Compact electron spin resonance skin oximeter: Properties and initial clinical results.

PURPOSE: Skin oxygen level is of significance for the diagnosis and treatment of many clinical problems, such as chronic wounds and diabetic foot ulcers. Furthermore, skin oxygen levels can be correlated to arterial oxygen partial pressure, thereby revealing potentially dangerous conditions such as hyperoxia (too much oxygen), which may occur in ventilated neonates. Traditionally, skin oxygen levels are measured using electrochemical methods and, more recently, also by fluorescence lifetime techniques. These approaches suffer from several drawbacks, rendering them suboptimal. The purpose of this work is to develop an electron spin resonance (ESR) -based method for monitoring oxygen partial pressure (pO2 ) in skin tissue. METHODS: A compact sensor for pulsed ESR is designed and constructed. Our ESR-based method makes use of a unique exogenous paramagnetic spin probe that is placed on the skin in a special partially sealed sticker, and subsequently measuring its signal with the compact pulsed ESR sensor that includes a miniature magnet and a small S-band (~2.3 GHz) microwave resonator. The inverse of the spin-spin relaxation time (1/T2 ) measured by ESR is shown to be linearly correlated with pO2 levels. RESULTS: The sensor and its matching sticker were tested both in vitro and in vivo (with human subjects). Measured skin pO2 levels reached equilibrium after ~2-3 h and were found to be comparable to those measured by continuous-wave (CW) ESR using a large electromagnet. CONCLUSIONS: A compact pulsed ESR sensor with a matching paramagnetic sticker can be used for pO2 monitoring of the skin tissue, similar to large bulky CW ESR systems.

Electron-Spin-Resonance Dipstick.

Electron spin resonance (ESR) is a powerful analytical technique used for the detection, quantification, and characterization of paramagnetic species ranging from stable organic free radicals and defects in crystals to gaseous oxygen. Traditionally, ESR requires the use of complex instrumentation, including a large magnet and a microwave resonator in which the sample is placed. Here, we present an alternative to the existing approach by inverting the typical measurement topology, namely placing the ESR magnet and resonator inside the sample rather than the other way around. This new development relies on a novel self-contained ESR sensor with a diameter of just 2 mm and length of 3.6 mm, which includes both a small permanent magnet assembly and a tiny (∼1 mm in size) resonator for spin excitation and detection at a frequency of ∼2.6 GHz. The spin sensitivity of the sensor has been measured to be ∼1011 spins/√Hz, and its concentration sensitivity is ∼0.1 mM, using reference samples with a measured volume of just ∼10 nL. Our new approach can be applied for monitoring the partial pressure of oxygen in vitro and in vivo through its paramagnetic interaction with another stable radical, as well as for simple online quantitative inspection of free radicals generated in reaction vessels and electrochemical cells via chemical processes.

The three-dimensional geometric relationship between the mitral valvar annulus and the coronary arteries as seen from the perspective of the cardiac surgeon using cardiac computed tomography.

OBJECTIVES: Mitral annuloplasty involves sewing a prosthetic ring to the mitral annulus. This involves a risk of damaging the surrounding structures in the left atrioventricular (AV) groove, particularly the left circumflex artery, which may be inadvertently sutured, causing an arterial occlusion. We have used cardiac computed tomography (CT) scans to study the three-dimensional relationship between the mitral valvar annulus and the neighbouring coronary arteries in the AV groove, and to map the distance between the arteries and the annulus. METHODS: We examined cardiac CT scans of two groups of patient: 40 normal subjects, and 30 patients with left ventricular dysfunction and/or mitral regurgitation. The hinge line of the mitral valve, as well as the location of the coronary arteries within the left AV groove, was manually marked on a workstation and three-dimensional coordinates saved in digital format. Dedicated software was developed to calculate the plane of the mitral annulus, and the smallest distance between each point on the annulus and each of the left circumflex and right coronary arteries, called local minima. The global minimum for each heart is defined as the minimum of all local minima. RESULTS: The global minimum for the left circumflex averaged 6.4 ± 2.1 mm, usually involving the proximal portion, just laterally to the left trigone. In three-tenths of patients, the global minimum was <5 mm. This was more common in patients with left dominance, and in the normal subjects. The major component of the line vector between the annulus and circumflex is parallel to the plane of the mitral annulus, while the perpendicular component is usually in an atrial direction. For the dominant right coronary artery (RCA), the global minimum distance to the annulus is 14.7 ± 5.7 mm. In no patient did the RCA approach to within 5 mm with respect to the mitral annulus, albeit that 13% were <10 mm. CONCLUSIONS: In a significant proportion of patients, the left circumflex is in very close proximity to the annulus of the mitral valve. Knowledge of the precise three-dimensional relationships between the structures can be expected to minimize iatrogenic complications.