Macromolecular degeneration and biochemical changes in tissue can be quantified using rotating fr... more Macromolecular degeneration and biochemical changes in tissue can be quantified using rotating frame relaxometry in MRI. It has been shown in several studies that the rotating frame longitudinal relaxation rate constant (R1ρ ) and the rotating frame transverse relaxation rate constant (R2ρ ) are sensitive biomarkers of phenomena at the cellular level. In this comprehensive review, existing MRI methods for probing the biophysical mechanisms that affect the rotating frame relaxation rates of the tissue (i.e. R1ρ and R2ρ ) are presented. Long acquisition times and high radiofrequency (RF) energy deposition into tissue during the process of spin-locking in rotating frame relaxometry are the major barriers to the establishment of these relaxation contrasts at high magnetic fields. Therefore, clinical applications of R1ρ and R2ρ MRI using on- or off-resonance RF excitation methods remain challenging. Accordingly, this review describes the theoretical and experimental approaches to the des...
We analyse biosignals recorded with a near field imaging floor sensor, using a test group of five... more We analyse biosignals recorded with a near field imaging floor sensor, using a test group of five people. This human tracking system is capable of non-contact biosignal recording. A time domain integration method is used to extract periodic cardiac waveforms from the raw signals, while an ECG signal is used as a trigger for windowing. The most favourable posture for cardiac monitoring is when the test subjects are lying prone on the sensor floor. A clear correlation between the test subjects can be found when waveforms in the lying prone or supine postures are compared. The respiration monitoring capability is also discussed.
IEEE journal of biomedical and health informatics, Jan 13, 2015
The vibrations produced by the cardiovascular system that are coupled to the precordium can be no... more The vibrations produced by the cardiovascular system that are coupled to the precordium can be noninvasively detected using accelerometers. This technique is called seismocardiography. Although clinical applications have been proposed for seismocardiography, the physiology underlying the signal is still not clear. The relationship of seismocardiograms of on the back-to-front axis and cardiac events is fairly well known. However, the three-dimensional6 vibrations detectable with modern accelerometers have not been quantified in terms of cardiac cycle events. A major reason for this might be the degree of inter-subject variability observed in three-dimensional seismocardiograms. We present a method to quantify threedimensional seismocardiography in terms of cardiac cycle events. First, cardiac cycle events are identified from the seismocardiograms and then assigned a number based on the location in which the corresponding event was found. 396 cardiac cycle events from 9 healthy subjec...
Background: Seismocardiography is the noninvasive measurement of cardiac vibrations transmitted t... more Background: Seismocardiography is the noninvasive measurement of cardiac vibrations transmitted to the chest wall by the heart during its movement. While most applications for seismocardiography are based on unidirectional acceleration measurement, several studies have highlighted the importance of three-dimensional measurements in cardiac vibration studies. One of the main challenges in using three-dimensional measurements in seismocardiography is the significant inter-subject variability of waveforms. This study investigates the feasibility of using a unified frame of reference to improve the inter-subject variability of seismocardiographic waveforms. Methods: Three-dimensional seismocardiography signals were acquired from ten healthy subjects to test the feasibility of the present method for improving inter-subject variability of three-dimensional seismocardiograms. The first frame of reference candidate was the orientation of the line connecting the points representing mitral valve closure and aortic valve opening in seismocardiograms. The second candidate was the orientation of the line connecting the two most distant points in the three dimensional seismocardiogram. The unification of the frame of reference was performed by rotating each subject's three-dimensional seismocardiograms so that the lines connecting the desired features were parallel between subjects. Results: The morphology of the three-dimensional seismocardiograms varied strongly from subject to subject. Fixing the frame of reference to the line connecting the MC and AO peaks enhanced the correlation between the subjects in the y axis from 0.42 ± 0.30 to 0.83 ± 0.14. The mean correlation calculated from all axes increased from 0.56 ± 0.26 to 0.71 ± 0.24 using the line connecting the mitral valve closure and aortic valve opening as the frame of reference. When the line connecting the two most distant points was used as a frame of reference, the correlation improved to 0.60 ± 0.22. Conclusions: The results indicate that using a unified frame of reference is a promising method for improving the inter-subject variability of three-dimensional seismocardiograms. Also, it is observed that three-dimensional seismocardiograms seem to have latent inter-subject similarities, which are feasible to be revealed. Because the projections of the cardiac vibrations on the measurement axes differ significantly, it seems obligatory to use three-dimensional measurements when seismocardiogram analysis is based on waveform morphology.
