Milica M. Jankovic

Recovery of motor function after stroke: a polymyography-based analysis

We present a method for assessing muscle activation patterns during goal-directed movement. We present a cohort study from a randomized clinical trial that followed the recovery of motor function during and after intensive gait training, assisted by sensor-driven, four-channel electrical stimulation. The instrument that we developed allows for the simultaneous recordings of up to 16 channels that are wirelessly sent to a host computer, which then provides feedback to the subject. The inputs to the portable instrument support electromyography (EMG) amplifiers, inertial sensors and goniometers. We show that this method is sensitive enough to show changes in muscle activation patterns in stroke patients before and after gait training (four weeks, five days a week, 30 min daily). We also show that the recovery decreases the differences between patterns of muscle activities (e.g., levels of muscle activations and median frequencies) assessed in hemiplegic and healthy subjects. This method allows for the analysis of muscle contributions and activation patterns; therefore, it might be possible to better understand the physiology behind the recovery of function. This EMG analysis provides a quantification of recovery that is a valuable addition to other measures, such as the Fugl-Meyer score, the Berg-Balance score, gait speed, and the symmetry index.

Myocardial mechanical and QTc dispersion for the detection of significant coronary artery disease

AIMS Ischaemic but viable myocardium may exhibit prolongation of contraction and QT interval duration, but it is largely unknown whether non-invasive assessment of regional heterogeneities of myocardial deformation and QT interval duration could identify patients with significant coronary artery disease (CAD). METHODS AND RESULTS We retrospectively studied 205 patients with suspected CAD who underwent coronary angiography. QTc dispersion was assessed from a 12-lead electrocardiogram (ECG) as the difference between the longest and shortest QTc intervals. Contraction duration was assessed as time from the ECG R-(Q-)wave to peak longitudinal strain in each of 18 left ventricular segments. Mechanical dispersion was defined as either the standard deviation of 18 time intervals (dispersionSD18) or as the difference between the longest and shortest time intervals (dispersiondelta). Longitudinal strain was measured by speckle tracking echocardiography. Mean contraction duration was longer in patients with significant CAD compared with control subjects (428 ± 51 vs. 410 ± 40 ms; P = 0.032), and it was correlated to QTc interval duration (r = 0.47; P < 0.001). In contrast to QTc interval duration and dispersion, both parameters of mechanical dispersion were independently associated with CAD (P < 0.001) and had incremental value over traditional risk factors, wall motion abnormalities, and global longitudinal strain (GLS) for the detection of significant CAD. CONCLUSION The QTc interval and myocardial contraction duration are related to the presence of significant CAD in patients without a history of previous myocardial infarction. Myocardial mechanical dispersion has an incremental value to GLS for identifying patients with significant CAD.

An EMG system for studying motor control strategies and fatigue

We present a system for polymyographic analysis which addresses detection of muscle fatigue and strategies assumed by the central nervous system to deal with it. The system consists of EMG amplifiers, force transducers, A/D converter, portable computer and software running in the LabView environment that allows real-time and detailed offline processing of EMG signals in time and frequency domains. We demonstrate the features of the system by using the example of analyzing the strategy to generate 80% percent of the maximum force for prolonged period of time. Force sensor was used to detect muscle fatigue (fall of the force bellow the selected threshold), and EMG recordings were used for the analysis which of the quantitative measures of EMG is correlated with this. We tested the following four methods of EMG measures: 1) median frequency, 2) short-time mean frequency, 3) mean frequency of scalogram and 4) fractal dimension. We show that the system is capable of providing reproducible results and could be used for diagnostics and basic research in motor control. The analysis shows that the median frequency used often is not the best predictor of fatigues, and the measure needs to be selected based on the relative activity of the muscle compared to its maximal activity.

First steps in new affordable PIV measurements

Particle image velocimetry (PIV) is an optical, laser based, measurement of fluid velocity and its 2D/3D visualisation. We have presented a new approach in low-cost PIV design using: 1) fast industrial camera, 2) laser pointer, with cylindrical lens for continual fluid flow illumination, 3) acquisition software developed in house, 4) OpenPIV analysis software. Velocity was measured in the glass jar where swirl flow was generated by magnetic stirrer. In this pilot study, results obtained by calibration device based on Laser Doppler anemometry and our PIV results are in good agreement.

GammaKey system for improved diagnostics with gamma cameras.

We designed the GammaKey system for the acquisition, storage and analysis of images from semi-analogue gamma scintillation cameras (GSCs). The GammaKey system, operating on a standard PC, replicates the functionality of earlier dedicated computer systems, allows the exchange of data in the DICOM format and has an open architecture enabling the development of new diagnostic techniques. The main purpose of the GammaKey is to enable the continued use of old GSCs which have functional scintillation crystals, but also to permit data exchange with new digital GSCs. The GammaKey has been technically validated by standards established by the National Electrical Manufacturers Association. The GammaKey has been used for seven years in two leading centres for nuclear medicine in Serbia (the Clinical Center of Serbia, Belgrade, and the Clinical Center of Vojvodina, Novi Sad) in approximately 30,000 patients. Clinical application proves that the GammaKey is a robust and reliable system with high-quality image output. Data processing can be upgraded with non-standard features added on request as shown in two examples: (1) the testing of splenectomy efficacy in the case of thrombocytopenia with normal production; and (2) the detection and localisation of parathyroid adenomas.

