Barbara J. Hughey

Production and purification of gallium-66 for preparation of tumor-targeting radiopharmaceuticals

Gallium-66 (T(1/2) = 9.49 h) is an intermediate-lived radionuclide that has potential for positron emission tomography (PET) imaging of biological processes with intermediate to slow target tissue uptake. We have produced (66)Ga by the (66)Zn(p,n) (66)Ga nuclear reaction using a small biomedical cyclotron and have investigated methods for purifying (66)Ga that could be applied to the development of an automated processing system. Measured yields of (66)Ga were very high with a production yield of nearly 14 mCi/microA-h at 14.5 MeV bombardment energy, a value in excellent agreement with theoretical predictions based on literature cross sections for the (66)Zn(p,n) (66)Ga reaction. Gallium-66 has been purified from irradiated zinc targets two ways, by cation-exchange chromatography and diisopropyl ether extraction. The concentrations of stable contaminants in (66)Ga following the two processing methods were determined, and it was found that iron and zinc were present at levels up to an order of magnitude higher after cation-exchange chromatography. The bioconjugates DOTA-Tyr(3)-octreotide and DOTA-biotin were labeled with (66)Ga purified by both methods. Following purification of (66)Ga by solvent extraction, radiochemical yields in excess of 85% were obtained for both compounds, in contrast to much lower labeling yields (less than 20%) obtained after the cation-exchange separation. Higher concentrations of stable contaminants likely contributed to the poor radiochemical yields for labeling DOTA-Tyr(3)-octreotide and DOTA-biotin with cation-exchanged (66)Ga. The lower purity and radiolabeling yields obtained using cation-exchange do not warrant the development of an automated processing system based on this method. Therefore, work is in progress to automate the diisopropyl ether extraction method for routine processing of (66)Ga.

Low-energy biomedical GC–AMS system for 14C and 3H detection

Abstract The use of accelerator mass spectrometry (AMS) in biomedical research will require the development of cost-effective, laboratory-sized AMS systems that can be used in conjunction with gas and liquid phase separation techniques. This paper describes a prototype GC–AMS system designed for the detection of 14C and 3H in organic samples. The entire AMS system including the injector, ion source, tandem accelerator, and high-energy analyzer is approximately 3.5 m wide, 1.5 m high and 1 m deep. Also described are methods for converting gas chromatograph (GC) effluent to gaseous CO2 for 14C-labeled compounds. A gas-fed cesium (Cs) sputter ion source converts the CO2 into C− for injection into the AMS accelerator, allowing on-line analysis of 14C-labeled biological samples with AMS.

Design of a compact 1 MV AMS system for biomedical research

Abstract The widespread use of accelerator mass spectrometry in biomedical research will require the development of cost-effective, laboratory-sized AMS systems which can be used in conjunction with conventional gas and liquid phase separation techniques. This paper describes the design of a low energy AMS system for the detection of 14C and 3H in labeled biological samples. The system utilizes a compact 1 MV tandem accelerator which incorporates a foil stripper. The low energy analyzer, accelerating column, and high energy analyzer are designed for efficient transport and analysis of both carbon and hydrogen beams using the minimum number of optical elements. The resulting instrument is very compact: the entire AMS system including the injector, ion source and high energy analyzer is just under 3 m wide and is approximately 1.3 m high and 1 m deep. The relatively small size of this system will allow its installation in most biomedical laboratory facilities. The system is predicted to provide a statistical precision of better than 2% for the quantitation of attomole samples.

Positron beam production with a deuteron accelerator

Abstract A graphite target was bombarded with 1.5 MeV deuterons, producing the isotope 13 N, which is a positron emitter. Using the activated material a slow positron beam with an intensity of 0.7 (0.14)×10 5 s −1 was produced. A (saturated) 13 N yield of 63 (11) MBq/μA was observed, with 1.5 MeV deuterons, which is consistent with previous calculations and experiments. Our results show that, with the method we outline, positron beams with an average intensity of up to 1×10 8 s −1 may be produced.

A windowless 13N production target for use with low energy deuteron accelerators

The recent development of low energy accelerators for positron emission tomography has necessitated the development of new targets for 13N production. 12C(d,n)13N reaction yields in graphite at low deuteron beam energies (0.8-3.2 MeV) are presented and a new technique for the in situ extraction of 13N activity from solid graphite and subsequent conversion to [13N] ammonia is described. The target is windowless and is reusable for multiple isotope production runs. This technique utilizes radio frequency induction heating to rapidly heat the graphite to combustion temperatures in an O2 gas stream. The conversion of activity induced in the target to [13N] ammonia in under 10 min with an overall decay-corrected efficiency of 45% is reported.