The sensor system presented in this paper utilizes near field imaging for wide area human locatio... more The sensor system presented in this paper utilizes near field imaging for wide area human location and tracking. The sensor system provides reliable location data of humans by measuring slight impedance changes between elements of a thick film sensor matrix under the floor covering. The sensor is completely rigid and undetectable. The low cost and scalable design allows the system to be spread across the whole indoor surface area. The system aims to ensure the efficiency of the elderly care system. Ageing of the population structure in Finland generates an eminent need for more resources in this field. The main pilot sites of the described system are in the senior homes, where the personnel will be most stressed in the near future. The location data can be used for various purposes such as making alarms of senior persons getting up from bed during the night risking them selves of losing balance. Making an alarm during falling down on the floor has an obvious benefit for the habitants of old age homes.
This report illustrates the technical design for the monitoring system of well- being and demonst... more This report illustrates the technical design for the monitoring system of well- being and demonstrates its feasibility in elderly people. The Con-Dis device consists of three buttons with a happy, neutral or unhappy face, each describing the mood of the patient. The functionality of the device was tested on 5 test persons who were asked to demonstrate their state of
In this study, an improved version of the low-frequency indoor location system, with a larger det... more In this study, an improved version of the low-frequency indoor location system, with a larger detection range and more durable antenna laminate, is presented. The basic system uses quad antennas, placed under the floor surface, to locate tags with 125-kHz radio signals. The improvements were achieved with a one-layer laminate construction and transmitter electronics that can feed larger currents to the antennas. The measured tag detection height was 2 m, which is adequate for location applications. The low-frequency signal was not affected by normal objects. The tag location reliability of 96.3% was verified with a practical test. Keywords Indoor location • Low frequency • Near field imaging • Signal penetration 1 Introduction Pervasive and context-aware computing often requires information about the locations and trajectories of people in an indoor environment where GPS, or related positioning, is not available [1]. Applications vary from interactive environments to health care informatics. To satisfy this need, different types of indoor location systems have been created in recent years. The location methods can be roughly divided into active and passive ones. Passive methods observe the person's body itself. This can be done using cameras [2,3], measuring the static [4,5] or dynamic [6] weight distribution, or measuring the body capacitance [7-10]. These methods produce very high tracking accuracies (18-41 cm [3,10,13]); however, no identification takes place. Remote biometric identification with passive methods
In healthcare environment, different kinds of automatic solutions have been created to monitor an... more In healthcare environment, different kinds of automatic solutions have been created to monitor and track patients, for example near-field imaging and low-frequency RFID. The problem has been how to use the context-based data these systems produce and how to show the related information to the nursing staff. This paper shows how hospital data can be automatically transmitted to people using location information. The information is transmitted to a name tag that has wireless connectivity and touch screen with electric paper. This concept is piloted with a test application.
Background: Tomographic imaging has revealed that the body mass index does not give a reliable st... more Background: Tomographic imaging has revealed that the body mass index does not give a reliable state of overall fitness. However, high measurement costs make the tomographic imaging unsuitable for large scale studies or repeated individual use. This paper reports an experimental investigation of a new electromagnetic method and its feasibility for assessing body composition. The method is called body electrical loss analysis (BELA). Methods: The BELA method uses a high-Q parallel resonant circuit to produce a time-varying magnetic field. The Q of the resonator changes when the sample is placed in its coil. This is caused by induced eddy currents in the sample. The new idea in the BELA method is the alter.ed spatial distribution of the electrical losses generated by these currents. The distribution of losses is varied using different excitation frequencies. The feasibility of the method was tested using simplified phantoms. Two of these phantoms were rough estimations of human torso. One had fat in the middle of its volume and saline solution in the outer shell volume. The other had reversed conductivity distributions. The phantoms were placed in the resonator and the change in the losses was measured. Five different excitation frequencies from 100 kHz to 200 kHz were used. Results: The rate of loss as a function of frequency was observed to be approximately three times larger for a phantom with fat in the middle of its volume than for one with fat in its outer shell volume. Conclusions: At higher frequencies the major signal contribution can be shifted toward outer shell volume. This enables probing the conductivity distribution of the subject by weighting outer structural components. The authors expect that the loss changing rate over frequency can be a potential index for body composition analysis.
