====== Apparent diffusion coefficient (ADC) ======

{{ ::apparent_diffusion_coefficient.jpg?400|}}
Measures the magnitude of [[diffusion]] (of [[water molecule]]s) within [[tissue]]
((Sener RN. Diffusion MRI: apparent diffusion coefficient (ADC) values in the normal brain and a classification of brain disorders based on ADC values. Comput Med Imaging Graph. 2001;25 (4): 299-326.)).

It is commonly clinically calculated using [[MRI]] with [[diffusion weighted imaging]] ([[DWI]]).

DWI exploits the random motion of water molecules. The extent of tissue cellularity and the presence of intact cell membrane help determine the [[impedance]] of water molecule diffusion. This impedance of water molecules diffusion can be quantitatively assessed using the apparent diffusion coefficient (ADC) value. 

===== Measurement =====

ADC values are calculated automatically by the software and then displayed as a [[parametric mapping]] that reflects the degree of diffusion of water molecules through different tissues. Then, by use of a dedicated workstation, ADC measurements are recorded for a given region by drawing regions of interest ([[ROI]]s) on the ADC map.

An ADC of a tissue is expressed in units of mm2/s. There is no unanimity regarding the boundaries of the range of normal diffusion, but ADC values less than 1.0 to 1.1 x  10-3 mm2/s (or 1000-1100 x 10-6 mm2/s) are generally acknowledged in adults as indicating restriction. However, this is entirely dependent on the organ being imaged and the pathology.

Some rough useful values (10-6 mm2/s) 8-10:

white matter: 670-800

cortical grey matter: 800-1000

deep grey matter: 700-850 

CSF: 3000-3400

astrocytoma

Gd II: 1273 ± 293

Gd III: 1067 ± 276

Gd IV: 745 ± 135

Diffusion changes are correlated to the clinical deficit and are potentially useful for early diagnosis and longitudinal evaluation, especially in the context of pharmacological trials.

===== Apparent diffusion coefficient in glioma =====

see [[Apparent diffusion coefficient in glioma]].

===== Apparent diffusion coefficient in medulloblastoma =====

see [[Apparent diffusion coefficient in medulloblastoma]].

===== Apparent diffusion coefficient in metastases =====

see [[Apparent diffusion coefficient in metastases]].

===== Apparent diffusion coefficient in meningioma =====

see [[Apparent diffusion coefficient in meningioma]].

===== Apparent diffusion coefficient in hydrocephalus =====

see [[Apparent diffusion coefficient in Hydrocephalus]].

===== Apparent diffusion coefficient in vestibular schwannoma =====

see [[Apparent diffusion coefficient in vestibular schwannoma]].