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ABSTRACT: A variety of shortcomings are associated with most currently used gastrointestinal contrast agents for magnetic resonance imaging (MRI). Artifacts resulting from peristalsis and other motions in the abdominal region are produced by many positive contrast agents (which increase signal intensity). Although this is not a problem for negative contrast agents (which decrease signal intensity), some negative contrast agents produce magnetic susceptibility artifacts that are especially pronounced at high field strength and with gradient echo pulse sequences. These susceptibility artifacts are produced by both paramagnetic and diamagnetic agents. It has been demonstrated in phantoms, however, that susceptibility matching can be used to produce contrast agents with desirable relaxation and contrast properties but without deleterious susceptibility artifacts. We now report results of animal tests of such an oral contrast agent, consisting of a suspension of superparamagnetic iron oxide particles and diamagnetic barium sulfate particles, compared to individual suspensions of the iron oxide and of the barium sulfate. Iron oxide was the least effective and the matched susceptibility mixture was the most effective for the intestine, which has traditionally been the most difficult region of the GI tract to visualize clearly. Matched susceptibility mixtures, which are inherently able to yield images free of susceptibility artifacts without compromising contrast, show promise of being improved oral negative contrast agents for use in gastrointestinal MRI.
Magnetic Resonance Imaging 02/1997; 15(5):559-66. · 1.99 Impact Factor
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ABSTRACT: A family of new on-resonance saturation pulses for magnetization transfer in MRI is proposed. These pulses can be represented as a product of a shaped function and a cosine function. The shaped function can have many different forms, one of which is a Gaussian function. The experimental results on a 1.0 T whole body scanner show that the new on-resonance pulses are more efficient for magnetization transfer than either on-resonance binomial sequence pulses or off-resonance Gaussian pulses at the same power level.
Magnetic Resonance in Medicine 10/1996; 36(3):481-6. · 2.96 Impact Factor
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J R Ballinger
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ABSTRACT: Radiologic procedures are extremely valuable in the diagnostic work-up of many cancers but are limited for screening purposes to a few diseases. Radiologists have developed an extensive armamentarium of tools, from plain radiographs and nuclear-medicine scans to ultrasound, computed tomography, magnetic resonance imaging, positron emission tomography, and single-photon emission computed tomography. This article includes suggested protocols for working up the most common cancers.
Medical Clinics of North America 02/1996; 80(1):201-18. · 2.47 Impact Factor
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ABSTRACT: Strong fat signal in regions where a large susceptibility difference exists, for instance at the interface between air and tissue near the maxillary sinus, may not be eliminated by currently available fat suppression techniques without sacrificing the overall quality of the images. In this article, we show that this fat signal, which appears as a susceptibility artifact, can be significantly reduced by using an optimized presaturation pulse with sharp edges and a broad bandwidth, while causing minimal disturbance of the water signal. Several optimized presaturation pulses can be reproduced by the Fourier coefficients provided in the Appendix.
Magnetic Resonance in Medicine 05/1995; 33(4):582-7. · 2.96 Impact Factor
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ABSTRACT: To determine if changes in PCr/Pi and PME can be used to predict lack of tumor response to chemotherapy in a murine model of a chemotherapy-resistant human osteosarcoma.
Cisplatin-resistant sublines were grown from high-grade cisplatin-sensitive human osteosarcoma. Surface coil localized 31P NMR spectroscopy of implanted cisplatin-resistant and sensitive osteosarcoma tumors in nude mice was performed.
A cisplatin-resistant subline of a sensitive human osteosarcoma was developed that was five times more resistant to cisplatin than the parent cell line. Our NMR data shows a statistically significant difference in the change in the PCr/Pi ratio after treatment between sensitive and resistant osteosarcomas at the alpha = 0.05 level. Changes in PME were seen in the sensitive tumors but were not statistically significant.
Changes in PCr/Pi predict lack of tumor treatment response in human osteosarcoma implanted into nude mice with a specificity of 70% and a sensitivity of 54%. Monitoring of PCr/Pi in human osteosarcoma patients may allow detection of response to chemotherapy before conventional imaging techniques.
