods and nanocages at 24 h postinjection. Furthermore, autoradiographic imaging was performed on thin slices of the tumor after excision to resolve the intratumoral distributions of the nanostructures. While both the Au nanospheres and nanodisks were only observed on the surfaces of the tumors, the Au nanorods and nanocages were distributed throughout the tumors.

Quality of life associated with acute and chronic graft-versus-host disease

Acute and chronic graft-versus-host diseases (GVHD) are associated with increased morbidity and mortality after hematopoietic stem cell transplantation (HCT). We prospectively measured the quality of life (QOL) of patients undergoing allogeneic transplantation. Ninety-six subjects completed self-assessment surveys before HCT, and at 6 and/or 12 months post-HCT that included the Medical Outcomes Study Short Form 12 (SF12) and the Functional Assessment of Cancer Therapy-Bone Marrow Transplant scale. Eighty-three percent of survivors responded at 6 and 12 months. Physical and mental functioning assessed by the SF12 was not associated with either acute or chronic GVHD. In contrast, the trial outcome index (TOI) of the Functional Assessment of Cancer Therapy-Bone Marrow Transplant was sensitive to occurrence of either acute or chronic GVHD. GVHD is a major determinant of the long-term QOL of survivors. The adverse effects of acute GVHD are detectable with the TOI at 6 months post transplantation after which development of chronic GVHD is the most strongly correlated with worse QOL.

Consensus nomenclature rules for radiopharmaceutical chemistry - Setting the record straight

Over recent years, within the community of radiopharmaceutical sciences, there has been an increased incidence of incorrect usage of established scientific terms and conventions, and even the emergence of 'self-invented' terms. In order to address these concerns, an international Working Group on 'Nomenclature in Radiopharmaceutical Chemistry and related areas' was established in 2015 to achieve clarification of terms and to generate consensus on the utilisation of a standardised nomenclature pertinent to the field. Upon open consultation, the following consensus guidelines were agreed, which aim to.

Selective inhibition of STAT3 induces apoptosis and G(1) cell cycle arrest in ALK-positive anaplastic large cell lymphoma

Nucleophosmin-anaplastic lymphoma kinase (NPM-ALK) is an aberrant fusion gene product expressed in a subset of cases of anaplastic large cell lymphoma (ALCL). It has been shown that NPM-ALK binds to and activates signal transducer and activator of transcription 3 (STAT3) in vitro, and that STAT3 is constitutively active in ALK(+) ALCL cell lines and tumors. In view of the oncogenic potential of STAT3, we further examined its biological significance in ALCL using two ALK(+) ALCL cell lines (Karpas 299 and SU-DHL-1) and an adenoviral vector that carries dominant-negative STAT3 (AdSTAT3DN). Infection by AdSTAT3DN led to the expression of STAT3DN in both ALK(+) ALCL cell lines at a similar efficiency. Subcellular fractionation studies showed that a significant proportion of the expressed STAT3DN protein translocated to the nucleus, despite the fact that STAT3DN has a mutation at residue 705(tyrosine --> phenylalanine), a site that is believed to be crucial for STAT3 activation and nuclear translocation. Introduction of STAT3DN induced apoptosis and G(1) cell cycle arrest. Western blot studies showed that expression of STAT3DN resulted in caspase-3 cleavage, downregulation of Bcl-2, Bcl-xL, cyclin D3, survivin, Mcl-1, c-Myc and suppressor of cytokine signaling 3. These results support the concept that STAT3 activation is pathogenetically important in ALCL cells by deregulating the expression of multiple target proteins that are involved in the control of apoptosis and cell cycle progression.

Radioluminescent gold nanocages with controlled radioactivity for real-time in vivo imaging

Cerenkov luminescence imaging based on light emission from the decay of radionuclides has recently drawn great interest in molecular imaging. In this paper, we report for the first time the Cerenkov luminescence phenomenon of (198)Au isotope, as well as a facile route to the preparation of radioluminescent Au nanocages without additional radiolabeling or dye conjugation. The specific radioactivity of the Au nanocages could be easily and precisely controlled by varying the concentration of H(198)AuCl(4) precursor used for the galvanic replacement reaction. The direct incorporation of (198)Au atoms into the structure of Au nanocages enabled the ability of accurate analysis and real-time imaging in vivo. Furthermore, under biological conditions the radioactive Au nanocages were shown to emit light with wavelengths in the visible and near-infrared regions, enabling luminescence imaging of the whole mice in vivo, as well as the organs ex vivo. When combined with their favorable scattering and absorption properties in the near-infrared region, the radioactive Au nanocages can serve as a new platform for multimodality imaging and will have a significant impact on both small animal and clinical imaging.