Medical & Biological Engineering & Computing, 2006
A simple objective screening method for diagnosis of the atrial septal defect (ASD) is needed. Ac... more A simple objective screening method for diagnosis of the atrial septal defect (ASD) is needed. Acoustic signals were collected from 61 children with ASD and 60 with a physiological murmur. The second heart sound (S 2) and the spectrum of systolic murmur were analysed. A statistical model was designed using stepwise logistic regression analysis. Significant variables distinguishing pathological form normal findings were the interval between the first heart sound and the beginning of systolic murmur or the respiratory variation of S 2 , and the frequency of the murmur at its maximum intensity. The area under the ROC curve was 0.922; indicating very good fit of the model and the confidence interval was 0.872-0.971. The sensitivity of the model was 91% and the specificity 73%. The analysis of acoustic findings from the heart is a valuable tool in diagnosing ASD. The next step will be automating this process.
In order to optimize head and neck magnetic resonance (MR) imaging with the spin-lock (SL) techni... more In order to optimize head and neck magnetic resonance (MR) imaging with the spin-lock (SL) technique, the T1ρ relaxation times for normal tissues were determined. Furthermore, T1ρ was compared to T1 and T2 relaxation times. Ten healthy volunteers were studied with a 0.1 T clinical MR imager. T1ρ values were determined by first measuring the tissue signal intensities with different
Aim: To develop an objective diagnostic method that facilitates detection of noncyanotic congenit... more Aim: To develop an objective diagnostic method that facilitates detection of noncyanotic congenital heart diseases.
This paper describes open-source hardware to measure both the magnitude and phase of the electric... more This paper describes open-source hardware to measure both the magnitude and phase of the electrical bioimpedance in a frequency range from few kilohertz up to 100 kHz by using a four-electrode technique. The amount of current injected and the sensitivity of the system can be set to the desired range by changing the front-end resistor values. The system can be easily built and adapted with the help of the design details made available at GitHub. The practical performance was evaluated in abdominal impedance measurement, which was the primary motivation to build the system. Other experiments were performed with a 2R-1C circuit, a 10-Ω resistor, and a 100-nF capacitor, with observed relative errors in the impedances of -0.73 ± 0.34 %, -2.47 ± 1.43 % and -8.81 ± 0.64 % (mean ± SD), respectively, from 10 kHz to 100 kHz.
Ultra-low-field magnetic resonance imaging (ULF MRI) in microtesla fields is a new technology wit... more Ultra-low-field magnetic resonance imaging (ULF MRI) in microtesla fields is a new technology with features unseen in tesla-range MRI. Instead of induction coils as sensors, superconducting quantum interference device (SQUID) sensors are used, providing a frequency-independent signal-to-noise ratio (SNR). Owing to its tolerance for large relative imaging-field inhomogeneities, electromagnet shimming is not necessary. ULF MRI can also be combined with magnetoencephalography (MEG) to image the brain with close to millimetre-millisecond resolution. In this paper, the hybrid MEG-MRI device developed at Aalto University will be presented, as well as a 3D imaging scheme combining gradient-excitation encoding with frequency and phase and encodings. It is noteworthy that, regarding the presented gradient-excitation encoding in ULF MRI, the kilohertz-range Larmor frequencies allow MR signals to propagate unattenuated through tissue, which is not the case in tesla-range MRI with Larmor frequencies even above 100 MHz. Thus, the presented encoding method is especially compatible with ULF MRI, where the use of three different encoding mechanisms for three-dimensional imaging is possible. The feasibility of image reconstruction with the gradient-excitation-encoding method is demonstrated by simulations.
-based evaluation of geometric distortions in functional MRI and diffusion tensor imaging (DTI) w... more -based evaluation of geometric distortions in functional MRI and diffusion tensor imaging (DTI) was investigated. An acrylic water-filled phantom with a grid structure was designed and manufactured to provide accurate geometric information over the volume measured in human brain imaging. The grid structures were well detected in data acquired using a 3-T MRI scanner with echo-planar imaging (EPI) sequences commonly applied in functional MRI and DTI. A method for quantifying distortions in the phantom data was presented and applied for the images. The validity of the phantom for EPI was evaluated by quantitatively comparing the distortions present in and induced by the phantom and a human brain when imaged under identical conditions. The results suggest that the new phantom can reveal geometric distortions easily undermined by standard MRI phantoms. For example, prominent variability in the distortions was found as a function of the orientation of the diffusion-sensitizing gradient. Possible future applications for this type of phantom include quality assurance and calibration of the hardware and software used in EPI-based functional MRI and DTI. Magn Reson Med 57:754-763, 2007.