Magnetic Resonance Imaging 02/1995; 13(6):877-83. · 1.99 Impact Factor
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ABSTRACT: Our objective was to determine whether changes in PME and PCr/Pi can be used to predict lack of tumor response to chemotherapy in a murine model of human osteosarcoma. A chemotherapy-sensitive human osteosarcoma cell line was implanted into the flank of 22 nude mice. Cisplatin was administered to 11 of the mice 9 days postimplantation. 31P MR spectroscopy was performed pre- and post-chemotherapy in both sets of mice. Statistically significant changes in PCr/Pi occur from post-chemotherapy in the treated mice, but not in the untreated mice during the same time. Change in PME parallels changes in tumor volume. Changes in PCr/Pi predict lack of chemotherapy treatment in human osteosarcoma implanted into nude mice with a specificity of 80% and a sensitivity of 63%. The change in PCr/Pi occurs prior to any changes in volume of the tumor [corrected].
Magnetic Resonance Imaging 02/1994; 12(6):935-43. · 1.99 Impact Factor
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ABSTRACT: The combination of diamagnetic barium sulfate and superparamagnetic iron oxide (SPIO) in one suspension produces a macroscopic cancellation of positive and negative magnetic susceptibility components that can potentially eliminate susceptibility artifacts even with gradient echo pulse sequences. The relaxation properties that make the SPIO suspension a useful negative contrast agent are retained.
Magnetic Resonance in Medicine 12/1993; 30(5):646-9. · 2.96 Impact Factor
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ABSTRACT: The individual components of two commercially available barium sulfate (BaSO4) suspensions, Liquid HD and E-Z-paque (E-Z-EM Inc., Westbury, NY), were investigated to determine their contribution to relaxation. Longitudinal and transverse relaxation times of suspensions and solutions of the different BaSO4 particles and the vehicle used to keep them in suspension were measured separately at 2.0 T. A multiple echo Carr-Purcell-Meiboom-Gill (CPMG) pulse sequence was used for T2 determinations with different values of the echo spacing 2 tau. Longer values of 2 tau resulted in significant shortening of the calculated T2 relaxation times, indicating that the major mechanism leading to signal loss in BaSO4 suspensions is the diffusion of water molecules through susceptibility gradients in the vicinity of suspended particles. At higher BaSO4 concentrations, decreased water proton density also produces significant signal loss. Viscosity has little effect on the relaxation. A combination of larger and smaller BaSO4 particle sizes was found to be more effective than smaller sizes only in enhancing signal decay.
Magnetic Resonance Imaging 02/1993; 11(5):635-44. · 1.99 Impact Factor
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ABSTRACT: In this in vitro study of a potential oral MRI contrast agent, barium sulfate suspension (BSS), the object was to examine the effect of varying barium sulfate concentration on signal intensity while keeping suspension additives the same; and to optimize the concentration of a specific preparation of BSS. A phantom was used to test suspensions with concentrations of barium sulfate ranging from 90% to 220% w/v. T1-weighted, T2-weighted, and gradient echo sequences all showed a decrease in signal as concentration was increased to 170%. Between 170% and 220%, the signal intensity was constant on the T1-weighted and T2-weighted sequences. With the proton density and gradient echo sequences, there was a slower rate of decline in the signal intensity in the 170 to 220% range of BSS concentrations. We conclude that BSS with a concentration in the range of 170% to 220% w/v is optimum for the specific preparation used. We speculate that the behavior of the signal-to-noise ratio with changing concentration is explained by factors including proton density, T1 relaxation enhancement, diffusion effects, and magnetic field inhomogeneity, depending on the particular pulse sequence used.
Magnetic Resonance Imaging 02/1992; 10(4):637-40. · 1.99 Impact Factor
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ABSTRACT: Objective: To determine if changes in and PME can be used to predict lack of tumor response to chemotherapy in a murine model of a chemotherapy-resistant human osteosarcoma. Material and Methods: Cisplatin-resistant sublines were grown from high-grade cisplatin-sensitive human osteosarcoma. Surface coil localized 31P NMR spectroscopy of implanted cisplatin-resistant and sensitive osteosarcoma tumors in nude mice was performed. Results: A cisplatin-resistant subline of a sensitive human osteosarcoma was developed that was five times more resistant to cisplatin than the parent cell line. Our NMR data shows a statistically significant difference in the change in the ratio after treatment between sensitive and resistant osteosarcomas at the α = 0.05 level. Changes in PME were seen in the sensitive tumors but were not statistically significant. Conclusions: Changes in predict lack of tumor treatment response in human osteosarcoma implanted into nude mice with a specificity of 70% and a sensitivity of 54%. Monitoring of in human osteosarcoma patients may allow detection of response to chemotherapy before conventional imaging techniques.
Magnetic Resonance Imaging.
