Evaluation of diagnostic accuracy of an oscillometry-based device (VascAssist) combining fully automated ankle-brachial index (ABI) and pulse-wave velocity (PWV) assessment for detection of peripheral arterial disease (PAD).

Magnetic resonance imaging (MRI) has developed dramatically in the 25 years since its clinical introduction. Advances in hardware design have included the development of high field magnets and more sophisticated and sensitive coils. Improvements in sequences, data sampling, and postprocessing software have benefited the attainable spatial and temporal resolution to the point at which the fine depiction of anatomical structure and pathological processes is now routine. As in other radiological areas, the most recent advances in MRI have proven highly valuable in the field of musculoskeletal radiology where the lack of radiation, high soft tissue contrast, and capacity for multiplanar or three-dimensional imaging have made MRI the imaging modality of choice. Particular benefits are seen in diagnostic imaging of the spine where MRI is clearly superior to both conventional radiography and computed tomography. In this article, we discuss the impact of the most recent technological advance in MRI, namely the advent of 3 Tesla (3-T) imaging, on diagnostic imaging of the spine. Comparisons are drawn with imaging at 1.5 T, and emphasis is placed on MR physics and on the benefits and principal difficulties associated with spine imaging at high field strength.

Objectives: The aim of this study was to evaluate lesion enhancement (LE) and contrast-to-noise ratio (CNR) properties of P846, a new intermediate sized, high relaxivity Gd-based contrast agent at 3 Tesla in a rat brain glioma model, and to compare this contrast agent with a high relaxivity, macromolecular compound (P792), and a standard extracellular Gd-chelate (Gd-DOTA). Materials and Methods: Seven rats with experimental induced brain glioma were evaluated using 3 different contrast agents, with each MR examination separated by at least 24 hours. The time between injections assured sufficient clearance of the agent from the tumor, before the next examination. P792 (Gadomelitol, Guerbet, France) and P846 (a new compound from Guerbet Research) are macromolecular and high relaxivity contrast agents with no protein binding, and were compared with the extracellular agent Gd-DOTA (Dotarem, Guerbet, France). T1w gradient echo sequences (TR/TE 200 milliseconds/7.38 milliseconds, flip angle = 90°, acquisition time: 1:42 minutes:sec, voxel size: 0.2 × 0.2 × 2.0 mm³, FOV = 40 mm, acquisition matrix: 256 × 256) were acquired before and at 5 consecutive time points after each intravenous contrast injection in the identical slice orientation, using a dedicated 4-channel head array animal coil. The order of contrast media injection was randomized, with however Gd-DOTA used either as the first or second contrast agent. Contrast agent dose was adjusted to compensate for the different T1 relaxivities of the 3 agents. Signal-to-noise ratio, CNR, and LE were evaluated using region-of-interest analysis. A veterinary histopathologist confirmed the presence of a glioma in each subject, after completion of the imaging study. Results: P792 showed significantly less LE as compared with Gd-DOTA within the first 7 minutes after contrast agent injection (P < 0.05) with, however, reaching comparable LE values at 9 minutes after injection (P = 0.07). However, P792 provided significantly less CNR as compared with Gd-DOTA (P < 0.05) for all examination time points. P846 provided comparable but persistent LE as compared with Gd-DOTA (P < 0.05) and demonstrated significantly greater LE and CNR when compared with P792 (P < 0.05). No statistically significant differences between CNR values for Gd-DOTA and P846 were noted for all examination time points (P < 0.05), with P846 administered at one-fourth the dose as compared with Gd-DOTA. Conclusion: The intravascular contrast medium P792 showed significantly less LE and CNR in comparison to Gd-DOTA and P846, suggesting that it does not show marked extravasation from tumor neocapillaries and does not significantly cross the disrupted blood brain-barrier in this rat glioma model. In distinction, P846 provides comparable enhancement properties at a field strength of 3 Tesla to the extracellular contrast agent Gd-DOTA, using the adjusted dose, suggesting that it crosses the disrupted blood-brain-barrier and tumor capillaries, most likely based on the decreased molecular weight as compared with P792. At the same time, the high relaxivity of this compound allows for decreasing the injected gadolinium dose by a factor of 4 whereas providing comparable enhancement properties when compared with a standard extracellular Gd-chelate (Gd-DOTA) at a dose of 0.1 mmol/kg body weight.