The present study was designed to evaluate tissue contrast characteristics obtained with the spin... more The present study was designed to evaluate tissue contrast characteristics obtained with the spin-lock (SL) technique by comparing the results with those generated with a magnetization transfer(MT)-weighted gradient echo [GRE, echo-time (TE) ؍ 40 ms] sequence. Twenty-eight patients with hepatic hemangiomas (n ؍ 14), or metastatic liver lesions (n ؍ 14) were imaged at 0.1 T by using identical imaging parameters. Gradient echo, single-slice off-resonance MT, and multiple-slice SL sequences were obtained. SL and MT-effects were measured from the focal liver lesions and from normal liver parenchyma. In addition, tissue contrast values for the liver lesions were determined. Statistically significant difference between the SL-effects of the hemangiomas and metastases, and also between the MT-effects of the lesions was observed (p < 0.02). Tissue contrast values for the lesions proved to be quite similar between the SL and MT techniques. Our results indicate that at 0.1 T multiple-slice SL imaging provides MT based tissue contrast characteristics in tissues rich in protein with good imaging efficiency and wide anatomical coverage, and with reduced motion and susceptibility artifacts.
In this work, novel methods are suggested for assessing signal parameters of the free induction d... more In this work, novel methods are suggested for assessing signal parameters of the free induction decay (FID) in nuclear magnetic resonance (NMR) experiments. The FID signal was recorded in a microtesla field and analysed to determine its relaxation time, amplitude, Larmor frequency and phase. The challenge was posed by the narrow line width, whose related effects were investigated through simulations, also. The developed methods give a new view on FID signal estimation in microtesla as well as lower and higher fields. It is shown that the transverse relaxation time of a sample can be accurately determined in the frequency domain by other means than the Lorentz peak half width. Also, with some realistic approximations, a simple functional form for the power spectrum Lorentz peak shape is proposed. As shown in this work, the inspection of the power spectrum instead of the absorption and dispersion Lorentzians is advantageous in the sense that the waveform is independent of the FID phase. The automatic and efficient methods presented in this work incorporate an integral exponential fit, the fit of the power spectrum Lorentz peak and two ways to determine the FID phase. When there are sufficiently many data points in the Lorentz peak, the power spectrum Lorentz peak shape fit provides a quick, simple and accurate way of determining the amplitude, relaxation time and Larmor frequency of the FID. In the measurements of this work, however, the narrow line width led to establishing a more applicable method which is based on the exponential decay of the Lorentz peak with a temporally moving power spectrum window.
Background: Body electrical loss analysis (BELA) is a new non-invasive way to assess visceral fat... more Background: Body electrical loss analysis (BELA) is a new non-invasive way to assess visceral fat depot size through the use of electromagnetism. BELA has worked well in phantom measurements, but the technology is not yet fully validated. Methods: Ten volunteers (5 men and 5 women, age: 22-60 y, BMI: 21-30 kg/m 2 , waist circumference: 73-108 cm) were measured with the BELA instrument and with cross-sectional magnetic resonance imaging (MRI) at the navel level, navel +5 cm and navel -5 cm. The BELA signal was compared with visceral and subcutaneous fat areas calculated from the MR images. Results: The BELA signal did not correlate with subcutaneous fat area at any level, but correlated significantly with visceral fat area at the navel level and navel +5 cm. The correlation was best at level of navel +5 cm (R 2 = 0.74, P < 0.005, SEE = 29.7 cm 2 , LOOCV = 40.1 cm 2 ), where SEE is the standard error of the estimate and LOOCV is the root mean squared error of leave-one-out style cross-validation. The average estimate of repeatability of the BELA signal observed through the study was ±9.6 %. One of the volunteers had an exceptionally large amount of visceral fat, which was underestimated by BELA. Conclusions: The correlation of the BELA signal with the visceral but not with the subcutaneous fat area as measured by MRI is promising. The lack of correlation with the subcutaneous fat suggests that subcutaneous fat has a minor influence to the BELA signal. Further research will show if it is possible to develop a reliable low-cost method for the assessment of visceral fat either using BELA only or combining it, for example, with bioelectrical impedance measurement. The combination of these measurements may help assessing visceral fat in a large scale of body composition. Before large-scale clinical testing and ROC analysis, the initial BELA instrumentation requires improvements. The accuracy of the present equipment is not sufficient for such new technology. Blomqvist et al. BioMedical Engineering OnLine 2011, 10:98
Background: A simple but countable electronic device has been developed to gain reliable informat... more Background: A simple but countable electronic device has been developed to gain reliable information on elderly patients' perceived well-being. The device has been tested and proven to be technically functional and countable. It was now tested in two care homes for the elderly and two private homes to evaluate if it provided solid information about the well-being of elderly persons. This report illustrates the practical usage of the device and shows its efficiency in gathering solid well-being information from the focus group.
