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  • Title: Pulse repetition time and contrast enhancement: simulation study of Gd-BOPTA and conventional contrast agent at different field strengths.
    Author: Yrjänä SK, Vaara T, Karttunen A, Koivukangas J.
    Journal: Invest Radiol; 2008 Apr; 43(4):267-75. PubMed ID: 18340251.
    Abstract:
    OBJECTIVES: To investigate theoretically enhancement and optimal pulse repetition times for Gd-BOPTA and Gd-DTPA enhanced brain imaging at 0.23, 1.5, and 3.0 T. METHODS: The theoretical relaxation times of unenhanced, conventional contrast agent (Gd-DTPA) and new generation contrast agent (Gd-BOPTA) enhanced glioma were calculated. Then, simulation of the signals and contrasts as a function of concentration and pulse repetition time (TR) in spin echo sequence was done at 0.23, 1.5, and 3.0 T. The effect of echo time (TE) on tumor-white matter contrast was also clarified. Three patient cases were imaged at 0.23 T as a test of principle. RESULTS: Gd-BOPTA may give substantially better glioma-to-white matter contrast than Gd-DTPA but is more sensitive to the length of TR. These characteristics are accentuated at 0.23 T. Optimal TR lengths are shorter for Gd-BOPTA than for Gd-DTPA enhanced imaging at all field strengths. TR optimized for Gd-DTPA may thus give suboptimal contrast in Gd-BOPTA enhanced imaging. Higher enhancement with Gd-BOPTA is further accentuated by short TE. CONCLUSION: Appropriate TRs at 0.23 T appear to be approximately 300 to 400 milliseconds and 250 to 300 milliseconds, at 1.5 T 500 to 600 milliseconds and 400 to 450 milliseconds and at 3.0 T 550 to 650 milliseconds and 475 to 525 milliseconds using Gd-DTPA and Gd-BOPTA, respectively. For Gd-BOPTA enhanced imaging, it seems justified to optimize TR according to contrast and seek options like parallel excitation (Hadamard encoding) for increasing the number of slices and SNR.
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