Routine screening for psychosocial distress following hematopoietic stem cell transplantation

The diagnosis and treatment of cancer is often associated with high levels of psychosocial distress, yet exploration of these issues is rarely included in routine oncologic care. We conducted a pilot study to evaluate the feasibility of screening for psychosocial distress after autologous and allogeneic stem cell transplantation. A total of 80 adults were enrolled in Boston, MA, USA. Subjects completed self-administered assessments prior to hospital admission, at their first clinic visit after hospital discharge, and at 100 days post transplant. Assessments included validated instruments assessing psychosocial distress and quality of life (QOL). Elevated levels of anxiety and/or depression were detected in 55% of those providing pre-transplant assessments and were associated with compromised QOL. Post transplant screening was successfully performed in 69% of subjects and identified that 44% had symptoms of depression, anxiety or post traumatic stress disorder. Pre-transplant distress was associated with detection of distress after transplantation (81 vs 13%, P< 0.0001). In summary, we detected high levels of distress in transplant patients using self-administered tools. Pre-transplant distress appears to be highly predictive of distress post transplant and is a feasible marker to target screening and intervention programs.

High purity production and potential applications of copper-60 and copper-61

Previously we described the high yield production of 64Cu using a target system designed specifically for low energy, biomedical cyclotrons. In this study, the use of this target system for the production of 60Cu and 61Cu is described and the utility of these isotopes in the labeling of biomolecules for tumor and hypoxia imaging is demonstrated. 60Cu and 61Cu were produced by the 60Ni(p,n)60Cu, 61Ni(p,n)61Cu, and 60Ni(d,n)61Cu nuclear reactions. The nickel target (>99% enriched or natural nickel) was plated onto a gold disk as described previously (54-225 microm thickness) and irradiated (14.7 MeV proton beam and 8.1 MeV deuteron beam). The copper isotopes were separated from the nickel via ion exchange chromatography and the radioisotopic purity was assessed by gamma spectroscopy. Yields of up to 865 mCi of 60Cu have been achieved using enriched 60Ni. 61Cu has been produced with a maximum yield of 144 mCi using enriched 61Ni and 72 mCi using enriched 60Ni. Specific activities (using enriched material) ranged from 80 to 300 mCi/microg Cu for 60Cu and from 20 to 81 mCi/microg Cu for 61Cu. Bombardments of natural Ni targets were performed using both protons and deuterons. Yields and radioisotopic impurities were determined and compared with that for enriched materials. 60Cu was used to radiolabel diacetyl-bis(N4-methylthiosemicarbazone), ATSM. 60Cu-ATSM was injected into rats that had an occluded left anterior descending coronary artery. Uptake of 60Cu-ATSM in the hypoxic region of the heart was visualized clearly using autoradiography. In addition, 60Cu-ATSM was injected into dogs and excellent images of the heart and heart walls were obtained using positron emission tomography (PET). 61Cu was labeled to 1,4,8,11-tetraazacyclotetradecane-N,N',N",N"'-tetraacetic acid-octreotide (TETA-octreotide) and the PET images of tumor-bearing rats were obtained up to 2 h postinjection. After decay of the 61Cu, the same rat was injected with 64Cu-TETA-octreotide and the images were compared. The tumor images obtained using 61Cu were found to be superior to those using 64Cu as predicted based on the larger abundance of positrons emitted by 61Cu vs. 64Cu.

A large single-center experience with allogeneic stem-cell transplantation for peripheral T-cell non-Hodgkin lymphoma and advanced mycosis fungoides/Sezary syndrome

BACKGROUND

The prognosis for patients with most forms of T-cell lymphoma is poor. Allogeneic hematopoietic stem-cell transplantation (HSCT) may improve the outcome.

PATIENTS AND METHODS

This study examines the outcome of 52 patients who underwent ablative or nonablative allogeneic HSCT for peripheral T-cell lymphoma (PTCL) or advanced mycosis fungoides/Sezary syndrome over a 12-year period at a single institution. We divided the patients into those with predominantly nodal histologies: peripheral T-cell not otherwise specified (PTCL NOS), angioimmunoblastic (AITL), or anaplastic large cell lymphoma, T/null type (systemic) (ALCL), and predominantly extranodal histologies: natural killer (NK)/T cell, enteropathy type, hepatosplenic, subcutaneous panniculitic, mycosis fungoides, or T cell or NK cell other.