Macromolecular degeneration and biochemical changes in tissue can be quantified using rotating fr... more Macromolecular degeneration and biochemical changes in tissue can be quantified using rotating frame relaxometry in MRI. It has been shown in several studies that the rotating frame longitudinal relaxation rate constant (R1ρ ) and the rotating frame transverse relaxation rate constant (R2ρ ) are sensitive biomarkers of phenomena at the cellular level. In this comprehensive review, existing MRI methods for probing the biophysical mechanisms that affect the rotating frame relaxation rates of the tissue (i.e. R1ρ and R2ρ ) are presented. Long acquisition times and high radiofrequency (RF) energy deposition into tissue during the process of spin-locking in rotating frame relaxometry are the major barriers to the establishment of these relaxation contrasts at high magnetic fields. Therefore, clinical applications of R1ρ and R2ρ MRI using on- or off-resonance RF excitation methods remain challenging. Accordingly, this review describes the theoretical and experimental approaches to the des...
We analyse biosignals recorded with a near field imaging floor sensor, using a test group of five... more We analyse biosignals recorded with a near field imaging floor sensor, using a test group of five people. This human tracking system is capable of non-contact biosignal recording. A time domain integration method is used to extract periodic cardiac waveforms from the raw signals, while an ECG signal is used as a trigger for windowing. The most favourable posture for cardiac monitoring is when the test subjects are lying prone on the sensor floor. A clear correlation between the test subjects can be found when waveforms in the lying prone or supine postures are compared. The respiration monitoring capability is also discussed.
IEEE journal of biomedical and health informatics, Jan 13, 2015
The vibrations produced by the cardiovascular system that are coupled to the precordium can be no... more The vibrations produced by the cardiovascular system that are coupled to the precordium can be noninvasively detected using accelerometers. This technique is called seismocardiography. Although clinical applications have been proposed for seismocardiography, the physiology underlying the signal is still not clear. The relationship of seismocardiograms of on the back-to-front axis and cardiac events is fairly well known. However, the three-dimensional6 vibrations detectable with modern accelerometers have not been quantified in terms of cardiac cycle events. A major reason for this might be the degree of inter-subject variability observed in three-dimensional seismocardiograms. We present a method to quantify threedimensional seismocardiography in terms of cardiac cycle events. First, cardiac cycle events are identified from the seismocardiograms and then assigned a number based on the location in which the corresponding event was found. 396 cardiac cycle events from 9 healthy subjec...
Background: Seismocardiography is the noninvasive measurement of cardiac vibrations transmitted t... more Background: Seismocardiography is the noninvasive measurement of cardiac vibrations transmitted to the chest wall by the heart during its movement. While most applications for seismocardiography are based on unidirectional acceleration measurement, several studies have highlighted the importance of three-dimensional measurements in cardiac vibration studies. One of the main challenges in using three-dimensional measurements in seismocardiography is the significant inter-subject variability of waveforms. This study investigates the feasibility of using a unified frame of reference to improve the inter-subject variability of seismocardiographic waveforms. Methods: Three-dimensional seismocardiography signals were acquired from ten healthy subjects to test the feasibility of the present method for improving inter-subject variability of three-dimensional seismocardiograms. The first frame of reference candidate was the orientation of the line connecting the points representing mitral valve closure and aortic valve opening in seismocardiograms. The second candidate was the orientation of the line connecting the two most distant points in the three dimensional seismocardiogram. The unification of the frame of reference was performed by rotating each subject's three-dimensional seismocardiograms so that the lines connecting the desired features were parallel between subjects. Results: The morphology of the three-dimensional seismocardiograms varied strongly from subject to subject. Fixing the frame of reference to the line connecting the MC and AO peaks enhanced the correlation between the subjects in the y axis from 0.42 ± 0.30 to 0.83 ± 0.14. The mean correlation calculated from all axes increased from 0.56 ± 0.26 to 0.71 ± 0.24 using the line connecting the mitral valve closure and aortic valve opening as the frame of reference. When the line connecting the two most distant points was used as a frame of reference, the correlation improved to 0.60 ± 0.22. Conclusions: The results indicate that using a unified frame of reference is a promising method for improving the inter-subject variability of three-dimensional seismocardiograms. Also, it is observed that three-dimensional seismocardiograms seem to have latent inter-subject similarities, which are feasible to be revealed. Because the projections of the cardiac vibrations on the measurement axes differ significantly, it seems obligatory to use three-dimensional measurements when seismocardiogram analysis is based on waveform morphology.
