Table 1.

Main characteristics of available techniques to evaluate morphological and functional microvascular damage.

Technique	Principle	Skills	Disadvantages	Linked Organ Damage
Laser speckle contrast analysis (LASCA) and imaging (LSCI)	When the laser light illuminates the tissue, the static areas result in a stationary speckled pattern, which fluctuates due to the movement of the red blood cells, causing them to appear blurred and thus creating an overall speckled pattern. Based on the level of blurring (contrast), the degree of blood perfusion is determined (low contrast = high perfusion).	-Fast data acquisition -Good spatial resolution (images rich in detail) -Possibility of both spatial (areas) and temporal (dynamic response) evaluations -Non-contact technique -Valid instrument in subjects of Black ethnicity -Decreased PBP at the fingertips, periungual, palmar aspect of third finger and palm areas in SSc patients -After cold test, SSc patients had a significant reduction in blood flow and a higher recovery time compared to HS and PRP -Increase in PBP during long-term therapy with the endothelin receptor antagonist bosentan (BOSE) and the synthetic analog of prostacyclin PGI2 iloprost (ILO) in a 4-years follow up in patients with Sac	Measures perfusion at tissue and skin structure levels (capillaries, arterioles, venules, and shunts).	Microvascular damage in SSc, PAH (assessment of pulmonary damage)
Laser Doppler Flowmetry (LDF)	Assesses skin perfusion by measuring the Doppler effect induced by coherent light scattering related to red blood cell movement.	-Heatable fiber optic probe -Can detect both tissue perfusion and skin temperature -Optimal time resolution	-Measurement of blood flow at one point -Lack of reproducibility -Contact technique, limited to probe site -Measurement of local tissue perfusion (capillaries, arterioles, venules, shunts)	Microvascular damage in SSc
Laser Doppler Perfusion Imaging (LDPI)	-A laser with a standard output wavelength (color) directed against a diffusion medium such as skin or blood -A Doppler shift (color change) is induced by moving objects, such as blood cells, in scattered light	-Measurement of blood flow of an entire area -Non-contact technique -Good reproducibility	-Slow data acquisition -Measurement of skin perfusion (capillaries, arterioles, venules, and shunts) -Poor temporal resolution	PRP and vascular involvement in SSc
Thermography	Indirect measurement of blood flow	Non-contact technique	Indirect measurement of blood flow	Microvascular damage in SSc
Near infrared spectroscopy 2D imaging (NIRS-2D)	-Assess regional tissue oxygenation and microvascular function, in conjunction with vascular occlusion testing	-Non-invasive technique -Evaluation of vascular function by measuring blood flow	-Indirect measurement of blood flow -Low spatial resolution and poor sensitivity	Microvascular damage in SSc
Photoplethysmography (PPG)	It uses infrared light to measure changes in blood volume	Non-invasive technique	Its application in Raynaud’s phenomenon to evaluate digital artery response to cold test and medications has so far been limited	Microvascular damage in SSc
Infrared thermography (IRT)	Through digital thermal cameras, it records and quantifies the skin thermoregulation process, evaluating digital perfusion.	Predictor of higher probability of developing DU and need of surgical debridement	It requires careful monitoring of acclimatization time, camera-to-individual distance, ambient temperature, and humidity, as well as proper subject characterization.	Evaluation of PRP in patients with SSc
Nailfold videocapillaroscopy (NVC)	Method for an early diagnosis and follow up of nailfold microangiopathy combining a microscope (with a 5-million-pixels system) and a digital video camera.	Noninvasive, safe, inexpensive, reproducible, and validated method to assess morphological impairment in SSc	Need for further investigation	Microvascular damage in SSc and efficacy of treatment, PAH, ILD (assessment of pulmonary damage and heart involvement)

HS, healthy subjects; PBP, peripheral blood perfusion; SSc, systemic sclerosis; PRP, primary Raynaud’s phenomenon; IRT, infrared thermography; SLE, systemic lupus erythematosus; and DU, digital ulcers.