Furthermore, the drift itself is small, so measurements will be influenced by noise and likely difficult to reliably estimate for correction of an individual patient’s data set. Therefore, scanner drift may introduce tissue-dependent systematic deviations in signal enhancement profiles, Quizartinib nmr which, on our system, are particularly noticeable for higher T10 values, such as those found in CSF. It is possible that

CSF flow influences the in vivo measurements, but at present we do not have an explanation for the differential drift observed in phantoms. Converting signal enhancement profiles to contrast agent concentration noticeably altered the relationships between the different tissues for both subject groups. This arises due to the difference in T10 values between tissues and the nonlinear relationship between enhancement and concentration given by Eq. ( 2) and clearly illustrated in Fig. 2 of http://www.selleckchem.com/products/17-AAG(Geldanamycin).html Schabel and Parker [19]. These results demonstrate that it is dangerous to assume that signal enhancement consistently relates to the amount of contrast agent present in any given tissue, compared to others, when those tissues differ in their intrinsic parameters T10 or r1. This emphasizes the importance of selecting an appropriate control group, with a view to

minimizing these differences. Similarly, comparing the same tissue in a normal state and differing degrees of disease will not be consistently represented by signal enhancement, if T10 or r1 is altered during the disease process. Thus, a change in T10 or r1 either as part of, or associated with, the disease process can affect the changes observed in signal enhancement. For example, in addition to increased leakage of contrast agent, a common consequence of BBB breakdown is an increase in tissue water content. This elevated water content will lead to local changes in T10 and r1 that alter the observed signal enhancement, in addition to the change resulting from increased contrast agent concentration. Previous work suggests that T10 would be elevated in tissue

with greater water content, not while r1 is related to tissue solids content and reduces in tissue with greater water content [32] and [33]. The enhancement–concentration relationship defined by Eq. ( 2) indicates that these would produce opposing effects, with increased T10 leading to greater signal enhancement and reduced r1 leading to lower signal enhancement in tissue with greater water content. Therefore, when signal enhancement is interpreted, it is not possible to know whether enhancement differences are due to a true difference in contrast agent concentration or to differences in T10 and/or r1. Using a model, such as that proposed in Eq. ( 2), to calculate contrast agent concentration attempts to overcome these limitations, provided that T10 and r1 can be reliably estimated for all tissues.