Frequency conversion of microwave signal without direct bias current using nanoscale magnetic tunnel junctions

Frequency conversion forms an integral block of the electronic circuits used in various applications including energy harvesting, communications and signal processing. These frequency conversion units however require external power sources and occupy a large device footprint making it difficult to be integrated in micro-circuits. Here we demonstrate that nanoscale magnetic tunnel junctions can act as frequency converters without an external power supply or DC bias source. The device directly mixes an external microwave signal with the internal spin precession oscillations to create new frequencies tunable by an external magnetic field in a single device with a small device footprint. We observe up-conversion and down-conversion of the input signal for excitation frequencies between 2 GHz and 6 GHz. We also show that the device acts as a zero-bias rectifier that can generate voltages exceeding 12 mV when the excitation frequency matches the natural oscillations mode of the device.

Toxicology study for magnetic injection of prednisolone into the rat cochlea

This paper investigates the safety of a novel 'magnetic injection' method of delivering therapy to the cochlea, in a rodent model. In this method of administration, a magnetic field is employed to actively transport drug-eluting superparamagnetic iron-oxide core nanoparticles into the cochlea, where they then release their drug payload (we delivered the steroid prednisolone). Our study design and selection of control groups was based on published regulatory guidance for safety studies that involve local drug delivery. We tested for both single and multiple delivery doses to the cochlea, and found that magnetic delivery did not harm hearing. There was no statistical difference in hearing between magnetically treated ears versus ears that received intra-tympanic steroid (a mimic of a standard-of-care for sudden sensorineural hearing loss), both 2 and 30 days after treatment. Since our treatment is local to the ear, the levels of steroid and iron circulating systemically after our treatment were low, below mass-spectrometry detection limits for the steroid and no different from normal for iron. No adverse findings were observed in ear tissue histopathology or in animal gross behavior. At 2 and 30 days after treatment, inflammatory changes examined in the ear were limited to the middle ear, were very mild in severity, and by day 90 there was ongoing and almost complete reversibility of these changes. There were no ear tissue scarring or hemorrhage trends associated with magnetic delivery. In summary, after conducting a pre-clinical safety study, no adverse safety issues were observed.

Magnetic microkayaks: propulsion of microrods precessing near a surface by kilohertz frequency, rotating magnetic fields

Surface-swimming nano- and micromotors hold significant potential for on-chip mixing, flow generation, sample manipulation, and microrobotics. Here we describe rotating microrods magnetized nearly orthogonally to their long axes. When actuated near a solid surface, these microrods demonstrate precessing motion, with rods describing a double cone similar to the motion of a kayaker's paddle. The precessing motion induces translation. At 1 kHz, these "microkayaks" move at translational velocities of ≈14 μm s^-1 and generate advective flows up to 10 μm s^-1.

Dynamic inversion enables external magnets to concentrate ferromagnetic rods to a central target

The ability to use magnets external to the body to focus therapy to deep tissue targets has remained an elusive goal in magnetic drug targeting. Researchers have hitherto been able to manipulate magnetic nanotherapeutics in vivo with nearby magnets but have remained unable to focus these therapies to targets deep within the body using magnets external to the body. One of the factors that has made focusing of therapy to central targets between magnets challenging is Samuel Earnshaw's theorem as applied to Maxwell's equations. These mathematical formulations imply that external static magnets cannot create a stable potential energy well between them. We posited that fast magnetic pulses could act on ferromagnetic rods before they could realign with the magnetic field. Mathematically, this is equivalent to reversing the sign of the potential energy term in Earnshaw's theorem, thus enabling a quasi-static stable trap between magnets. With in vitro experiments, we demonstrated that quick, shaped magnetic pulses can be successfully used to create inward pointing magnetic forces that, on average, enable external magnets to concentrate ferromagnetic rods to a central location.

