Purpose: The water molecule exchange rates in a series of DyDOTA‐(amide)_X chelates were fine‐tuned to maximize the effects of T₂‐exchange line broadening and improve T₂ contrast.Methods: Four DyDOTA‐(amide)_X chelates having a variable number of glycinate side‐arms were prepared and characterized as T₂‐exchange agents. The nonexchanging DyTETA chelate was also used to measure the bulk water T₂ reduction due solely to T₂*. The total transverse relaxivity (r_2tot) at 22, 37, and 52°C for each chelate was measured in vitro at 9.4 Tesla (400 MHz) by fitting plots of total T₂⁻¹ versus concentration. The water molecule exchange rates for each complex were measured by fitting ¹⁷O line‐width versus temperature data taken at 9.4 Tesla (54.3 MHz).Results: The measured transverse relaxivities due to water molecule exchange (r_2ex) and bound water lifetimes (τ_M) were in excellent agreement with Swift‐Connick theory, with DyDOTA‐(gly)₃ giving the largest r_2ex = 11.8 s⁻¹ mM⁻¹ at 37°C.Conclusion: By fine‐tuning the water molecule exchange rate at 37°C, the transverse relaxivity has been increased by 2 to 30 times compared with previously studied Dy³⁺‐based chelates. Polymerization or dendrimerization of the optimal chelate could yield a highly sensitive, molecule‐sized T₂ contrast agent for improved molecular imaging applications. Magn Reson Med 71:1179–1185, 2014. © 2014 Wiley Periodicals, Inc.

Isoattenuating gallstones can be differentiated from bile by using dual-layer spectral CT and two-dimensional histograms of Compton and photoelectric attenuation; this method improved gallstone det... BackgroundPreviously reported dual-energy CT methods for detecting noncalcified gallstones have reduced accuracy for gallstones smaller than 9 mm.PurposeTo develop a dual-energy CT method for diffe...

The electron-multiplying charge-coupled device (EMCCD) offers improved quantum efficiencies (40 to 95%) over a broader range of wavelengths (400 to 900 nm) and a higher intrinsic resolution (<100 mum using photon counting) when compared to photomultiplier tubes. The electron gain achieved in the multiplication register of an EMCCD effectively reduces the readout noise to less than 1 electron/pixel, making them sensitive to single photoelectrons. Our prototype camera uses the Texas Instruments Impactrontrade EMCCD model TC253SPD-B0 (7.4 mum square pixels) which is cooled under vacuum to -50degC using a four stage Peltier and liquid heat exchanger. Shuttered lens-coupling is used to image the optical light from a 3 mm thick monolithic CsI(Tl) crystal. Precise clocking for the EMCCD is provided by a National Instruments FPGA controller (PCI-7811R) and LabVIEW FPGA module (version 8.0). A custom built electronics box contains the clock driver circuitry and 16-bit video board for digital conversion of the video signal. Our optical coupling method differs from other EMCCD SPECT systems by using lenses rather than fiber optic bundles for transfer. TC253 characterization tests measured a maximum gain just over 1000times, dark current rate of 0.14 e/p/s, read noise of 18.2 e/p, and spurious charge generation of 4 e/p. A light integration intrinsic resolution of 110 mum FWHM was measured. Light integration images of a line phantom using a single pinhole collimator were used for SPECT reconstruction. We found the relative high spurious charge generation and low quantum efficiency of the TC253 made it incapable of photon counting for low energy sources using lens coupling.

Bioluminescent imaging (BLI) of cells expressing luciferase is a valuable noninvasive technique for investigating molecular events and tumor dynamics in the living animal. Current usage is often limited to planar imaging, but tomographic imaging can enhance the usefulness of this technique in quantitative biomedical studies by allowing accurate determination of tumor size and attribution of the emitted light to a specific organ or tissue. Bioluminescence tomography based on a single camera with source rotation or mirrors to provide additional views has previously been reported. We report here in vivo studies using a novel approach with multiple rotating cameras that, when combined with image reconstruction software, provides the desired representation of point source metastases and other small lesions. Comparison with MRI validated the ability to detect lung tumor colonization in mouse lung.