The sensor system presented in this paper utilizes near field imaging for wide area human locatio... more The sensor system presented in this paper utilizes near field imaging for wide area human location and tracking. The sensor system provides reliable location data of humans by measuring slight impedance changes between elements of a thick film sensor matrix under the floor covering. The sensor is completely rigid and undetectable. The low cost and scalable design allows the system to be spread across the whole indoor surface area. The system aims to ensure the efficiency of the elderly care system. Ageing of the population structure in Finland generates an eminent need for more resources in this field. The main pilot sites of the described system are in the senior homes, where the personnel will be most stressed in the near future. The location data can be used for various purposes such as making alarms of senior persons getting up from bed during the night risking them selves of losing balance. Making an alarm during falling down on the floor has an obvious benefit for the habitants of old age homes.
This report illustrates the technical design for the monitoring system of well- being and demonst... more This report illustrates the technical design for the monitoring system of well- being and demonstrates its feasibility in elderly people. The Con-Dis device consists of three buttons with a happy, neutral or unhappy face, each describing the mood of the patient. The functionality of the device was tested on 5 test persons who were asked to demonstrate their state of
In this study, an improved version of the low-frequency indoor location system, with a larger det... more In this study, an improved version of the low-frequency indoor location system, with a larger detection range and more durable antenna laminate, is presented. The basic system uses quad antennas, placed under the floor surface, to locate tags with 125-kHz radio signals. The improvements were achieved with a one-layer laminate construction and transmitter electronics that can feed larger currents to the antennas. The measured tag detection height was 2 m, which is adequate for location applications. The low-frequency signal was not affected by normal objects. The tag location reliability of 96.3% was verified with a practical test. Keywords Indoor location • Low frequency • Near field imaging • Signal penetration 1 Introduction Pervasive and context-aware computing often requires information about the locations and trajectories of people in an indoor environment where GPS, or related positioning, is not available [1]. Applications vary from interactive environments to health care informatics. To satisfy this need, different types of indoor location systems have been created in recent years. The location methods can be roughly divided into active and passive ones. Passive methods observe the person's body itself. This can be done using cameras [2,3], measuring the static [4,5] or dynamic [6] weight distribution, or measuring the body capacitance [7-10]. These methods produce very high tracking accuracies (18-41 cm [3,10,13]); however, no identification takes place. Remote biometric identification with passive methods
In healthcare environment, different kinds of automatic solutions have been created to monitor an... more In healthcare environment, different kinds of automatic solutions have been created to monitor and track patients, for example near-field imaging and low-frequency RFID. The problem has been how to use the context-based data these systems produce and how to show the related information to the nursing staff. This paper shows how hospital data can be automatically transmitted to people using location information. The information is transmitted to a name tag that has wireless connectivity and touch screen with electric paper. This concept is piloted with a test application.
Background: Tomographic imaging has revealed that the body mass index does not give a reliable st... more Background: Tomographic imaging has revealed that the body mass index does not give a reliable state of overall fitness. However, high measurement costs make the tomographic imaging unsuitable for large scale studies or repeated individual use. This paper reports an experimental investigation of a new electromagnetic method and its feasibility for assessing body composition. The method is called body electrical loss analysis (BELA). Methods: The BELA method uses a high-Q parallel resonant circuit to produce a time-varying magnetic field. The Q of the resonator changes when the sample is placed in its coil. This is caused by induced eddy currents in the sample. The new idea in the BELA method is the alter.ed spatial distribution of the electrical losses generated by these currents. The distribution of losses is varied using different excitation frequencies. The feasibility of the method was tested using simplified phantoms. Two of these phantoms were rough estimations of human torso. One had fat in the middle of its volume and saline solution in the outer shell volume. The other had reversed conductivity distributions. The phantoms were placed in the resonator and the change in the losses was measured. Five different excitation frequencies from 100 kHz to 200 kHz were used. Results: The rate of loss as a function of frequency was observed to be approximately three times larger for a phantom with fat in the middle of its volume than for one with fat in its outer shell volume. Conclusions: At higher frequencies the major signal contribution can be shifted toward outer shell volume. This enables probing the conductivity distribution of the subject by weighting outer structural components. The authors expect that the loss changing rate over frequency can be a potential index for body composition analysis.
