Hsu-Hsia Peng

Quantification of the pulse wave velocity of the descending aorta using axial velocity profiles from phase-contrast magnetic resonance imaging

The pulse wave velocity (PWV) of aortic blood flow is considered a surrogate for aortic compliance. A new method using phase‐contrast (PC)‐MRI is presented whereby the spatial and temporal profiles of axial velocity along the descending aorta can be analyzed. Seventeen young healthy volunteers (the YH group), six older healthy volunteers (the OH group), and six patients with coronary artery disease (the CAD group) were studied. PC‐MRI covering the whole descending aorta was acquired, with velocity gradients encoding the in‐plane velocity. From the corrected axial flow velocity profiles, PWV was determined from the slope of an intersecting line between the presystolic and early systolic phases. Furthermore, the aortic elastic modulus (Ep) was derived from the ratio of the brachial pulse pressure to the strain of the aortic diameter. The PWV increased from YH to OH to CAD (541 ± 94, 808 ± 184, 1121 ± 218 cm/s, respectively; P = 0.015 between YH and OH; P = 0.023 between OH and CAD). There was a high correlation between PWV and Ep (r = 0.861, P < 0.001). Multivariate analysis showed that age and CAD were independent risk factors for an increase in the PWV. Compared to existing methods, our method requires fewer assumptions and provides a more intuitive and objective way to estimate the PWV. Magn Reson Med, 2006.

Inter-Strain Differences in Default Mode Network: A Resting State fMRI Study on Spontaneously Hypertensive Rat and Wistar Kyoto Rat.

Genetic divergences among mammalian strains are presented phenotypically in various aspects of physical appearance such as body shape and facial features. Yet how genetic diversity is expressed in brain function still remains unclear. Functional connectivity has been shown to be a valuable approach in characterizing the relationship between brain functions and behaviors. Alterations in the brain default mode network (DMN) have been found in human neuropsychological disorders. In this study we selected the spontaneously hypertensive rat (SHR) and the Wistar Kyoto rat (WKY), two inbred rat strains with close genetic origins, to investigate variations in the DMN. Our results showed that the major DMN differences are the activities in hippocampal area and caudate putamen region. This may be correlated to the hyperactive behavior of the SHR strain. Advanced animal model studies on variations in the DMN may have potential to shed new light on translational medicine, especially with regard to neuropsychological disorders.

Simultaneous Temperature and Magnetization Transfer (MT) Monitoring During High-Intensity Focused Ultrasound (HIFU) Treatment: Preliminary Investigation on Ex Vivo Porcine Muscle

To measure temperature change and magnetization transfer ratio (MTR) simultaneously during high‐intensity focused ultrasound (HIFU) treatment.

Water signal attenuation by D2O infusion as a novel contrast mechanism for 1H perfusion MRI.

Deuterium oxide (D2O), which is commercially available and nonradioactive, was proposed as a perfusion tracer before the clinical usage of conventional gadolinium‐based MRI contrast agents. However, the sensitivity of direct deuterium detection is the major challenge for its application. In this study, we propose a contrast‐enhanced strategy to indirectly trace administered D2O by monitoring the signal attenuation of 1H MRI. Experiments on D2O concentration phantoms and in vivo rat brains were conducted to prove the concept of the proposed contrast mechanism. An average maximum signal drop ratio of 5.25 ± 0.91% was detected on 1H MR images of rat brains with 2 mL of D2O administered per 100 g of body weight. As a diffusible tracer for perfusion, D2O infusion is a practicable method for the assessment of tissue perfusion and has the potential to provide different information from gadolinium‐based contrast agents, which have limited permeability for blood vessels. Furthermore, the observed negative relaxivities of D2O reveal the 1H–D exchange effect. Therefore, applications of perfusion MRI with D2O as a contrast agent are worthy of further investigation. Copyright

Left cervical aortic arch with aneurysm and obstruction: three-dimensional computed tomographic angiography and magnetic resonance angiographic appearance.

Cervical arch is a rare congenital anomaly presumed to result from persistence of the third aortic arch and regression of the normal fourth arch. Rather rare is cervical aortic arch associated with aneurysm and obstruction, with eight known cases reported. Definitive diagnosis with a noninvasive imaging modality is desirable and very important to prevent the need for disaster intervention. We present two cases of a pulsatile mass in the left supraclavicular region. Three-dimensional computed tomographic angiography and magnetic resonance angiography clearly showed a left-sided cervical aortic arch (Haughton type D) with arch aneurysm and coarctation (pseudocoarctation).