Porous Silicon-Based Quantum Dot Broad Spectrum Radiation Detector

Silicon is a convenient and inexpensive platform for radiation detection, but has low stopping power for x-rays and gamma-rays with high energy (e.g., 100 keV, as used in computed tomography and digital radiography, or 1 MeV, as desired for detection of nuclear materials). We have effectively increased the stopping power of silicon detectors by producing a layer of porous or micro-machined silicon, and infusing this layer with semiconductor quantum dots made of electron-dense materials. Results of prototype detectors show sensitivity to infrared, visible light, and x-rays, with dark current of less than 1 nA/mm².

Preparation of F-18 labeled annexin V: a potential PET radiopharmaceutical for imaging cell death

The clinical response to antitumor therapy is measured using imaging, such as CT or MRI, 6-12 weeks following chemotherapy treatment. The images at that time reflect both tumor cell death and new growth. Therefore, the amount of tumor cell death caused by chemotherapy cannot be efficiently quantified with current imaging modalities. A quantitative measurement of tumor cell death immediately following chemotherapy is needed to help validate both new agents and to optimize administration of existing therapies. Annexin V is a 36kD protein that binds to exposed phosphatidylserine (PS) on dying cells. In order to synthesize a probe that can detect cell death in vivo, the positron emitter F-18 was conjugated to annexin V via the compound N- succinimidyl-4-[18F]fluorobenzoate, [18F]SFB. The decay corrected radiochemical yield of F-18 labeled annexin V from 18F fluoride was 17.6 +/- 5.6% (n = 4) in three hours. The stepwise radiochemical yield of the conjugation step with annexin V was as high as 70% when a protein concentration of 5 mg/ml was used. Cancer cells treated with the chemotherapeutic agent, etoposide, showed an 88% increase in the binding of F-18 labeled annexin V compared to untreated cells. We conclude that [18F] labeled annexin V can be readily prepared by the conjugation of annexin V with [18F]SFB and that the positron-emitting compound is biologically active in detecting apoptosis.

Segmentation algorithms for detecting microcalcifications in mammograms

The presence of microcalcification clusters in mammograms contributes evidence for the diagnosis of early stages of breast cancer. In many cases, microcalcifications are subtle and their detection can benefit from an automated system serving as a diagnostic aid. The potential contribution of such a system may become more significant as the number of mammograms screened increases to levels that challenge the capacity of radiology clinics. Many techniques for detecting microcalcifications start with a segmentation algorithm that indicates all candidate structures for the subsequent phases. Most algorithms used to segment microcalcifications have aspects that might raise operational difficulties, such as thresholds or windows that must be selected, or parametric models of the data. We present a new segmentation algorithm and compare it to two other algorithms: the multi-tolerance region growing algorithm that operates without the aspects mentioned above, and the active contour model that has not been applied previously to segment microcalcifications. The new algorithm operates without threshold or window selection, or parametric data models, and it is more than an order of magnitude faster than the other two.

Single tube gamma camera for scintimammography

The development of large area Position Sensitive Photo Multiplier Tubes (PSPMT) by Hamamatsu is opening new imaging possibilities in Nuclear Medicine. In particular the realization of the 8" PSPMT prototype represents the first important technological advantage since the discovery of the Anger Camera. PSPMT virtually integrates in one hundreds PMT allowing the creation of dedicated detectors. A Single Tube Gamma Camera based on a 5" PSPMT dedicated to scintimammography is presented and discussed in this work. To optimize gamma camera response two different scintillating arrays were tested: YAP:Ce and CsI (Tl). Their overall size cover all photocathode active area, and crystal pixel size was 2 mm x 2 mm. The detection efficiency was comparable to that of Anger Camera. The best result was obtained by CsI (Tl) scintillating: an intrinsic spatial resolution of 1.6 mm FWHM and a relative energy resolution of 17% FWHM. New image possibilities in scintimammography are offered by Single Tube Gamma Camera operating in the same radiological projection of RX mammography.