Medical & Biological Engineering & Computing, 2006
A simple objective screening method for diagnosis of the atrial septal defect (ASD) is needed. Ac... more A simple objective screening method for diagnosis of the atrial septal defect (ASD) is needed. Acoustic signals were collected from 61 children with ASD and 60 with a physiological murmur. The second heart sound (S 2) and the spectrum of systolic murmur were analysed. A statistical model was designed using stepwise logistic regression analysis. Significant variables distinguishing pathological form normal findings were the interval between the first heart sound and the beginning of systolic murmur or the respiratory variation of S 2 , and the frequency of the murmur at its maximum intensity. The area under the ROC curve was 0.922; indicating very good fit of the model and the confidence interval was 0.872-0.971. The sensitivity of the model was 91% and the specificity 73%. The analysis of acoustic findings from the heart is a valuable tool in diagnosing ASD. The next step will be automating this process.
In order to optimize head and neck magnetic resonance (MR) imaging with the spin-lock (SL) techni... more In order to optimize head and neck magnetic resonance (MR) imaging with the spin-lock (SL) technique, the T1ρ relaxation times for normal tissues were determined. Furthermore, T1ρ was compared to T1 and T2 relaxation times. Ten healthy volunteers were studied with a 0.1 T clinical MR imager. T1ρ values were determined by first measuring the tissue signal intensities with different
Aim: To develop an objective diagnostic method that facilitates detection of noncyanotic congenit... more Aim: To develop an objective diagnostic method that facilitates detection of noncyanotic congenital heart diseases.
This paper describes open-source hardware to measure both the magnitude and phase of the electric... more This paper describes open-source hardware to measure both the magnitude and phase of the electrical bioimpedance in a frequency range from few kilohertz up to 100 kHz by using a four-electrode technique. The amount of current injected and the sensitivity of the system can be set to the desired range by changing the front-end resistor values. The system can be easily built and adapted with the help of the design details made available at GitHub. The practical performance was evaluated in abdominal impedance measurement, which was the primary motivation to build the system. Other experiments were performed with a 2R-1C circuit, a 10-Ω resistor, and a 100-nF capacitor, with observed relative errors in the impedances of -0.73 ± 0.34 %, -2.47 ± 1.43 % and -8.81 ± 0.64 % (mean ± SD), respectively, from 10 kHz to 100 kHz.
Ultra-low-field magnetic resonance imaging (ULF MRI) in microtesla fields is a new technology wit... more Ultra-low-field magnetic resonance imaging (ULF MRI) in microtesla fields is a new technology with features unseen in tesla-range MRI. Instead of induction coils as sensors, superconducting quantum interference device (SQUID) sensors are used, providing a frequency-independent signal-to-noise ratio (SNR). Owing to its tolerance for large relative imaging-field inhomogeneities, electromagnet shimming is not necessary. ULF MRI can also be combined with magnetoencephalography (MEG) to image the brain with close to millimetre-millisecond resolution. In this paper, the hybrid MEG-MRI device developed at Aalto University will be presented, as well as a 3D imaging scheme combining gradient-excitation encoding with frequency and phase and encodings. It is noteworthy that, regarding the presented gradient-excitation encoding in ULF MRI, the kilohertz-range Larmor frequencies allow MR signals to propagate unattenuated through tissue, which is not the case in tesla-range MRI with Larmor frequencies even above 100 MHz. Thus, the presented encoding method is especially compatible with ULF MRI, where the use of three different encoding mechanisms for three-dimensional imaging is possible. The feasibility of image reconstruction with the gradient-excitation-encoding method is demonstrated by simulations.
-based evaluation of geometric distortions in functional MRI and diffusion tensor imaging (DTI) w... more -based evaluation of geometric distortions in functional MRI and diffusion tensor imaging (DTI) was investigated. An acrylic water-filled phantom with a grid structure was designed and manufactured to provide accurate geometric information over the volume measured in human brain imaging. The grid structures were well detected in data acquired using a 3-T MRI scanner with echo-planar imaging (EPI) sequences commonly applied in functional MRI and DTI. A method for quantifying distortions in the phantom data was presented and applied for the images. The validity of the phantom for EPI was evaluated by quantitatively comparing the distortions present in and induced by the phantom and a human brain when imaged under identical conditions. The results suggest that the new phantom can reveal geometric distortions easily undermined by standard MRI phantoms. For example, prominent variability in the distortions was found as a function of the orientation of the diffusion-sensitizing gradient. Possible future applications for this type of phantom include quality assurance and calibration of the hardware and software used in EPI-based functional MRI and DTI. Magn Reson Med 57:754-763, 2007.
