Written by: Dr. Robert L. Bard | Lennard M. Gettz, Ed.D | Noelle Cutter, PhD
PART 2: VERIFYING SIGNS OF COVID-19 STROKE THROUGH IMAGING
By: Robert L. Bard, MD and Dr. Pierre Kory, MD
We have learned over the last century that blockages of coronary arteries to the heart and carotid arteries to the brain are precipitated by inflammation of the inner walls of the vessel, called the “intima”
However, the chronic and diffuse nature of arteritis often weakened the vessel wall producing aneurysmal dilation and rupture. Today we find sophisticated non-invasive or minimally invasive modalities to be the first line of interrogation of vasculitis. 
|- Carotid Sonogram
- Carotid Doppler
- Eye Sonography
- Transorbital Doppler
- Contrast Enhanced Ultrasound
- Transcranial Doppler
- Hybrid Imaging
|- 3D/4D Vessel Density Histogram
- Endoarterial 3D Doppler
- Retinal OCT
- Soft Tissue OCT
- Reflectance Confocal Microscopy
- Small Coil MRI
- 7 Tesla MRI
DOPPLER IMAGING TECHNOLOGIES
- COLOR DOPPLER - most common application where red is flow towards the probe and blue is flow away from the probe
- POWER DOPPLER - higher spatial resolution without directional flow correlation
- 3D POWER DOPPLER - allows volumetric analysis of vessel density used in treatment correlation where more vessels means increased neovascularity and fewer vessels correlates with clinical improvement
- ANGIODOPPLER – similar to color Doppler with higher spatial resolution
- MICROVASCULAR DOPPLER-images capillary flow
- B-FLOW DOPPLER-not true flow technology but observes motion of red blood cells directly
CAROTID DOPPLER: Flow abnormalities of turbulence and absence are commonly evaluated with this modality. Plaque forms more readily in aberrant flow patterns and high velocity regions accompanying narrowing.
EYE SONOGRAPHY: Sonofluoroscopy of the orbital soft tissues and eyes is performed in multiple scan planes with varying transducer configurations and frequencies. Power and color Doppler use angle 0 and PRF at 0.9 at optic nerve head. 3D imaging of optic nerve and carotid, central retinal arteries and superficial posterior ciliary arteries performed in erect position before and after verbal communication. Retinal arterial flow is measured. Optic nerve head bulging is checked as increased intracranial pressure may be demonstrable.
TRANSORBITAL DOPPLER: R/L ciliary arteries have normal Doppler flows of 10cm/s which is symmetric.
CONTRAST ENHANCED ULTRASOUND: Widely used European nonionic contrast injection allows imaging capillary size vessels and perfusion characteristics
TRANSCRANIAL DOPPLER: This measures the flow in the anterior, middle and posterior cerebral arteries as well as Circle of Willis.
3D/4D VESSEL DENSITY HISTOGRAM: Multiple image restoration and reconstruction shows retinal vessel density of 25% at the optic nerve head and adjacent region with quantitative accuracy.
ENDOARTERIAL 3D DOPPLER: Microcatheters inserted into the arterial or venous system provide measurement of wall thickness and presence of inflammatory vessels inside the intima.
RETINAL OCT: Subtraction techniques done with OCT optical coherence tomography may show changes in the caliber of the retinal vessels with verbal ideation.
SOFT TISSUE OCT: The depth of penetration may be extended to 2-3mm allowing for analysis of vascular changes in erythematous or erythropoor dermal areas. Thrombosis may be observed.
REFLECTANCE CONFOCAL MICROSCOPY: This microscopic analysis of the cells also quantifies microvascular pathology and is a potential modality for studying vasculitis.
SMALL COIL MRI: High resolution systems used for animal study and superficial organs can image the intra-arterial anatomy including dynamic contrast imaging on standard 1.5T and 3T units.
7 TESLA MRI: High field systems analyze signal abnormalites rapidly with high resolution.
HYBRID IMAGING: Hybrid imaging refers to combining diagnostic modalities to assess disease and monitor therapy.
1) Hemodynamics: https://en.wikipedia.org/wiki/Hemodynamics
3). Hassani SN, Bard RL: Ultrasonic Diagnosis of Aortic Aneurysms. J. Natl. Med. Assoc. 66:298-299, July 1974
4). Lande A, Bard RL: Arteriography of Pedunculated Splenic Cysts. Angiology 25:617-621, October 1974
5). Lande A, Bard RL, Rossi P: Takayasu's Arteritis: A World Entity. N.Y. State J. Med. 76:1477-1482, Sep 1976
6). Helbick Eur Radiol 30:5536-5538, 2020
7). Mao l JAMA Neurol 2020 77:683-690
8). Bard RL , Gettz L, van der Bent S etal: Proceedings of the 4th Inflammatory Disease Summit at NY Academy of Medicine Nov 2021