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pattern, making its more detailed explanation worthwhile as a model for understanding the principles of MR signal characteristics (Table 2.3). These are affected by many factors both intrinsic to the hemorrhage and related to MR scanning. Operator-dependent factors include strength of magnet, pulse sequence (e.g. SE, GE, EPI, etc.) and parameters set, such as the repetition time (TR) and the echo time (TE). Intrinsic factors are multifactorial but the hemoglobin oxidation state and red cell morphology are the most important.

Parenchymal Hematomas

Hyperacute Stage

Within minutes of the hemorrhage, intact red cells will contain oxyhemoglobin and there will be protein-rich serum and platelets. The appearances are non-specific and virtually indistinguishable from any brain lesion that causes increased water content of the brain, i.e. white on T2 and gray/black on T1.

Acute Stage

Within the first few hours, deoxyhemoglobin is formed, which is paramagnetic. This particularly affects the T2 relaxation, resulting in marked reduction in signal (black) on T2 weighting, but has little effect on T1. The low signal is accentuated on GE sequences because of the susceptibility effect.

Subacute Stage

After several days, methemoglobin forms, which is initially intracellular and gives rise to high signal on T1 weighting but remains low on T2. As the cells hemolyze, extracellular methe-moglobin accumulates in the hematoma, which

Cure Your Yeast Infection For Good

Cure Your Yeast Infection For Good

The term vaginitis is one that is applied to any inflammation or infection of the vagina, and there are many different conditions that are categorized together under this ‘broad’ heading, including bacterial vaginosis, trichomoniasis and non-infectious vaginitis.

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