The present study was designed to evaluate tissue contrast characteristics obtained with the spin... more The present study was designed to evaluate tissue contrast characteristics obtained with the spin-lock (SL) technique by comparing the results with those generated with a magnetization transfer(MT)-weighted gradient echo [GRE, echo-time (TE) ؍ 40 ms] sequence. Twenty-eight patients with hepatic hemangiomas (n ؍ 14), or metastatic liver lesions (n ؍ 14) were imaged at 0.1 T by using identical imaging parameters. Gradient echo, single-slice off-resonance MT, and multiple-slice SL sequences were obtained. SL and MT-effects were measured from the focal liver lesions and from normal liver parenchyma. In addition, tissue contrast values for the liver lesions were determined. Statistically significant difference between the SL-effects of the hemangiomas and metastases, and also between the MT-effects of the lesions was observed (p < 0.02). Tissue contrast values for the lesions proved to be quite similar between the SL and MT techniques. Our results indicate that at 0.1 T multiple-slice SL imaging provides MT based tissue contrast characteristics in tissues rich in protein with good imaging efficiency and wide anatomical coverage, and with reduced motion and susceptibility artifacts.
In this work, novel methods are suggested for assessing signal parameters of the free induction d... more In this work, novel methods are suggested for assessing signal parameters of the free induction decay (FID) in nuclear magnetic resonance (NMR) experiments. The FID signal was recorded in a microtesla field and analysed to determine its relaxation time, amplitude, Larmor frequency and phase. The challenge was posed by the narrow line width, whose related effects were investigated through simulations, also. The developed methods give a new view on FID signal estimation in microtesla as well as lower and higher fields. It is shown that the transverse relaxation time of a sample can be accurately determined in the frequency domain by other means than the Lorentz peak half width. Also, with some realistic approximations, a simple functional form for the power spectrum Lorentz peak shape is proposed. As shown in this work, the inspection of the power spectrum instead of the absorption and dispersion Lorentzians is advantageous in the sense that the waveform is independent of the FID phase. The automatic and efficient methods presented in this work incorporate an integral exponential fit, the fit of the power spectrum Lorentz peak and two ways to determine the FID phase. When there are sufficiently many data points in the Lorentz peak, the power spectrum Lorentz peak shape fit provides a quick, simple and accurate way of determining the amplitude, relaxation time and Larmor frequency of the FID. In the measurements of this work, however, the narrow line width led to establishing a more applicable method which is based on the exponential decay of the Lorentz peak with a temporally moving power spectrum window.
Background: Body electrical loss analysis (BELA) is a new non-invasive way to assess visceral fat... more Background: Body electrical loss analysis (BELA) is a new non-invasive way to assess visceral fat depot size through the use of electromagnetism. BELA has worked well in phantom measurements, but the technology is not yet fully validated. Methods: Ten volunteers (5 men and 5 women, age: 22-60 y, BMI: 21-30 kg/m 2 , waist circumference: 73-108 cm) were measured with the BELA instrument and with cross-sectional magnetic resonance imaging (MRI) at the navel level, navel +5 cm and navel -5 cm. The BELA signal was compared with visceral and subcutaneous fat areas calculated from the MR images. Results: The BELA signal did not correlate with subcutaneous fat area at any level, but correlated significantly with visceral fat area at the navel level and navel +5 cm. The correlation was best at level of navel +5 cm (R 2 = 0.74, P < 0.005, SEE = 29.7 cm 2 , LOOCV = 40.1 cm 2 ), where SEE is the standard error of the estimate and LOOCV is the root mean squared error of leave-one-out style cross-validation. The average estimate of repeatability of the BELA signal observed through the study was ±9.6 %. One of the volunteers had an exceptionally large amount of visceral fat, which was underestimated by BELA. Conclusions: The correlation of the BELA signal with the visceral but not with the subcutaneous fat area as measured by MRI is promising. The lack of correlation with the subcutaneous fat suggests that subcutaneous fat has a minor influence to the BELA signal. Further research will show if it is possible to develop a reliable low-cost method for the assessment of visceral fat either using BELA only or combining it, for example, with bioelectrical impedance measurement. The combination of these measurements may help assessing visceral fat in a large scale of body composition. Before large-scale clinical testing and ROC analysis, the initial BELA instrumentation requires improvements. The accuracy of the present equipment is not sufficient for such new technology. Blomqvist et al. BioMedical Engineering OnLine 2011, 10:98
Background: A simple but countable electronic device has been developed to gain reliable informat... more Background: A simple but countable electronic device has been developed to gain reliable information on elderly patients' perceived well-being. The device has been tested and proven to be technically functional and countable. It was now tested in two care homes for the elderly and two private homes to evaluate if it provided solid information about the well-being of elderly persons. This report illustrates the practical usage of the device and shows its efficiency in gathering solid well-being information from the focus group.
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Papers by Raimo Sepponen