This study aims to compare the enhancement properties of an experimental high-relaxivity extracellular gadolinium chelate (P03277) with a standard extracellular contrast agent (gadobutrol) in vivo in a rat model of hepatic colorectal cancer metastases and in vitro by relaxometry measurements. Ten rats with hepatic colorectal cancer metastases were examined using a 9.4 T animal scanner (Bruker, Germany). Each animal was subjected to 2 contrast-enhanced magnetic resonance imaging experiments separated by 2 days receiving 0.1 mmol/kg body weight gadobutrol and 0.1 mmol/kg body weight P03277 intravenously in a random manner. T1-weighted self-gated fast low-angle shot sequences (time to repetition/time to echo, 45/2.5 milliseconds; flip angle, 45 degrees; acquisition time, 1:23 minutes; voxel size, 0.2 × 0.2 × 1.0 mm) were acquired before and at 10 consecutive time points after contrast injection. We assessed signal-to-noise ratio (SNR) of tumor (SNRtumor) and normal liver tissue (SNRliver), contrast-to-noise ratio, and lesion enhancement (LE). In addition, relaxation rates of P03277 and gadobutrol were assessed in vitro in human plasma at 37°C at a field strength of 9.4 T.Statistical analyses included paired t tests and Wilcoxon matched pairs signed rank tests. SNRliver, SNRtumor, contrast-to-noise ratio, and LE were significantly higher (P < 0.05) using P03277 for all time points as compared with gadobutrol. Both agents demonstrated comparable contrast kinetics with an early peak enhancement immediately after application (initial percent LE: gadobutrol, 84%; P03277, 156%) and an early and continuous washout during the examination period (final percent LE: gadobutrol, 36%; P03277, 63%). In vitro evaluation of relaxivities demonstrated markedly higher R1 for P03277 (8.6 mM s) as compared with gadobutrol (4.2 mM s). This study provides the first in vivo and in vitro data of P03277, an experimental extracellular MR contrast agent. P03277 demonstrates significantly better enhancement properties as compared with gadobutrol in experimental hepatic colorectal cancer metastases. In addition, in vitro data demonstrate superior relaxivities of P03277 at a broad spectrum of different field strengths. Hence, this new agent has the potential to improve lesion conspicuity and subsequently sensitivity in diagnostic imaging for both clinical magnetic resonance imaging at 1.5 or 3 T and ultra-high field applications between 4.7 and 9.4 T.

A critical problem in cardiovascular MRI in small rodents is adjusting the sequence acquisition to the high heart and respiratory rates. The aim of this study was to compare a retrospectively self-gated fast low angle shot navigator (RSG-FLASH) sequence with a conventional prospectively triggered (PT-FLASH) sequence for cine imaging of the ascending aorta in mice at 9.4 T. Ten C57/BL6 mice were examined with a horizontal bore 9.4 Tesla MRI animal scanner using a dedicated 2 × 2 phased-array surface coil. We acquired a RSG-FLASH sequence (RSG-FLASH sequences (repetition time (TR) / echo time (TE) = 6.5/2.5 ms, flip angle (FA) = 10 degrees, field of view (FOV) = 2 × 2 cm, matrix = 384 × 384, slice thickness = 1 mm, 25 movie frames) perpendicular to the ascending aorta using the IntraGate technique. At the same position, we performed a PT-FLASH sequence (TR/TE = 6.5/2.1 ms, FA = 10 degrees, FOV = 2 × 2 cm, matrix = 384 × 384, slice thickness = 1 mm) in which the maximum number of movie frames had to be adjusted to the interval between two R-peaks (RR interval) of the electrocardiogram (ECG) with: number of frames = RR interval / TR." Cross-sectional vessel areas at end-systole (AES) and end-diastole (AED) were measured to determine the aortic strain (ΔA = (AES-AED)/AED). Two blinded readers rated the sequences for presence of flow and trigger artifacts and their influence on the depiction of the blood/vessel-wall interface. Irregularities in displaying the cardiac cycle and the overall suitability of the sequence for aortic strain evaluation were assessed using a 5-level ordinal scale. Statistical differences were analyzed using Student t test and Wilcoxon signed rank test (P < 0.05). Intra- and interobserver variability was evaluated using Bland-Altman analyses. No significant differences were noted between techniques regarding the measured vessel areas (AED: P = 0.07, AES: P = 0.34), ΔA: P = 0.1). Similarly, there were no significant differences in heart (P = 0.06) and respiratory (P = 0.24) rates. The acquisition time for RSG-FLASH sequence was significantly shorter (P = 0.04). Significantly fewer flow and trigger artifacts were noted by both readers with the RSG-FLASH sequence. Likewise, both readers considered the RSG-FLASH sequence to be superior for depiction of the blood/vessel-wall interface. The RSG-FLASH sequence was also rated superior regarding irregularities in displaying the cardiac cycle and in terms of overall suitability for evaluation of AED, AES, and aortic strain (P < 0.05 each). RSG-FLASH is preferable for cine imaging of the aorta. It provides the same quantitative data as PT-FLASH cine imaging but is less prone to flow and trigger artifacts. RSG-FLASH permits more homogeneous depiction of the cardiac cycle and is faster than the PT-FLASH sequence. PT-FLASH is more prone to misregistration of the respiratory cycle or the ECG by the external monitoring device used for acquisition. This effect may be even more pronounced in animals with disease models that are less stable in terms of heart and respiration rate during anesthesia.