Role of advanced magnetic resonance imaging in the assessment of malignancies of the mediastinum

Table 1 Diffusion weighted derived parameters of different model analysis

Mono-exponential model
ADC	Apparent diffusion coefficient	Exponential signal decay of water molecules in a voxel by voxel basis.
IVIM-derived parameters
D	True diffusion of H2O molecules	Not influenced by movement of water molecules within capillaries
f	Perfusion contribution to diffusion signal	Fractional volume of flowing water molecules within capillaries
D	Perfusion contribution to diffusion signal decay	Amount of non-diffusional random movements of water molecules
DKI-derived parameters
Dapp	Apparent diffusion	Estimation of diffusion coefficient in the direction parallel to the orientation of diffusion sensitizing agents
Kapp	Apparent diffusional kurtosis	Measures the deviation of the true diffusion from a Gaussian pattern.
DTI-derived parameters
MD	Mean diffusivity	Reflects the average diffusion of water molecules in all three directions.
FA	Fractional anisotropy	Measures the extent to which diffusion is non-uniform in the three orthogonal directions.

ADC: Apparent diffusion coefficient; IVIM: Intravoxel incoherent motion; MD: Mean diffusivity; FA: Fractional anisotropy.

Table 2 Perfusion weighted imaging derived parameters

Semiquantitative parameters
Initial area under the curve	Include information of blood flow, blood volume, permeability, extravascular–extracellular space volume and microvessel density.
Time to peak	Depends on tissue perfusion
Wash in	Represents velocity of enhancement
Wash out	Represents velocity of enhancement loss
Quantitative parameters
Ktrans	Influx volume transfer constant of a contrast agent from the vascular compartment to the interstitial space
Ve	Volume of extravascular–extracellular space per unit of tumor volume
Vp	Blood plasma volume
Kep	Rate constant between extravascular-extracelular space and plasma

Table 3 Masaoka–Koga staging system

Stage	Degree of invasion	5 yr survival rate (%)
I	Tumor completely encapsulated	96-100
IIa	Microscopic tumor invasion into the capsule	86-95
IIb	Tumor invasion into the surrounding fat
III	Tumor invasion into surrounding organ such as the pericardium, great vessel or lung	56-69
IVa	Pleural or pericardial dissemination	11-50
IVb	Lymphatic or hematogeneous metastasis

Table 4 The tumor node metastasis staging system by International Thymic Malignancy Interest Group

		TNM staging
Tumor (T) descriptor		I	II	IIIA	IIIB	IVA	IVB
T1a	Encapsulated or unencapsulated tumor, with or without extension into fat	X				X	X
T1b	Invasion of mediastinal pleura	X				X	X
T2	Invasion of pericardium		X			X	X
T3	Involvement of lung, chest wall, phrenic nerve, brachiocephalic vein, superior vena cava, or hilar (extrapericardial) pulmonary vessels			X		X	X
T4	Invasion of thoracic aorta, arch vessels, main pulmonary artery, trachea, esophagus, or myocardium				X	X	X
Node (N) descriptor		I	II	IIIA	IIIB	IVA	IVB
N0	No lymph node metastasis	X	X	X	X	X	X
N1	Involvement of anterior (perithymic) lymph nodes					X	X
N2	Involvement of deep intrathoracic or cervical lymph nodes						X
Metastasis (M) descriptor		I	II	IIIA	IIIB	IVA	IVB
M0	No Metastasis	X	X	X	X	X (N1)	X (N2)
M1a	Pleural or pericardial metastatic nodule or lesions					X (N0,1)	X (N2)
M1b	Pulmonary intraparenchymal metastastic nodule or distant organ metastasis						X (any T, N)

TNM: Tumor node metastasis staging system; ITMIG: International Thymic Malignancy Interest Group.

Table 5 Treatment monitoring and recurrence behavior

	Good response	Poor response
T2WI	No tumor ↑ SI in bone marrow	Residual/↑soft tissue mass ↑ extent bone marrow invasion
DWI	↑ ADC	↓ ADC
DCE-MRI	↓ slope/absent enhancement	Persistent / ↑ enhancement
MRS	↑ Choline peak	↓ Choline peak

T2WI: T2 weighted imaging; SI: Signal intensity; DWI: Diffusion weighted imaging; ADC: Apparent diffusion coefficient; DCE-MRI: Dynamic contrast enhanced magnetic resonance imaging; MRS: Magnetic resonance spectroscopy. Modified from Vilanova et al[18].