Multispectral image analysis for patient tissue tracking during complex interventions

During complex interventions, patient tracking is needed for optimal motion compensation, in order to guide the physician in a minimally invasive way. Nowadays, optical tracking systems are used for tracking of markers. Despite the unobtrusiveness of this technology, the approach is cumbersome because it requires manual placement of markers, which can alter during the operations due to the presence of liquids. To improve the clinical workflow, a new feature tracking algorithm is designed, involving feature detection and tracking without optical markers. The new markers are created with the multispectral imaging. Maximally stable extremal regions (MSER) and Speeded Up Robust Feature (SURF) methods are applied to design features and track natural landmarks, e.g. moles and veins. Both methods are tested and compared in accuracy with the mean shift tracking method. SURF reaches the highest accuracy of 0.257 pixels for images at 430 nm and 0.562 pixels for images at 970 nm. This study shows that incorporating multispectral imaging in the surgical scenario leads to an attractive benefit minimizing the risk of marker obstruction and displacement

Age-related heart rate response to exercise in heart transplant recipients. Functional significance

The heart rate (HR) and O2 uptake (V̇O2) responses to cycle ergometer exercise and the role of O2 transport in limiting submaximal and maximal aerobic performance were assessed in 33 heart transplant recipients (HTR) [14 children (P-HTR), 11 young adults (YA-HTR) and 8 middle-age adults (A-HTR)] and in 28 age-matched control subjects (CTL). In 7 P-HTR ("responders") the HR response to the onset of exercise (on-response) was as fast as that of CTL, whereas in all other patients ("non-responders") the HR on-response was typical of the denervated heart. Compared with non-responder P-HTR, responder P-HTR were also characterized by a normal peak HR (177±16 vs. 151±25 beats/min), an equally slow time constant for the V̇O2 on-response (τ: 54±11 vs. 62±13 s) and a similar low (∼60% of that of CTL) peak V̇O2 (28±7 vs. 26±10 ml/kg per min). On the other hand non-responder YA-HTR and A-HTR were characterized by a relatively low peak HR (151±21 and 144±29 beats/min, respectively), a slow τ for the V̇O2 on-response (63±12 and 70±11 s) and a low peak V̇O2 (28±7 and 19±6 ml/kg per min). In conclusion, a sizeable number of paediatric patients (responder P-HTR) may reacquire the normal HR response to exercise, both in terms of kinetics and maximal level. Despite the almost complete recovery of cardiovascular function, and, probably, oxygen delivery, both the kinetics of the V̇O2 on-response and the maximal aerobic power of the responder P-HTR were similar to those of non-responder P-HTR. The latter finding is probably attributable to peripheral limitations, due to inborn and/or pharmacological muscle deterioration

Multispectral image analysis for patient tissue tracking during complex interventions

During complex interventions, patient tracking is needed for optimal motion compensation, in order to guide the physician in a minimally invasive way. Nowadays, optical tracking systems are used for tracking of markers. Despite the unobtrusiveness of this technology, the approach is cumbersome because it requires manual placement of markers, which can alter during the operations due to the presence of liquids. To improve the clinical workflow, a new feature tracking algorithm is designed, involving feature detection and tracking without optical markers. The new markers are created with the multispectral imaging. Maximally stable extremal regions (MSER) and Speeded Up Robust Feature (SURF) methods are applied to design features and track natural landmarks, e.g. moles and veins. Both methods are tested and compared in accuracy with the mean shift tracking method. SURF reaches the highest accuracy of 0.257 pixels for images at 430 nm and 0.562 pixels for images at 970 nm. This study shows that incorporating multispectral imaging in the surgical scenario leads to an attractive benefit minimizing the risk of marker obstruction and displacement

The heart rate response to exercise and circulating catecholamines in heart transplant recipients

The plasma concentration of noradrenaline ([NA]) is higher than that of adrenaline ([A]) both in normal subjects and in heart transplant recipients (HTR). Since in both groups the myocardial density of β1-adrenergenic receptors is much greater than that of β2-adrenergenic receptors, the chronotropic response of a denervated heart to changes in plasma [NA] and [A] in the absence of reinnervation should be similar to that of agonist stimulation of β1-receptors. To test this hypothesis, 17 HTR and 9 healthy subjects (CTL) performed incremental exercise on a cycle ergometer to voluntary exhaustion. Heart rate (HR) was recorded by electrocardiography. [NA] and [A] were measured by high-pressure liquid chromatography at rest and at increasing workloads (ẇ). In both groups, HR and [NA+A] increased with ẇ, and HR with [NA+A]. Normalized HR values, plotted against the logarithm of [NA+A], fitted significantly logistic curves. The affinity constants were different, i.e. 2599±350 and 487±37 ng·1-1, for HTR and CTL, respectively. The chronotropic effect of changes in [NA+A] in HTR was similar to that of combined β1- and β2-adrenergic activation evoked by applying isoprenaline to isolated heart myocytes (Brodde OE, Pharmacol Ther 60:405-430, 1993). These findings suggest that over time sympathetic reinnervation and the modulation of β-receptors may take place in HTR, ruling out the hypothesis of persistent heart denervation