Cath Lab Digest

From *Georgetown University Hospital, Washington, D.C. and §State University of New York, Syracuse, New York.

Manuscript submitted June 24, 2009 and accepted September 8, 2009.

Correspondence: Richard Neville, MD, Georgetown University Hospital, Division of Vascular Surgery, 3800 Reservoir Rd, 4PHC, Washington, DC 20007. E-mail: neviller@gunet.georgetown.edu

Disclosure: The authors report no conflicts of interest regarding the content herein.

ABSTRACT
Hyperspectral tissue oxygenation mapping (HTOM) is a new imaging modality that is able to evaluate tissue perfusion at the microcirculatory level by measuring oxyhemoglobin, deoxyhemoglobin, and oxygen saturation levels. This study establishes a database of normative values for HTOM to guide further utilization of this diagnostic modality. Methods. HTOM technology quantifies tissue oxygenation with quantitative and spatial analysis. To establish normative values, HTOM was used to scan 11 anatomical regions on 194 subjects without symptomatic vascular disease. Oxyhemoglobin, deoxyhemoglobin, and oxygen saturation values were obtained in all regions for all subjects. To evaluate reproducibility, a subgroup (n=74) returned 8 hours later for scans of the same anatomic sites. Another subgroup (n=19) underwent cuff ischemia testing to assess the performance of HTOM in a simulation of microvasculature ischemia. Results. One hundred and ninety-four subjects (93 male, 101 female, age range 18–80) completed anatomic site assessments. Normative values were obtained for anatomic regions on the lower and upper extremity. The values for oxyhemoglobin, deoxyhemoglobin, and oxygen saturation varied with anatomic location with plantar and palmar surfaces demonstrating highest baseline perfusion. No significant differences in HTOM values were noted at the 8-hour repeat evaluation. A decrease in perfusion occurred during cuff induced ischemia followed by reperfusion and a return to baseline. Conclusion. A database of normative ranges for oxyhemoglobin, deoxyhemoglobin, and oxygen saturation has been obtained to serve as reference values for future HTOM analysis. These data will provide a comparative construct to study hyperspectral imaging and its role in the diagnosis and treatment of vascular disease.

Introduction

Non-invasive vascular laboratory testing is important in detecting the severity of chronic limb ischemia (CLI). However, definitive methods are lacking to discern the functional state of perfusion at the microcirculatory level. Oxygen delivery, extraction, and saturation are key parameters to be considered when evaluating the state of the microvasculature in CLI, especially in regard to diabetes mellitus and wound healing. Hyperspectral imaging (HTOM) has already been used in several clinical scenarios, including discovering early changes in the microcirculation of the diabetic foot,¹ predicting clinical outcomes in diabetic foot ulcers,² maximizing limb preservation in amputation planning,³ assessing of shock,^4,5 and identifying residual tumor tissue during breast cancer surgery.^6,7

However, in order to take full clinical advantage of possible CLI applications, a normative database of values is needed to establish reference values of tissue perfusion, providing a comparative analysis for diseased states, thereby improving the technology’s clinical applicability. This study addresses the need to provide clinicians with a profile of normative value ranges for oxyhemoglobin and deoxyhemoglobin as measured by hyperspectral imaging. The study also examines anatomic variations and reproducibility in these normative values for oxyhemoglobin, deoxyhemoglobin, and oxygen saturation.

Methods

The study enrolled 194 subjects with no symptoms of peripheral arterial or venous disease. Patients having diabetes mellitus, hypertension, or any known peripheral vascular disease were excluded from participation. The study was conducted at a single center with institutional IRB approval and written informed consent. Adverse events were monitored and reported. There were 93 males and 101 females studied. Subjects ranged in age from 18 to 80 years of age, with a mean of 42 ± 14. Racial distribution included 64 Caucasians (33.2%), 51 African Americans (26.4%), 43 Asians (22.3%), and 35 Hispanics (18.1%). Subjects included 125 non-smokers, 42 current smokers (21.8%), and 27 with a past history of smoking.

Tissue oxygenation images were collected with a commercial hyperspectral imaging system (OxyVu, HyperMed, Inc., Burlington, Massachusetts). This hyperspectral imaging system obtains multiple images at discrete wavelengths, providing a diffuse reflectance spectrum for each pixel in the hyperspectral image. The system uses wavelengths between 500 and 660 nm to correspond to a region that includes two absorption peaks from oxyhemoglobin and one absorption peak from deoxyhemoglobin. Tissue oxygenation images or maps were constructed from oxyhemoglobin, and deoxyhemoglobin values determined from each pixel in the image. Prior to imaging each patient, the system was calibrated to a reflectance card (OxyVu CheckPad, HyperMed). Patients were imaged on a standard examination table or reclining chair. A fiducial target (OxyVu Target, HyperMed) was placed near the center on the image field of view to facilitate image realignment (image registration) and to correct for patient movement when collecting multiple images.