Left ventricular regional myocardial motion and twist function in repaired tetralogy of Fallot evaluated by magnetic resonance tissue phase mapping

ObjectivesWe aimed to characterise regional myocardial motion and twist function in the left ventricles (LV) in patients with repaired tetralogy of Fallot (rTOF) and preserved LV global function.MethodsWe recruited 47 rTOF patients and 38 age-matched normal volunteers. Tissue phase mapping (TPM) was performed for evaluating the LV myocardial velocity in longitudinal, radial, and circumferential (Vz, Vr, and VØ) directions in basal, middle, and apical slices. The VØ peak-to-peak (PTP) during systolic phases, the rotation angle of each slice, and VØ inconsistency were computed for evaluating LV twist function and VØ dyssynchrony.ResultsAs compared to the controls, the rTOF patients presented decreased RV ejection fraction (RVEF) (p = 0.002) and preserved global LV ejection fraction (LVEF). They also demonstrated decreased systolic and diastolic Vz in several LV segments and higher diastolic Vr in the septum (all p < 0.05). A lower VØ PTP, higher VØ inconsistency, and reduced peak net rotation angle (all p < 0.05) were observed. The aforementioned indices demonstrated an altered LV twist function in rTOF patients in an early disease stage.ConclusionsMR TPM could provide information about early abnormalities of LV regional motion and twist function in rTOF patients with preserved LV global function.Key points• Patients with rTOF presented significantly reduced systolic and diastolic Vz in the LV.• rTOF patients demonstrated significantly increased diastolic Vr in the septum.• Abnormal characteristics of the segmental dynamic velocity evolution were shown in rTOF.• rTOF patients presented altered circumferential rotation and velocity inconsistency in early stage.

Real-time monitoring of inertial cavitation effects of microbubbles by using MRI: In vitro experiments

To investigate the feasibility of half‐Fourier acquisition single‐shot turbo spin‐echo (HASTE) for real‐time monitoring of signal changes because of water flow induced by inertial cavitation (IC) during microbubbles (MBs)‐present focused ultrasound (FUS) exposure.

Proton Resonance Frequency Shift-Weighted Imaging for Monitoring MR-Guided High-Intensity Focused Ultrasound Transmissions

To combine temperature‐related information of phase images and magnitude images acquired from an MR spoiled gradient echo sequence using a postprocessing method referred to as PRF‐shift‐weighted imaging (PRFSWI).

Using microbubbles as an MRI contrast agent for the measurement of cerebral blood volume

The susceptibility differences at the gas–liquid interface of microbubbles (MBs) allow their use as an intravascular susceptibility contrast agent for in vivo MRI. However, the characteristics of MBs are very different from those of the standard gadolinium‐diethylenetriaminepentaacetic acid (Gd‐DPTA) contrast agent, including the size distribution and hemodynamic properties, which could influence MRI outcomes. Here, we investigate quantitatively the correlation between the relative cerebral blood volume (rCBV) derived from Gd‐DTPA (rCBVGd) and the MB‐induced susceptibility effect (ΔR2*MB) by conventional dynamic susceptibility contrast MRI (DSC‐MRI). Custom‐made MBs had a mean diameter of 0.92 µm and were capable of inducing 4.68 ± 3.02% of the maximum signal change (MSC). The MB‐associated ΔR2*MB was compared with rCBVGd in 16 rats on 4.7‐T MRI. We observed a significant effect of the time to peak (TTP) on the correlation between ΔR2*MB and rCBVGd, and also found a noticeable dependence between TTP and MSC. Our findings suggest that MBs with longer TTPs can be used for the estimation of rCBV by DSC‐MRI, and emphasize the critical effect of TTP on MB‐based contrast MRI. Copyright

Letter to the editor re: Assessment of the spatial pattern of colorectal tumour perfusion estimated at perfusion CT using two-dimensional fractal analysis.

Dear Editor: A recent electronic publication in European Radiology documented the use of two-dimensional fractal analysis applied to perfusion CT images to assess the spatial pattern of colorectal adenocarcinoma [1]. In addition to reporting the value of the commonly assessed fractal dimension to the differentiation of colorectal cancer from the controls, the authors also described a new parameter, namely the fractal abundance, to potentially assist the fractal dimension as an adjunct to characterize lesion morphology. Results show that the fractal abundance values are significantly higher for the colorectal cancer lesions as compared with normal sigmoid colon, no matter what the tissue outline, the isolated low perfusion area, or the isolated high perfusion area. We would like to provide a different yet intuitive interpretation to the findings stated above regarding the fractal abundance. In the article by Goh et al. [1], fractal analysis was performed using a box counting algorithm, where the number of boxes containing a certain part of the lesion (NL) is counted as a function of the box size L, with the relationship given by