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The choice of pulse-sequence parameters (TE, flip angle) and contrast agent dose (administration of preload), which impact the accuracy of rCBV estimation, 9, 10 also has implications for PSR estimates, and understanding this relationship is important for properly selecting PSR imaging parameters, interpreting PSR results, and comparing values across tumor types and imaging centers.Īll studies were performed at 1.5T (CVi GE Healthcare, Milwaukee, Wisconsin) with commercial gradients and phased-array radio-frequency coils. However, with reduced T1 weighting, increased T2* weighting, and increased contrast agent dose, T2* effects can dominate, with substantially smaller PSR.
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Specifically, at low contrast agent doses, postbolus signal can be dominated by T1 shortening in the intravascular (normal brain) and/or extravascular extracellular space (tumor) when a T1-weighted pulse sequence is used, yielding relatively high PSR. We hypothesized that PSR depends, in part, on the T1 weighting of the pulse sequence and the total dose of administered contrast agent, including preload. In this study, we aimed to determine how TE, flip angle, and contrast agent dose in DSC-MR imaging impact PSR and to explain why there may be discrepancies in reported PSR values for similar tumors. 12 An understanding of the dependence of postbolus signal on these nonphysiologic factors is important for designing protocols that accentuate physiology-dependent differences in PSR and for interpreting PSR results in the clinical setting.
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For instance, elevated postbolus relaxivity is observed following second contrast agent injections in normal brain 11 and brain tumors having BBB disruption, especially following preload administration that diminishes T1 leakage effects. Although PSR studies have typically used single-dose contrast without preload, PSR may be evaluated with rCBV, for which higher contrast dose and preload administration for reducing T1 leakage contamination are beneficial 9, 10 the dependence of PSR on contrast dose and preload is therefore important. A spectrum of pulse-sequence parameters with low (long TE 3), intermediate (low flip angle, intermediate TE 2, 4, 5 and high flip angle, intermediate TE 1, 7), and high (high flip angle, short TE 6) T1 weighting have been published for quantifying PSR, with some conflicting inconsistent results. 5 ⇓ ⇓– 8Īlthough PSR has promise for elucidating tumor biology, its etiology is poorly characterized and likely the complex multifactorial interplay of technical (contrast dose, DSC-MR imaging pulse sequence) and pathophysiologic (vascular permeability, tumor cell volume fraction) factors. The variable return of the postbolus signal to the prebolus baseline has been termed “percentage signal recovery” and was proposed as a tool for differentiating nonenhancing gliomas and non-neoplastic lesions 1 progressive metastatic disease from radiation injury after stereotactic radiosurgery 2, 3 recurrent GBM from radiation necrosis 4 and common intra-axial brain neoplasms such as metastasis, high-grade glioma, and lymphoma. However, postbolus signal depression or elevation is frequently observed and represents failure of the signal-time curve, S(t), and the corresponding relaxivity-time curve, ΔR2*(t), to return to the prebolus baseline as expected in idealized tracer kinetics. ABBREVIATIONS: DSC dynamic susceptibility contrast GBM glioblastoma multiforme PSR percentage signal recovery rCBV relative cerebral blood volumeįirst-pass transient signal loss is the fundamental feature of DSC-MR imaging signal-time curves and the principal determinant of rCBV estimates.