RESULTS

Median follow-up of survivors is 49 months. Non-relapse mortality and relapse at 3 years was 27% and 43%, respectively. The incidence of grade II-IV acute graft-versus-host disease (GVHD) was 21%. The incidence of extensive chronic GVHD at 2 years was 27%. The 3-year progression-free survival was 30%: 45% in patients with predominantly nodal histologies (PTCL NOS, AITL, and ALCL) and 6% in patients with predominantly extranodal histologies (P = 0.016). Overall survival at 3 years was 41% for all patients.

CONCLUSION

Allogeneic HSCT can produce long-term remissions in relapsed/refractory T-cell lymphoma, especially those with nodal histologies.

Comparative studies of Cu-64-ATSM and C-11-acetate in an acute myocardial infarction model: ex vivo imaging of hypoxia in rats

Copper labeled diacetyl-bis(N4-methylthiosemicarbazone) (Cu-ATSM) is a promising agent for the imaging of hypoxic tissues. In the present study 64Cu(t1/2 = 12.8 h) labeled Cu-ATSM was used in combination with 11C (t1/2 = 20.3 min) labeled acetate as a regional perfusion marker to visualize hypoxic rat heart tissue in an acute left anterior descending (LAD) coronary artery occluded rat model using an ex vivo tissue slice imaging technique. 64Cu-ATSM was injected intravenously c.a. 10 min after occlusion and rats were sacrificed by cervical dislocation 10 min after injection. Carbon-11-acetate was injected 1 min before sacrifice to obtain a measure of blood flow. The heart was dissected, frozen, and cut into 1-mm thick slices with a gauged slicer, and 11C images were obtained with an electronic autoradiography instrument. After decay of 11C, 64Cu images were obtained in the same manner. In ischemic regions, where there was low 11C accumulation, 64Cu showed high accumulation when compared with normal regions. In rats with a large occlusion, the center of the ischemia did not show any accumulation of either 11C or 64Cu, indicating no blood supply. Cu-ATSM appears to be useful for the detection of hypoxia with contrast being observed at short times (10 min) postinjection.

Nanocompatible Chemistry toward Fabrication of Target-Specific Gold Nanoparticles

Nanocompatible chemistry which utilizes a novel nontoxic phosphino amino acid as a reducing agent has resulted in the development of therapeutically useful gold nanoparticles under biologically benign media. Stabilization of gold nanoparticles by the edible gum arabic matrix has provided an effective pathway toward in vivo stable target-specific gold nanoparticles.

Current and potential therapeutic uses of lanthanide radioisotopes

In the last 25 years, diagnostic nuclear medicine has come to depend on the versatile chemistry of a single radioisotope, technetium-99m (Tc-99m). Different chelating molecules can be used to guide Tc-99m through various physiological pathways in the body to gain information about disease states. No single radioisotope similarly dominates therapeutic applications. In the field of radioisotope therapy, much discussion and debate have focused on what radioisotope might be "ideal" for treatment of malignant tumors. The ideal may not be a single radioisotope, but rather the class of very closely related radiolanthanides and lanthanide-like radioisotopes. These radioisotopes possess strikingly similar chemistries and thus all may be conjugated to biomolecules using a single chelate, the DOTA moiety (and its chemical analogs). They also provide a wide range of physical characteristics, such as half-lives and beta energies, that can be chosen to match the biological properties of the conjugated biomolecule and the malignant tumor. Thus, the radiolanthanide-DOTA bioconjugate model provides a set of physically diverse, but chemically very similar, therapeutic radiopharmaceutical agents, the individual members of which can be tailored to treat specific types of cancers.

Peripheral blood stem cells for allogeneic transplantation: a review

Peripheral blood stem cells (PBSCs) have become increasingly popular for use in hematopoietic stem cell transplantation. PBSCs are readily collected by continuous-flow apheresis from patients and healthy donors after the administration of s.c. recombinant colony-stimulating factors with only minimal morbidity and discomfort. Although the precise identification of PBSCs remains elusive, they can be phenotypically identified as a subset of all circulating CD34(+) cells. There are important phenotypic and biologic distinctions between PBSCs and bone marrow (BM)-derived progenitor cells. PBSCs express more lineage-specific antigens but are less metabolically active than their BM-derived counterparts. The use of PBSCs for allogeneic transplantation has been compared to BM in several randomized trials and cohort studies. The use of PBSCs in leukemia, myeloma, non-Hodgkin's lymphoma, and myelodysplasia has resulted in shorter times to neutrophil and platelet engraftment at the expense of increased rates of chronic graft-versus-host disease. The increase in graft-versus-host disease is mainly due to a log-fold increase in donor T cells transferred with the graft. Relapse rates after transplantation may be lower after PBSC transplantation but a convincing survival advantage has not been demonstrated overall. It is possible that a stronger graft-versus-tumor effect may exist with PBSCs when compared with BM although the mechanisms leading to this effect are not clear.

