Apparent diffusion coefficient (ADC)

Measures the magnitude of diffusion (of water molecules) within tissue ¹⁾.

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.

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 (ROIs) 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.

see Apparent diffusion coefficient in glioma.

see Apparent diffusion coefficient in medulloblastoma.

see Apparent diffusion coefficient in metastases.

see Apparent diffusion coefficient in meningioma.

see Apparent diffusion coefficient in Hydrocephalus.

see Apparent diffusion coefficient in vestibular schwannoma.