Читать книгу Salivary Gland Pathology - Группа авторов - Страница 64

Proton density images are obtained with a long tr but short te, resulting in an image with less tissue contrast but high signal‐to‐noise ratio. These are uncommonly used in the head and neck.

Table 2.2. Tissue characteristics on T1 and T2 MRI.^a

	T1	T2
Increased signal	FatCalciumbProteinaceous fluid (high)cSlow flowing bloodMelaninHyperacute hemorrhaged (oxyhemoglobin)Subacute hemorrhage (intracellular and extracellular methemoglobin)Gadolinium contrastManganeseCholesterol	Water (CSF) or edemaProteinaceous fluidHyperacute hemorrhage (oxyhemoglobin)Subacute hemorrhage (extracellular methemoglobin)Slow flowing bloodFat (FSE T2 scans)
Intermediate signal	Hyperacute hemorrhage (oxyhemoglobin)Acute hemorrhage (deoxyhemoglobin)CalciumbGray matterWhite matter (brighter than gray matter)Soft tissue (muscle)Proteinaceous fluidc	Grey matter (brighter than white matter)White matterProteinaceous fluidcCalciumb
Decreased signal	Water (CSF) or edemaFast flowing bloodCalciumbSoft tissueAcute hemorrhage (deoxyhemoglobin)Chronic hemorrhage (hemosiderin)CalcificationAirSimple cyst (low protein)	CalciumbMelaninHemosiderinFlowing bloodhemorrhagic cystIron depositionAcute hemorrhage (deoxyhemoglobin)Early subacute hemorrhage (intracellular methemoglobin)Chronic hemorrhage (hemosiderin)AirFast flowFat (conventional or non‐FSE T2 scan)

^a MRI signal on T1 and T2 predominantly from intracranial exam at 1.5T (Tesla).

^b Signal from calcium deposition is complex. Calcium concentrations of under 30% by weight have high T1 signal and intermediate T2 signal, but over 40% have decreasing signal on T1 and T2. The surface area of the calcium particle also has an effect, with large surface area resulting in increased T1 signal (Henkelman et al. 1991).

^c Depends on the protein concentration (complex cysts, abscess).

^d MRI signal of intracranial hemorrhage is quite complex and dependent on multiple factors with degrees of variability.

CSF = cerebrospinal fluid.