The role of Compton background and breast compression on cancer detection in scintimammography

99mTc MIBI scintimammography is a promising diagnostic technique for cancer detection. Using a dedicated Small Field Of View Gamma Camera (SFOVGC) with the high spatial resolution recently developed, it is possible to improve the sensitivity and to achieve images in projections similar to mammography with the breast under moderate compression. This new technique is called Single Photon Emission Mammography (SPEM). Several factors affect the imaging of small cancers; breast thickness, tumor-collimator distance and body activity. A phantom study was performed to assess the role of breast compression in scintimammography. In this work we analyze the intensity and the energy distribution of Compton scattering affecting the breast scintigraphy, by a Germanium detector and by SFOVCG. Five patients with 7 to 18 mm sized cancer were studied. The intensity of Compton scattering resulted from 4 to 10 times greater than true events. The fundamental role played by breast compression to improve the scintimammographic sensitivity is discussed.

99mTc MIBI scintimammography with a high resolution single tube gamma camera: preliminary study

99mTc MIBI scintimammography is a sensitive and specific diagnostic technique for breast cancer detection when cancers more than 1 cm sized are considered. However the sensitivity falls in the case of submillimetric lesions. We developed a new Small Field of View, High Resolution Detector, able to image the breast in similar conditions of x-ray mammography: it allows the performance of Single Photon Emission Mammography (SPEM) studies. Seven patients with suspicion of malignant lesions were comparatively submitted to a Prone Scintimammography (PSM) by Anger camera and to a cranio-caudal view SPEM. The final diagnosis was reached by histopathology. Four malignant lesions were identified by SPEM but not by PSM, which that failed to image two submillimetric cancers. Both the cameras gave normal findings for benign lesions, confirming the high sensitivity of this technique. The results allow us to consider the SPEM camera as promising to improve scintimammographic sensitivity, even when small-sized tumors are examined.

Feasibility study for positron emission mammography

A feasibility study is presented for a small, low-cost, dedicated device for positron emission mammography. Two detector arrays above and below the breast would be placed in a conventional mammography unit. These detectors are sensitive to positron annihilation radiation, and are connected to a coincidence circuit and a multiplane image memory. Images of the distribution of positron-emitting isotope are obtained in real time by incrementing the memory location at the intersection of each line of response. Monte Carlo simulations of a breast phantom are compared with actual scans of this phantom in a conventional PET scanner. The simulations and experimental data are used to predict the performance of the proposed system. Spatial resolution experiments using very narrow bismuth germanate BGO crystals suggest that spatial resolutions of about 2 mm should be possible. The efficiency of the proposed device is about ten times that of a conventional brain scanner. The scatter fraction is greater, but the scattered radiation has a very flat distribution. By designing the device to fit in an existing mammography unit, conventional mammograms can be taken after the injection of the radio-pharmaceutical allowing exact registration of the emission and conventional mammographic images.

The C15O2 build-up technique to measure regional cerebral blood flow and volume of distribution of water

A new method to measure regional CBF (rCBF) and volume of distribution of water is presented. It centres on recording the tissue build-up and retention of 15O-labelled water during the continuous inhalation of 15O-labelled carbon dioxide. Simultaneously, the arterial concentration is continuously monitored, and corrections for delay and dispersion in the recorded response are made by curve fitting. The values for the volume of distribution of water obtained in four normal subjects were close to reported in vitro values. Using the same fixed distribution volumes for both build-up and steady-state studies resulted in comparable rCBF values for both techniques.

Validation of PET-acquired input functions for cardiac studies

To validate the determination of the arterial input function by noninvasive dynamic PET imaging, measurements of blood-pool activity in canine LV by PET were compared to beta probe measurements of arterial blood withdrawn directly from the LV. PET scans were done during intravenous bolus injections of [13N]ammonia or 82Rb, while the activity of blood withdrawn continuously from a catheter inserted in the LV was measured with a beta probe. PET determinations of LV blood-pool activity were compared with dispersion-corrected beta probe time-activity curves. In 15 experiments involving four dogs under a wide range of physiologic conditions, LV time-activity curves obtained with PET matched well in shape with those obtained with the beta probe. Linear regression yielded slopes within 10% of unity (95% confidence interval) and high correlation (r greater than 0.968, p less than 0.001). We conclude that noninvasive measurement of the arterial input function by dynamic PET imaging is valid.