DWI-based neural fingerprinting technology: a preliminary study on stroke analysis.

Stroke is a common neural disorder in neurology clinics. Magnetic resonance imaging (MRI) has become an important tool to assess the neural physiological changes under stroke, such as diffusion weighted imaging (DWI) and diffusion tensor imaging (DTI). Quantitative analysis of MRI images would help medical doctors to localize the stroke area in the diagnosis in terms of structural information and physiological characterization. However, current quantitative approaches can only provide localization of the disorder rather than measure physiological variation of subtypes of ischemic stroke. In the current study, we hypothesize that each kind of neural disorder would have its unique physiological characteristics, which could be reflected by DWI images on different gradients. Based on this hypothesis, a DWI-based neural fingerprinting technology was proposed to classify subtypes of ischemic stroke. The neural fingerprint was constructed by the signal intensity of the region of interest (ROI) on the DWI images under different gradients. The fingerprint derived from the manually drawn ROI could classify the subtypes with accuracy 100%. However, the classification accuracy was worse when using semiautomatic and automatic method in ROI segmentation. The preliminary results showed promising potential of DWI-based neural fingerprinting technology in stroke subtype classification. Further studies will be carried out for enhancing the fingerprinting accuracy and its application in other clinical practices.

A blood pressure monitoring method for stroke management.

Blood pressure is one important risk factor for stroke prognosis. Therefore, continuous monitoring of blood pressure is crucial for preventing and predicting stroke. However, current blood pressure devices are mainly air-cuff based, which only can provide measurements intermittently. This study proposed a new blood pressure estimation method based on the pulse transit time to realize continuous monitoring. The proposed method integrated a linear model with a compensation algorithm. A calibration method was further developed to guarantee that the model was personalized for individuals. Variation and variability of pulse transit time were introduced to construct the compensation algorithm in the model. The proposed method was validated by the data collected from 30 healthy subjects, aged from 23 to 25 years old. By comparing the estimated value to the measurement from an oscillometry, the result showed that the mean error of the estimated blood pressure was -0.2 ± 2.4 mmHg and 0.5 ± 3.9 mmHg for systolic and diastolic blood pressure, respectively. In addition, the estimation performance of the proposed model is better than the linear model, especially for the diastolic blood pressure. The results indicate that the proposed method has promising potential to realize continuous blood pressure measurement.

Muscle-based pharmacokinetic modeling of marrow perfusion for osteoporotic bone in females.

The pharmacokinetic model has been widely used in tissue perfusion analysis, such as bone marrow perfusion. In the modeling process, the arterial input function is important to guarantee the reliability of the fitting result. However, the arterial input function is variable and hard to control, which makes it difficult to compare results across different studies. The purpose of this study was to establish a muscle-based pharmacokinetic model for bone marrow perfusion without using arterial input function. Erector spinae muscle around the vertebral body was selected as the reference region. The study was carried out in elderly females with different bone mineral densities (normal, osteopenia, and osteoporosis). Quantitative parameters were extracted from the pharmacokinetic model. Parameter K (trans,BM) (contrast agent extravasation rate constants for blood perfusion of the bone marrow) showed a significant reduction in subjects with lower bone mineral density, which is consistent with previous studies. However, muscle perfusion parameters remained unchanged among different groups. The results indicated that the muscle-based model was stable for bone marrow perfusion modeling. Additionally, nonsignificant change in muscle parameters indicated that the diminished perfusion is only a local rather than a systematic change in the bone marrow for osteoporosis.

Cramér-Rao bound for Intravoxel Incoherent Motion Diffusion Weighted Imaging fitting.

The precision of parameter estimation for Intravoxel Incoherent Motion Diffusion Weighted Imaging (IVIM-DWI) was investigated by examining their Cramér-Rao bounds (CRBs) under the presence of Rician noise. Monte Carlo (MC) simulation was also conducted to validate the CRB results. The estimation uncertainties of true diffusion coefficient (D) and perfusion fraction (f0) could reach 3.89% and 11.65% respectively with typical parameter values at a moderate signal-to-noise ratio (SNR) of 40. However, to estimate pseudo diffusion coefficient (D*) within 10% uncertainty requires SNR>122. The results also showed that the estimation precision of each parameter is not only dependent on SNR but also their true values, while this mutual dependency is complicated. Under some particular cases, estimation uncertainty for certain parameters might be smaller than 5% at a moderate SNR of 40. However, the simultaneous precise estimation for all three parameters is theoretically difficult and highly SNR demanding.

Bone marrow fat content in the elderly: a reversal of sex difference seen in younger subjects.

