Effect of temporal sampling protocols on myocardial blood flow measurements using Rubidium-82 PET

Background A variety of temporal sampling protocols is used worldwide to measure myocardial blood flow (MBF). Both the length and number of time frames in these protocols may alter MBF and myocardial flow reserve (MFR) measurements. We aimed to assess the effect of different clinically used temporal sampling protocols on MBF and MFR quantification in Rubidium-82 (Rb-82) PET imaging. Methods We retrospectively included 20 patients referred for myocardial perfusion imaging using Rb-82 PET. A literature search was performed to identify appropriate sampling protocols. PET data were reconstructed using 14 selected temporal sampling protocols with time frames of 5-10 seconds in the first-pass phase and 30-120 seconds in the tissue phase. Rest and stress MBF and MFR were calculated for all protocols and compared to the reference protocol with 26 time frames. Results MBF measurements differed (P ≤ 0.003) in six (43%) protocols in comparison to the reference protocol, with mean absolute relative differences up to 16% (range 5%-31%). Statistically significant differences were most frequently found for protocols with tissue phase time frames < 90 seconds. MFR did not differ (P ≥ 0.11) for any of the protocols. Conclusions Various temporal sampling protocols result in different MBF values using Rb-82 PET. MFR measurements were more robust to different temporal sampling protocols.

A 4D continuous representation of myocardial velocity fields from tissue phase mapping magnetic resonance imaging

Myocardial velocities carry important diagnostic information in a range of cardiac diseases, and play an important role in diagnosing and grading left ventricular diastolic dysfunction. Tissue Phase Mapping (TPM) Magnetic Resonance Imaging (MRI) enables discrete sampling of the myocardium’s underlying smooth and continuous velocity field. This paper presents a post-processing framework for constructing a spatially and temporally smooth and continuous representation of the myocardium’s velocity field from TPM data. In the proposed scheme, the velocity field is represented through either linear or cubic B-spline basis functions. The framework facilitates both interpolation and noise reducing approximation. As a proof-of-concept, the framework was evaluated using artificially noisy (i.e., synthetic) velocity fields created by adding different levels of noise to an original TPM data. The framework’s ability to restore the original velocity field was investigated using Bland-Altman statistics. Moreover, we calculated myocardial material point trajectories through temporal integration of the original and synthetic fields. The effect of noise reduction on the calculated trajectories was investigated by assessing the distance between the start and end position of material points after one complete cardiac cycle (end point error). We found that the Bland-Altman limits of agreement between the original and the synthetic velocity fields were reduced after application of the framework. Furthermore, the integrated trajectories exhibited consistently lower end point error. These results suggest that the proposed method generates a realistic continuous representation of myocardial velocity fields from noisy and discrete TPM data. Linear B-splines resulted in narrower limits of agreement between the original and synthetic fields, compared to Cubic B-splines. The end point errors were also consistently lower for Linear B-splines than for cubic. Linear B-splines therefore appear to be more suitable for TPM data.

Microstructure and Materials Properties of Understoichiometric TiBx Thin Films Grown by HiPIMS

<p>In the present research article we report synthesis of TiB_x, 1.43<i>n-situ</i> mass- and energy-spectroscopy is used to explain the obtained compositional range. Excess B in overstoichiometric TiB<i>_x</i>thin films from DCMS results in a hardness up to 37.7±0.8 GPa, attributed to the formation of an amorphous B-rich tissue phase separating stoichiometric TiB₂ columnar structures. With a particular focus on characterization of the understoichiometric samples, we show that understoichiometric TiB_1.43 thin films synthesized by HiPIMS exhibit a superior hardness of 43.9±0.9 GPa, where the deficiency of B is found to be accommodated by Ti planar defects. The apparent fracture toughness, electrical resistivity and thermal conductivity of the same sample is 4.2±0.1 MPa√m, 367±7 μΩ·cm and 5.1 W/(m.K), respectively, as compared to corresponding values for overstoichiometric TiB_2.20 DCMS thin film samples of 3.2±0.1 MPa√m, 309±4 μΩ·cm and 3.0 W/(m.K). </p>

Microstructure and Materials Properties of Understoichiometric TiBx Thin Films Grown by HiPIMS

<p>In the present research article we report synthesis of TiB_x, 1.43<i>n-situ</i> mass- and energy-spectroscopy is used to explain the obtained compositional range. Excess B in overstoichiometric TiB<i>_x</i>thin films from DCMS results in a hardness up to 37.7±0.8 GPa, attributed to the formation of an amorphous B-rich tissue phase separating stoichiometric TiB₂ columnar structures. With a particular focus on characterization of the understoichiometric samples, we show that understoichiometric TiB_1.43 thin films synthesized by HiPIMS exhibit a superior hardness of 43.9±0.9 GPa, where the deficiency of B is found to be accommodated by Ti planar defects. The apparent fracture toughness, electrical resistivity and thermal conductivity of the same sample is 4.2±0.1 MPa√m, 367±7 μΩ·cm and 5.1 W/(m.K), respectively, as compared to corresponding values for overstoichiometric TiB_2.20 DCMS thin film samples of 3.2±0.1 MPa√m, 309±4 μΩ·cm and 3.0 W/(m.K). </p>

Feasibility of dual phase 99mTc-MDP SPECT/CT imaging in rheumatoid arthritis evaluation

ObjectivesTo prospectively demonstrate the feasibility of performing dual-phase SPECT/CT for the assessment of the small joints of the hands of rheumatoid arthritis (RA) patients, and to evaluate the reliability of the quantitative and qualitative measures derived from the resulting images.MethodsA SPECT/CT imaging protocol was developed in this pilot study to scan both hands simultaneously in RA patients, in two phases of 99mTc-MDP radiotracer uptake; namely the soft-tissue blood pool phase (within 15 minutes after radiotracer injection) and osseous phase (after 3 hours). Joints were evaluated qualitatively (normal vs. abnormal uptake) and quantitatively (by measuring the maximum corrected count ratio [MCCR]). Qualitative and quantitative evaluations were repeated to assess reliability.ResultsFour participants completed seven studies (all four were imaged at baseline, and three of them at follow-up after 1-month of arthritis therapy). A total of 280 joints (20 per hand) were evaluated. The MCCR from soft-tissue phase scans was significantly higher for clinically abnormal joints compared to clinically normal ones; p<0.001, however the MCCR from the osseous phase scans were not different between the two groups. Intraclass Correlation Coefficient (ICC) for MCCR was excellent (0.9789, 95% confidence interval [CI]: 0.9734-0.9833). Intra-observer agreement for qualitative SPECT findings was good for both the soft-tissue phase (kappa=0.78, 95%CI: 0.72-0.83) and osseous-phase (kappa=0.70, 95%CI: 0.64-0.76) scans.ConclusionExtracting reliable quantitative and qualitative measures from dual-phase 99mTc-MDP SPECT/CT hand scans is feasible in RA patients. SPECT/CT may provide a unique means for assessing both synovitis and osseous involvement in RA joints using the same radiotracer injection.