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Imaging Characteristics
	Method		Contrast	Cost		Contraindications	Example indication		Bedside
X-ray	High energy radiation waves	Two dimension	Barium fluoroscopy	$	Density	None	Fracture, CXR	Limited discrimination of tissues	Yes
CT	Combines x-ray and computer	Axial	IV iodine Contrast	$$$	Density Hounsfield numbers	Iodine allergy / renal function	Sinusitis, Trauma	Tissue discrimination	No
MRI	Strong magnet, radio waves and computer	Axial, sagittal, coronal	Gadolinium Sequences	$$$$	Intensity	Magnetic objects	Brain tumor, Knee joint injury	SuperbTissue discrimination	No
Ultrasound	High frequency sound waves/ computer / real time image		------	$$	Echo	Gas / Bone relatively	Ectopic pregnancy, Deep vein thrombosis	Doppler can detect flow	Yes
Nuclear Medicine	Radioactive substance administered inside body	Gamma camera	------	$$$	Activity	Child bearing age and children	Parathyroid adenoma, Bone scan	Function	No
Contrast Filling Lumens	Vessels, bowel, uterus	X-ray	Iodine or barium	$$$	Density	Iodine allergy and renal function	Lower GI, Carotid angiogram	Inner wall and lumen	No

Appearance of Tissues in Various Imaging Modalities
	Terms	Acute Extravascular Blood	Air	Fat	Fluid / CSF	Bone
Plain Films	Density	Gray	Dark	Gray	White	White
CT	Density	Hyperdense / Bright	Hypodense / Dark	Hypodense / Dark	Hypodense / Dark	Hyperdense / Bright
	Hounsfield Units	50-80 H.U Acute blood	-1000 H.U	-10-100 H.U	0 H.U	+1000 H.U
MRI T1 Wtd Image	Intensity	Hypointense / Dark	Hypointense / Dark	Hyperintense / Bright	Hypointense / Dark	Hypointense / Dark
MRI T2 Wtd Image	Intensity	Hypointense / Dark	Hypointense / Dark	Isointense/ Gray	Hyperintense / Bright	Hypointense / Dark
Ultrasound	Echo	Hyperechoic/ Bright	Echogenic / Does not transmit	Echogenic	Anechoic	Hyperechoic / Does not transmit / shadowing

Appearance of Tissues in Various Imaging Modalities
	Plain X-ray	CT	T1 MRI	T2 MRI	Ultrasound
	Density	Density	Intensity	Intensity	Echo
Air	Dark	Hypodense / Dark	Hypointense / Dark	Dark	Hyperechoic
Fat	Gray	Hypodense / Dark	Hyperintense / Bright	Isointense / Gray	Echogenic with shadowing
Clear Fluid	White	Hypodense / Dark gray	Hypointense / Dark	Hyperintense / Bright	Anechoic with posterior enhancement
Tissue / Organs	White	Hyperdense / Gray	Gray	Hypointense Dark gray	Isoechoic
Bone / Calcification	Dense white	Hyperdense / Dense white	Hypointense / Dark	Hypointense / Dark gray	Hyperechoic with shadowing

Tissue appear similarly in plain x-ray and CT.

Hounsfield units apply to CT.

Air -1000 H.U, Fat -10-100 H.U, Clear fluid 0 H.U, Bone + 1000 H.U

Hounsfield Units: Increasing densities representing tissues

Air is dark and bone is bright, with the rest of the tissues in between (shades of gray) in appearance in that order.