Collapse of the hyperfine magnetic field at the Ru site in ferromagnetic rare earth intermetallics

The M\"{o}ssbauer Effect(ME) is frequently used to investigate magnetically ordered systems. One usually assumes that the magnetic order induces a hyperfine magnetic field, $B_{hyperfine}$, at the ME active site. This is the case in the ruthenates, where the temperature dependence of $B_{hyperfine}$ at $^{99}$Ru sites tracks the temperature dependence of the ferromagnetic or antiferromagnetic order. However this does not happen in the rare-earth intermetallics, GdRu$_2$ and HoRu$_2$. Specific heat, magnetization, magnetic susceptibility, M\"{o}ssbauer effect, and neutron diffraction have been used to study the nature of the magnetic order in these materials. Both materials are found to order ferromagnetically at 82.3 and 15.3 K, respectively. Despite the ferromagnetic order of the rare earth moments in both systems, there is no evidence of a correspondingly large $B_{hyperfine}$ in the M\"{o}ssbauer spectrum at the Ru site. Instead the measured spectra consist of a narrow peak at all temperatures which points to the absence of magnetic order. To understand the surprising absence of a transferred hyperfine magnetic field, we carried out {\it ab initio} calculations which show that spin polarization is present only on the rare-earth site. The electron spin at the Ru sites is effectively unpolarized and, as a result, $B_{hyperfine}$ is very small at those sites. This occurs because the 4$d$ Ru electrons form broad conduction bands rather than localized moments. These 4$d$ conduction bands are polarized in the region of the Fermi energy and mediate the interaction between the localized rare earth moments.Comment: 34 pages -Revtex + 17 ps figure

Routine synthesis of N-[11C-methyl]scopolamine by phosphite mediated reductive methylation with [11C]formaldehyde

A synthesis of [11C]scopolamine capable of clinical delivery of this agent in high specific activity is described. The precursor [11C]formaldehyde was produced by catalytic oxidation of [11C]CH3OH over metallic silver and was used to N-11C-methylate norscopolamine using aqueous neutral potassium phosphite as the reducing agent. The labeling reaction was complete after 5 min at 75-80[deg]C and the [11C]scopolamine (99% radiochemical purity) was isolated by preparative HPLC. Total synthesis time is less than 45 min. Decay corrected radiochemical yields from [11C]CO2 are presently 20-43%.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/27552/1/0000596.pd

Extraction of [18F]fluoride from [18O]water by a fast fibrous anion exchange resin

[18F]Fluoride for nucleophilic radiofluorination was recovered from target water by trapping on a fibrous anion exchange resin in the hydroxide form and subsequent displacement into wet methanolic K2CO3. Extraction into methanol facilitated rapid evaporation and resolubilization of the [18F]fluoride as an ion pair. The resin was first dried in situ and rehydrated with [18O]H2O to avoid isotopic dilution of the target water.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/28900/1/0000737.pd

Ion exchange reaction of [18F]fluoride with an oxidized carbon surface

[18F]Fluoride was trapped from [18O]water in high yield by ion exchange on a microporous carbon prepared by controlled oxidation to produce a cationic surface with an exchange capacity of about 350 [mu] equiv/g. The [18F]fluoride could be recovered by displacement with aqueous K2CO3. The cationic carbon offered a dimensionally rigid matrix of high thermal stability. It was characterized with respect to chemical reactivity and selectivity for anion exchange.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/29626/1/0000715.pd

Routine production of 2-deoxy-2-[18F]fluoro--glucose by direct nucleophilic exchange on a quaternary 4-aminopyridinium resin

Resin-supported [18F]fluoride ion has been prepared and applied to a rapid, convenient synthesis of [18F]FDG. "No-carrier-added" [18F]fluoride ion is collected on a quaternary 4-(N, N-dialkylamino)-pyridinium functionalized polystyrene anion exchange resin directly from a [18O]water target, dried by rinsing with acetonitrile, and then reacted with 1,3,4,6-tetra-O-acetyl-2-O-trifluoromethanesulfonyl-[beta]--mannopyrannose. Acidic hydrolysis yields [18F]FDG in a synthesis time of 40 min with overall yields presently averaging above 50%.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/28859/1/0000694.pd

Multiphase extraction: Rapid phase-transfer of [18F]fluoride ion for nucleophilic radiolabeling reactions

In multiphase extraction [18F]fluoride ion for radiolabeling is recovered from target water by passage through a small column of microporous polymer impregnated with a lipophilic cryptand or quaternary ammonium salt. The 18O enriched water can be recovered for reuse. The [18F]fluoride ion-pair is eluted from the column by a small volume of acetonitrile or other organic solvent. Evaporation of the acetonitrile removes traces of water to yield a reactive ion pair for nucleophilic radiofluorination reactions. A wide range of ion-pairs based on K+ or NH4+ cryptands or quaternary ammonium salts can be employed. The method was applied to the synthesis of [18F]FDG.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/27603/1/0000647.pd

Direct simultaneous production of [15O]water and [13N]ammonia or [18F]fluoride ion by 26 MeV proton irradiation of a double chamber water target