A combined analysis of the cystic fibrosis transmembrane conductance regulator: implications for structure and disease models

Over the past decade, nearly 1,000 variants have been identified in the cystic fibrosis transmembrane conductance regulator (CFTR) gene in classic and atypical cystic fibrosis (CF) patients worldwide, and an enormous wealth of information concerning the structure and function of the protein has also been accumulated. These data, if evaluated together in a sequence comparison of all currently available CFTR homologs, are likely to refine the global structure-function relationship of the protein, which will, in turn, facilitate interpretation of the identified mutations in the gene. Based on such a combined analysis, we had recently defined a "functional R domain" of the CFTR protein. First, presenting two full-length cDNA sequences (termed sCFTR-I and sCFTR-II) from the Atlantic salmon (Salmo salar) and an additional partial coding sequence from the eastern gray kangaroo (Macropus giganteus), this study went further to refine the boundaries of the two nucleotide-binding domains (NBDs) and the COOH-terminal tail (C-tail), wherein NBD1 was defined as going from P439 to G646, NBD2 as going from A1225 to E1417, and the C-tail as going from E1418 to L1480. This approach also provided further insights into the differential roles of the two halves of CFTR and highlighted several well-conserved motifs that may be involved in inter- or intramolecular interactions. Moreover, a serious concern that a certain fraction of missense mutations identified in the CFTR gene may not have functional consequences was raised. Finally, phylogenetic analysis of all the full-length CFTR amino acid sequences and an extended set of exon 13--coding nucleotide sequences reinforced the idea that the rabbit may represent a better CF model than the mouse and strengthened the assertion that a long-branch attraction artifact separates the murine rodents from the rabbit and the guinea pig, the other Glires.

Production and Supply of α-Particle-Emitting Radionuclides for Targeted α-Therapy

Encouraging results from targeted α-therapy have received significant attention from academia and industry. However, the limited availability of suitable radionuclides has hampered widespread translation and application. In the present review, we discuss the most promising candidates for clinical application and the state of the art of their production and supply. In this review, along with 2 forthcoming reviews on chelation and clinical application of α-emitting radionuclides, The Journal of Nuclear Medicine will provide a comprehensive assessment of the field.

Empty capsids in column-purified recombinant adenovirus preparations

Empty capsids from adenovirus, that is, virus particles lacking DNA, are well documented in the published literature. They can be separated from complete virus by CsCl density gradient centrifugation. Here we characterize the presence of empty capsids in recombinant adenovirus preparations purified by column chromatography. The initial purified recombinant adenovirus containing the p53 tumor suppressor gene was produced from 293 cells grown on microcarriers and purified by passage through DEAE-Fractogel and gel-filtration chromatography. Further sequential purification of the column-purified virus by CsCl and glycerol density gradient centrifugations yielded isolated complete virus and empty capsids. The empty capsids were essentially noninfectious and free of DNA. Analysis of empty capsids by SDS-PAGE or RP-HPLC showed the presence of only three major components: hexon, IIIa, and a 31K band. This last protein was identified as the precursor to protein VIII (pVIII) by mass spectrometric analysis. No pVIII was detected from the purified complete virus. Analysis by electron microscopy of the empty capsids showed particles with small defects. The amount of pVIII was used to determine the level of empty capsid contamination. First, the purified empty capsids were used to quantify the relation of pVIII to empty capsid particle concentration (as estimated by either light scattering or hexon content). They were then used as a standard to establish the empty capsid concentration of various recombinant adenovirus preparations. Preliminary research showed changes in empty capsid concentration with variations in the infection conditions. While virus purification on anion-exchange or gel-filtration chromatography has little effect on empty capsid contamination, other chromatographic steps can substantially reduce the final concentration of empty capsids in column-purified adenovirus preparations.