Production of [13N]ammonia applicable to low energy accelerators.

We have developed a technique for the rapid conversion of the nitrogen-13 induced in a graphite target into nitrogen oxides. This was accomplished by heating the graphite target in a stream of pure oxygen at 800 degrees C. Less than 20% of the radioactivity was found in the form of [13N]nitrogen. The rest of the radioactivity was efficiently trapped in a solid-phase medium that consisted of an aqueous solution of 5% NaOH dispersed in silica gel. The radioactivity from this solid-phase medium was eluted with water (94% recovery) and found to be in the form of 13NO2- (99%). This was subsequently converted to [13N]ammonia with Raney-nickel, either by a conventional liquid-phase reduction with an overall conversion efficiency to ammonia of 45%, or by an incorporation of the Raney-nickel into the solid-phase medium. The latter system resulted in an overall conversion efficiency to ammonia of 37 +/- 9%, with a radiochemical purity of nearly 100% and a synthesis time under 17 min.

Beyond the lab report: The place of student-designed research and visual communication in a mechanical engineering fundamentals course

Student-designed research projects are more meaningful and more similar to professional experiences when they are embedded in a sequence of technical and communication tasks that approximate the evolution of a real-world research project. Instructors part of a mechanical engineering fundamentals course at the Massachusetts Institute of Technology describe an innovative, semester-long student project known as “Go Forth and Measure,” which prompts students to design, propose, and conduct an original study and communicate its progress and findings through several professional genres interspersed through the term. Sound data and error analysis, effective graphic communication, and professional practices are emphasized in all tasks. Lab instructors and communication instructors, led by technical faculty, coordinate the teaching of a thoughtful sequence of activities. Approaches to teaching the deliberate crafting of the story of data - in a figure, in a research poster - are described here, and preliminary observations on student work and their experience are summarized.

MICA: an innovative approach to remote data acquisition

Laboratory-based instruction in engineering and physics education often involves activities in which students learn how various sensors and actuators function and how to analyze the data collected. A key requirement for this learning experience to be effective is the ready availability of a broad range of sensors that can be coupled to software and hardware environments with minimal set-up so measurements can be made and analyzed within a reasonable period of time. However, most sensors currently available for this purpose are connected to the data acquisition system via wires which interfere with many of the measurements students want to take, particularly those involving moving parts. Additionally, most existing measurement systems used in laboratory courses cannot generate input variables while measuring the resulting output variables, thus relegating the measurement system to a passive role and eliminating the opportunity for instruction in feedback systems.

A split high‐Q superconducting cavity

We describe the construction of a 35‐GHz split high‐Q superconducting cavity operating in the TM010 mode. The cavity is tuned by varying the spacing between the halves. Radiation loss from this gap is suppressed by a choke groove. Q=4×107 has been achieved in both lead‐plated copper and niobium cavities at a temperature of 2 K. Q>107 can be maintained over a 300‐MHz tuning range, corresponding to a gap between the halves of 85 μm.

Atom-Photon Interaction Modified by a Microwave Cavity

We present preliminary results on the modification of atomic emission properties in a high Q cavity. A cavity mistuned from an atomic transition will inhibit the absorption and emission rates of that transition.1 A tuned cavity enhances the absorption and emission rates above their free space values. For a cavity with a sufficiently long damping time (high Q), there will be an oscillatory exchange of energy between the atom and the cavity. It is this regime of the atom-cavity interaction that we will discuss in this paper. An article by Haroche2 provides a good background for the theoretical and experimental aspects of this work. Highly excited (Rydberg) states of atoms are well suited to these experiments because they have long lifetimes and large dipole matrix elements between neighboring states with transitions at microwave frequencies. One- and two-photon micromasers 3,4 employing Rydberg atoms in microwave cavities have recently been observed. Collapse and revival of the atom-cavity system, as described by Eberly et al.,5 has been observed in a one-atom maser.6 The experimental system described in this paper employs a different type of cavity from those used in other experiments. We have chosen a “split” cavity design to give us better time resolution and allow us to examine the atom-cavity interaction at short times. The disadvantage of our method is that it is more difficult to achieve high Q in a split cavity. However, we have achieved Q > 107, which is more than sufficient to observe the one-atom oscillations in the cavity.