A simple double liquid chamber target was developed to provide the option for simultaneous production of [15O]H2O and either 13N or 18F using a single proton beam. Irradiation of natural water in a thin aluminium front chamber produced [15O]H2O by the 16O(p, pn)15O reaction directly. Large (0.5-1.0 Ci) doses of sterile [15O]H2O (> 99.95% radionuclide purity) were routinely prepared in 1 min from end of 20 [mu]A bombardments using this target and an in-line mixed bed ion exchange column purification. Water in the thin front chamber degraded proton energies on exit to 20-18 MeV. The rear silver liquid chamber was threefold thick to 17 MeV protons in water and it efficiently produced either 13N by the 16O(p, [alpha])13N reaction or [18F]fluoride ion by the 18O(p, n)18F reaction. Both target chambers were overpressurized with at least 6 atm of gas to minimize boiling/cavitation of water at high beam currents. Using hydrogen as the overpressure gas on the back chamber and an in-line anion exchange column radionuclidic cleanup process, high yields of sterile, aqueous [13N]NH3 (40-200 mCi; 20 [mu]A) were produced directly from the back chamber at the same time that [15O]H2O was being produced from the front chamber. The combination of this target system with a cyclotron capable of generating 26-30 MeV protons provides great flexibility and simplicity for rapid, high volume production of the three best validated and most widely used radiopharmaceuticals at the present time in clinical positron emission tomography: [15O]H2O, [13N]NH3 and [18F]FDG.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/28943/1/0000780.pd

A captive solvent method for rapid N-[11C]methylation of secondary amides: Application to the benzodiazepine, 4'-chlorodiazepam (RO5-4864)

[11C]4'-Chlorodiazepam (RO5-4864), for PET studies of peripheral benzodiazepine receptors, was synthesized by alkylation of 1-desmethyl-4'-chlorodiazepam, in a small volume of acetone adsorbed on acrylic yarn, with [11C]methyl iodide in the injection loop of a liquid chromatograph. The reaction mixture was introduced directly onto a small, disposable alumina chromatographic column. Elution with pentane:ethanol gave a product of high chemical and radiochemical purity. A simple heating and cooling device for the injection loop is described.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/27565/1/0000609.pd

Recovery and purification of no-carrier-added [18F]fluoride with bistrimethylsilylsulfate (BTMSS)

No-carrier-added trimethylsilyl[18F]fluoride (TMS[18F]F) was rapidly liberated from a variety of dry supports containing unreactive [18F]fluoride by simply heating with neat bistrimethylsilylsulfate. The supports included calcium phosphate, anion exchange resins, alumina, borosilicate and porous carbon beads, to which [18F]fluoride was applied by absorption or evaporation of aqueous solution. TMS[18F]F was evolved essentially free of entrained moisture or excess silylating agent and was efficiently absorbed and rapidly cleaved to free [18F]fluoride ion by 0.1% benzyltrimethylammonium methoxide in anhydrous methanol. Passage of this solution through a strong cation exchange column provided purified hydrogen[18F]fluoride, which was subsequently trapped on a quaternary 4-aminopyridinium resin and used for heterogeneous nucleophilic radiofluorination of 1,3,4,6-tetraacetyl-beta-mannopyranose-2-triflate in 70% yield. The purified [18F]fluoride was also used for solution phase nucleophilic labeling of ethyl [18F]4-fluorobenzoate following addition of K2CO3/Kryptofix and DMSO. This approach provides a simplified way to ensure high reactivity in [18F]fluoride ion from cyclotron targets. It also may be used to salvage active [18F]fluoride ion from insoluble complexes and radiofluorination reaction residues.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/29654/1/0000743.pd

Regional 2-[ 18 F]fluoro-2-deoxy- d -glucose uptake varies in normal lung

2-[ 18 F]fluoro-2-deoxy- d -glucose positron emission tomography (FDG-PET) is a promising imaging procedure for detecting primary and metastatic cancer in the lungs. We have, however, failed to detect some small tumors in the lower lobes of the lungs. This study aimed to determine whether increase 18 F background activity in the dependent lower lungs is present, which could make lesion detection more difficult. We measured the standardized uptake values (SUVs) for FDG of normal lung remote from the nodular lesion in 16 patients with newly diagnosed untreated lung lesions stronlgy suspected to represent non-small cell lung cancers. In addition, 15 patients with known or suspected primary breast cancers without pulmonary lesions were included as control subjects. After PET transmission images of the thorax were obtained, approximately 370 MBq of FDG was injected intravenously and imaging was immediately begun. Patients were supine throughout the study. SUVs were determined with images obtained 50–70 min after FDG injection. Regions of interest (ROls) of 6×6 pixels were positioned over normal lung in anterior, mid, and posterior portions of upper, middle, and lower lung fields. Thus, as many as 18 ROls were positioned in each patient. The SUVs of the posterior portion were significantly higher than those of the anterior and mid portions in the population of 31 cases ( P <0.001). Also, the mean SUV of the lower lung field was significantly higher than the SUVs of the upper and middle lung fields in this population ( P <0.01). This pattern was seen among the two groups of 16 patients suspected of having lung cancer and 15 control subjects. Background 18 F activity was highest in posterior and lower lung in these patients. The maximum value of mean SUV observed in normal posterior lower lung was 0.804±0.230 (41% greater than the mean SUV in the anterior upper lung), which is in the range of the apparent SUV for a 5-mm lung lesion, with higher SUV, due to recovery coefficient issues. Thus this phenomenon could contribute to occasional false-negative lesions in those areas. Increased blood flow and FDG delivery and also scatter from heart and liver may contribute to the increased lower lung background activity. Regional differences in normal lung FDG uptake are significant and should be considered when interpreting pulmonary PET studies in patients with suspected primary or metastatic lung cancer.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/46841/1/259_2004_Article_BF00833385.pd