Table 1.

A list of the advantages and disadvantages of the techniques

Type	Technique (s)	Advantages	Disadvantages
Gas exchange	O2/CO2 analysis	Small risk to subjects Simple to implement Equipment requirements modest Inexpensive	No regional information Limited accuracy
	Intrabreath R Shunt Bohr Fowler dead space	Noninvasive Minimal risk to subjects Relatively simple to implement Equipment requirements moderate Inexpensive to make measurements if equipment is available	No regional information Limited accuracy
	MIGET	Quantitative Well established Allows estimate of diffusion limitation Relatively inexpensive to make measurements if equipment is available	Invasive Technically demanding No regional information ${\dot{V}}_{\text{A}}/\dot{Q}$ inequality express as individual distributions of ${\dot{V}}_{\text{A}}$ and $\dot{Q}$ to ${\dot{V}}_{\text{A}}/\dot{Q}$ ratio
Imaging	SPECT	Minimally invasive Low risk to subjects Repeated measures possible Regional information Relatively inexpensive compared to other imaging techniques	Exposure to ionizing radiation Semiquantitative as usually implemented Relatively low resolution compared to other imaging techniques Repeated measures possible but must be spaced to clear tracer Data acquisition can be time consuming
	PET	Quantitative High resolution Some validation studies performed	Exposure to ionizing radiation Repeated measures possible but must be spaced to clear tracer Relatively expensive Limited lung field analysis Any ventilation distal to vascular obstruction is not evaluated because tracer is not delivered Limited postures possible
	MRI	Noninvasive Minimal risk with adequate screening No exposure to ionizing radiation Resolution relatively high to high depending on technique Repeated measures possible Regional information Quantitative Validation studies for some techniques	Technically demanding Expensive Some techniques time consuming Potential allergic reactions to contrast, if used Limited availability especially for SF6 and hyperpolarized gas imaging Limited postures possible
	CT	High resolution Regional information Less expensive than some other imaging techniques Can be quantitative	Exposure to ionizing radiation Potential contrast reaction Repeated measures in humans limited by radiation exposure Limited validation Limited postures possible
	EIT	Inexpensive Portable Temporal information No ionizing radiation Minimal risk Repeated measures possible Minimal to no patient input required Modest validity Multiple postures possible Regional Information	Unclear and nonuniform spatial resolution Low resolution Reconstruction of image is complex Image is dominated by information close to electrodes Small field of view not suitable for some patients (e.g. pacemaker)
Microspheres	Fluorescent or radioactive	Relatively high resolution Quantitative Repeated measures possible Regional information Validation studies show reasonable validity	Destructive technique (tissue obtained post mortem) Distortion of tissue ex vivo may affect results