Clustering Technique for Quantitative Assessment of Motor Function in Stroke Patients

We designed a quantification method for assessment of motor function in stroke patients. The method is based on clustering of data from polymyography (pEMG) recordings of the lower leg. We recorded pEMG in healthy subjects and hemiplegic patients during well-controlled single joint voluntary movement – ankle dorsiflexion. Agglomerative Hierarchical Clustering (AHC) method is applied on relative contribution parameters of muscles during dorsiflexion. AHC method differentiated three clusters: cluster of stroke patients at the therapy onset, cluster of stroke patients after Functional Electrical Therapy (FET) therapy, and cluster of healthy subjects, when applied on the parameters obtained from tibialis anterior muscle and rectus femoris muscle. The presented results indicate that the applied clustering technique might be used as a means for studying muscle activation patterns.

T-wave changes in patients with Wellens syndrome are associated with increased myocardial mechanical and electrical dispersion

Some patients with unstable angina and critical stenosis of the left anterior descending coronary artery (LAD) present with Wellens syndrome (WS), i.e., inverted or biphasic T-waves in the anterior precordial leads. We assessed clinical, angiographic, electro- and echocardiographic characteristic of patients with WS. In this retrospective study, clinical, angiographic, electro- and echocardiographic characteristic of 35 patients with WS were compared to 57 patients with critical LAD stenosis and normal resting electrocardiogram (ECG), and 45 subjects with normal coronary angiogram. QTc dispersion was measured from the 12-lead ECG as the difference between longest and shortest QTc intervals. Mechanical dispersion was defined as the time difference between the longest and shortest contraction durations which were measured as the time from the first deflection of the QRS complex to maximum myocardial shortening of each 18 segmental longitudinal strain curves derived by speckle tracking echocardiography. There were no significant differences in the complexity and location of the LAD lesion, anterograde and collateral flow in LAD and coronary artery dominance between patients with WS and normal ECG (P > 0.05, for all). Patients with WS had lower global longitudinal strain (GLS) and more pronounced both QTc and myocardial mechanical dispersion than patients with critical LAD stenosis and normal ECG, and control subjects (P < 0.05). T-wave changes in patients with WS are associated with more profound regional myocardial dysfunction and increased QTc and myocardial mechanical dispersion. Similar angiographic characteristics of the LAD lesion were seen in patients with WS and normal ECG.

Microfluidic Chip Fabrication for Application in Low-Cost DIY MicroPIV

The article presents the process of fabrication of the microfluidic chip to be used with the do-it-yourself (DIY) micro-PIV system previously made and compared to the classic PIV setup. This pilot study is an example of research being conducted in the Scientific fab lab (fabrication laboratory), founded at the Faculty of Mechanical Engineering, University of Belgrade. Fab labs and DIY principle are becoming more and more accepted by the scientific community and this article aims to contribute to such trend.

Clustering of time activity curves for uptake pattern assessment in dynamic nuclear medicine imaging

Nuclear medicine instrumentation visualize the radiopharmaceutical uptake inside the body allowing the interpretation of physiological processes. In dynamic nuclear medicine imaging, time-dependent image sequences are recorded. The changes of radiopharmaceutical uptake over time (so calles time activity curves, TACs) can be analyzed in order to find abnormal patterns corresponding to either structural or functional disorders. Hierarchical Cluster Analysis (HCA) is a powerful statistical tool for classification. We applied HCA on TACs to find clusters of similar TAC patterns. Optimal number of clusters is determined by Huberts rule. We used Principal Component Analysis (PCA) on TAC clusters to find a representative TAC that presents the uptake pattern in the region of each cluster. The application of algorithm is illustrated in the patient with the histopatologically proven parathyroid hyperplasia, but the developed tool is useful for finding the appropriate classification method of TAC patterns in all types of dynamic nuclear medicine studies.

Third-party application for quantitative salivary gland scintigraphy

The classification criteria for Sjögrens syndrome includes the salivary gland scintigraphy (SGS) as one of objective tests for assessment of salivary gland function. We have developed the software for the automatic calculation of commonly investigated quantitative salivary and oral indices (maximum accumulation, maximum secretion, modified secretion velocity, uptake ratio, parotid : submandibular ratio, ejection fraction, pre-stimulatory and post-stimulatory oral activity) derived from dynamic SGS. Our software enables the standardization of processing protocols in multicenter studies.