PURPOSE: To investigate vertebral bone marrow fat content in elderly subjects related to sex, age, and bone mineral density (BMD) and relate these findings to published data in younger subjects. MATERIALS AND METHODS: A total of 259 healthy subjects (145 females, 114 males; age range, 62-90 years) underwent proton ((1) H) MR spectroscopy of L3 vertebral body and BMD of the lumbar spine with results stratified according to age. Ninety age- and BMD-matched subjects were selected to determine sex differences in marrow fat content and BMD. RESULTS: In females, vertebral marrow fat content rose sharply between 55 and 65 years of age while in males vertebral marrow fat content rose gradually throughout life. Vertebral marrow fat content in females more than 60 years was approximately 10% higher in females than males, i.e., a reversal of sex difference reported in marrow fat content for subjects less than 60 years. CONCLUSION: Marrow fat content increases sharply in female subjects between 55 and 65 years of age while male subjects continue to increase marrow fat at a more gradual steady rate. Females older than 60 years have a higher marrow fat content than males. This increased deposition in marrow fat concurs with recognized changes in extraosseous fat distribution in postmenopausal females.

Modified brix model analysis of bone perfusion in subjects of varying bone mineral density.

PURPOSE: To apply pharmacokinetic modeling to the investigation of bone perfusion in subjects of varying bone mineral density. MATERIALS AND METHODS: This study re-analyzed previous experimental data. A modified pharmacokinetic model was applied to data obtained from two prior studies of dynamic contrast-enhanced MR imaging of L3 vertebral body in 165 subjects (65 males, 100 females), classified into three groups (normal, osteopenia, and osteoporosis) according to bone mineral density. Three parameters, amplitude A, exchange rate (k(ep)), and elimination rate (k(el)), were obtained by fitting the signal intensity to the pharmacokinetic model. These parameters were compared across the three groups for males and females, respectively. RESULTS: Perfusion parameters, amplitude A was found to be reduced in osteoporotic subjects with additional, though less pronounced, reductions found in the permeability constant (A*k(ep)) and the elimination rate (k(el)). Increased marrow fat content was found in osteoporotic bone, which helped to partially explain the observed reduction in interstitial space. CONCLUSION: By pharmacokinetic model, bone perfusion can be quantitatively analyzed with alteration in functional parameters related to microcirculation in subjects of varying bone mineral density. Developing bone marrow specific pharmacokinetic models should help to deepen knowledge of physiological and pathological perfusion changes occurring in bone.

Kinematics of the lumbar spine in elderly subjects with decreased bone mineral density.

Lumbar spine kinematics was studied in subjects with normal bone mineral density, osteopenia and osteoporosis to determine the effect of bone mineral density and morphology on the flexion-extension movement patterns of the lumbar spine. Lateral radiographs and skin-mounted electromagnetic motion tracking sensors were employed to study lumbar spine kinematics using a Bayesian Belief Network model. The predicted angular displacement of the vertebrae had a high correlation (r = 0.91, p < 0.001) with the actual movements. The overall mean error was -0.51 degrees +/- 3.11 degrees. Intervertebral angular displacement and velocity consistently increased from L1/L2 to L5/S1. Differences were observed in the movement pattern between normal subjects and those with decreased bone density. In normal subjects, vertebral angular acceleration consistently decreased from the upper to the lower vertebrae but the same consistent predictable pattern was not observed in the subjects with decreased bone mineral density. It is possible that these changes in kinematic behaviours are related to morphological changes as well as altered neuromuscular functions.

A new method for determining lumbar spine motion using Bayesian belief network.

A Bayesian network dynamic model was developed to determine the kinematics of the intervertebral joints of the lumbar spine. Radiographic images in flexion and extension postures were used as input data for modeling, together with movement information from the skin surface using an electromagnetic motion tracking system. Intervertebral joint movements were then estimated by the graphic network. The validity of the model was tested by comparing the predicted position of the vertebrae in the neutral position with those obtained from the radiographic image in the neutral posture. The correlation between the measured and predicted movements was 0.99 (p<0.01) with a mean error of less than 1.5 degrees. The movement sequence of the various vertebrae was examined based on the model output, and wide variations in the kinematic patterns were observed. The technique is non-invasive and has potential to be used clinically to measure the kinematics of lumbar intervertebral movement.

Error analysis on spinal motion measurement using skin mounted sensors.

Measurement errors of skin-mounted sensors in measuring forward bending movement of the lumbar spines are investigated. In this investigation, radiographic images capturing the entire lumbar spines' positions were acquired and used as a 'gold' standard. Seventeen young male volunteers (21 (SD 1) years old) agreed to participate in the study. Light-weight miniature sensors of the electromagnetic tracking systems-Fastrak were attached to the skin overlying the spinous processes of the lumbar spine. With the sensors attached, the subjects were requested to take lateral radiographs in two postures: neutral upright and full flexion. The ranges of motions of lumbar spine were calculated from two sets of digitized data: the bony markers of vertebral bodies and the sensors and compared. The differences between the two sets of results were then analyzed. The relative movement between sensor and vertebrae was decomposed into sensor sliding and titling, from which sliding error and titling error were introduced. Gross motion range of forward bending of lumbar spine measured from bony markers of vertebrae is 67.8 degrees (SD 10.6 degrees ) and that from sensors is 62.8 degrees (SD 12.8 degrees ). The error and absolute error for gross motion range were 5.0 degrees (SD 7.2 degrees ) and 7.7 degrees (SD 3.9 degrees ). The contributions of sensors placed on S1 and L1 to the absolute error were 3.9 degrees (SD 2.9 degrees ) and 4.4 degrees (SD 2.8 degrees ), respectively.