Sirolimus for GVHD prophylaxis in allogeneic stem cell transplantation

Sirolimus is a novel macrolide immunosuppressant widely used in solid organ transplantation. We have conducted three clinical trials using this compound as prophylaxis against GVHD after allogeneic stem cell transplantation. Our studies have demonstrated excellent GVHD control even when mismatched and unrelated donors were used. The morbidity and mortality associated with transplantation were reduced due to the omission or reduction in methotrexate dose. Furthermore, CMV reactivation and fungal infection rates were low. However, we have noted that sirolimus may be associated with increased rates of thrombotic microangiopathy after transplantation. Sirolimus has other uses, such as the treatment of established acute and chronic GVHD, and may be useful for treatment of post transplant lymphoproliferative disorder and perhaps as an antineoplastic agent against a wide variety of hematologic and solid neoplasms.

Development of an in vitro model for assessing the in vivo stability of lanthanide chelates

An in vitro model was developed to evaluate the in vivo stability of lanthanide polyaminocarboxylate complexes. The ligand-to-metal ratios for the chelates EDTA, CDTA, DTPA, MA-DTPA (monoamide-DTPA) and DOTA with the lanthanides lanthanum, samarium, and lutetium were optimized to achieve > or = 98% complexation yield for the resultant radiolanthanide complexes. The exchange of the radiolanthanides from their EDTA, CDTA, DTPA, MA-DTPA and DOTA complexes with Ca(2+) was determined by in vitro adsorption and in vitro column studies using hydroxyapatite (HA), an in vitro bone model. In vitro serum stability of these radiolanthanide complexes was used as an additional indicator of in vivo stability, although the mechanism of instability in serum will be different than with bone. The in vitro studies were consistent with the expected findings that the smallest lanthanide (Lu) formed the most stable complexes. In vivo studies were done to validate the in vitro model. Biodistribution studies in normal CF-1 mice showed that in vivo stability of the complex (i.e., the more lanthanide remaining in complex form) could be assessed by a combination of the urinary, bone and liver uptake. For example, biodistribution studies demonstrate that high urinary excretion correlated with complex stability, while high liver plus bone uptake correlated with complex instability. The urinary excretion of the EDTA complexes decreased from (177)Lu to (140)La indicating a loss in stability in the direction of (140)La, consistent with the in vitro studies. The more stable a lanthanide complex is, the lower its exchange with HA in vitro will be, and the lower its combined bone plus liver uptake and higher its urinary excretion will be in vivo. This investigation indicates that the in vivo stability can be determined by a screening method that measures the degree of exchange from the lanthanide chelate with hydroxyapatite (HA) and its serum stability.

The Impact of Positron Range on PET Resolution, Evaluated with Phantoms and PHITS Monte Carlo Simulations for Conventional and Non-conventional Radionuclides

PURPOSE

The increasing interest and availability of non-standard positron-emitting radionuclides has heightened the relevance of radionuclide choice in the development and optimization of new positron emission tomography (PET) imaging procedures, both in preclinical research and clinical practice. Differences in achievable resolution arising from positron range can largely influence application suitability of each radionuclide, especially in small-ring preclinical PET where system blurring factors due to annihilation photon acollinearity and detector geometry are less significant. Some resolution degradation can be mitigated with appropriate range corrections implemented during image reconstruction, the quality of which is contingent on an accurate characterization of positron range.

PROCEDURES

To address this need, we have characterized the positron range of several standard and non-standard PET radionuclides (As-72, F-18, Ga-68, Mn-52, Y-86, and Zr-89) through imaging of small-animal quality control phantoms on a benchmark preclinical PET scanner. Further, the Particle and Heavy Ion Transport code System (PHITS v3.02) code was utilized for Monte Carlo modeling of positron range-dependent blurring effects.

RESULTS

Positron range kernels for each radionuclide were derived from simulation of point sources in ICRP reference tissues. PET resolution and quantitative accuracy afforded by various radionuclides in practicable imaging scenarios were characterized using a convolution-based method based on positron annihilation distributions obtained from PHITS. Our imaging and simulation results demonstrate the degradation of small animal PET resolution, and quantitative accuracy correlates with increasing positron energy; however, for a specific "benchmark" preclinical PET scanner and reconstruction workflow, these differences were observed to be minimal given radionuclides with average positron energies below ~ 400 keV.

CONCLUSION

Our measurements and simulations of the influence of positron range on PET resolution compare well with previous efforts documented in the literature and provide new data for several radionuclides in increasing clinical and preclinical use. The results will support current and future improvements in methods for positron range corrections in PET imaging.