卷 47, 编号 8 (2016)

To evaluate the clinical potential of a non-contrast-enhanced magnetic resonance angiography (NCE-MRA) technique using flow-sensitive dephasing (FSD)-prepared steady-state free precession (SSFP), FSD-NCE-MRA, for hand arterial angiography in patients with rheumatoid arthritis. Twenty-four patients were recruited and underwent FSD-NCE-MRA on a 1.5T MR system. For comparison, conventional dynamic CE-MRA was also conducted after the FSD-NCE-MRA scan. Images obtained by both FSD-NCE-MRA and CE-MRA were independently evaluated by two experienced radiologists using a four-point scale and the hand arteries were divided into wrist, palm and finger segments for image quality assessment. Signal-to-noise ratio (SNR), artery-to-muscle contrast-to-noise ratio (CNR), and vessel sharpness of superficial/deep palmar arch and common digital artery were also measured by a physician. Experimental results demonstrated that FSD-NCE-MRA yielded a higher percentage of diagnostic value arterial segments than CE-MRA (96 vs. 83 %, P < 0.05). Besides, average SNR, CNR, and vessel sharpness were also higher on FSD-NCE-MRA images than CE-MRA ones (SNR: 57 ± 13 vs. 15 ± 4; CNR: 54 ± 13 vs. 13 ± 4; sharpness: 1.1 ± 0.1 vs. 0.9 ± 0.1; all P < 0.05). Thus, FSD-NCE-MRA allows a higher image quality in the depiction of the hand arterial tree for the patients with rheumatoid arthritis compared to CE-MRA. The technique, FSD-NCE-MRA, may be a safe and improved clinical screening tool for the assessment of the hand arteries in rheumatoid arthritis patients without using any contrast agents.

The magnetic properties of novel liquid-crystalline dendrimeric iron(III) complexes of the first generation, [Fe(L₂)]⁺X⁻, where L = 3,4,5-tri(tetradecyloxy) benzoyloxy-4-salicyliden-N′-ethyl-N-ethylenediamine and X = Cl, NO₃ have been investigated for the first time by electron paramagnetic resonance (EPR) and Mössbauer spectroscopy in the wide (4–300 K) temperature range. It has been shown that each compound consists of two types of iron centers: low-spin (LS, S = 1/2) and high-spin (HS, S = 5/2). A partial thermally driven spin transition (S = 5/2 ↔ 1/2) was observed in these complexes. EPR showed that the LS and HS iron centers are coupled by weak antiferromagnetic interactions and most probably form a chain in the column. Mössbauer spectroscopy confirmed the existence of the LS and HS Fe(III) centers in the compounds, a partial spin crossover of approximately 2–8 % of the Fe(III) molecules and showed that the HS Fe(III) centers demonstrate the antiferromagnetc type of ordering at 5 K.

This study proposes a robust method for signal-to-noise ratio (SNR) enhancement necessary for higher spatial resolution imaging in magnetic resonance imaging (MRI) system. The proposed method combines compressed-sensing (CS) technique with key-hole acquisitions. It uses the average of an image acquired by CS and images obtained by key-hole-based acquisitions. This method is called CS averaging with key-hole acquisitions (CSAK). The feasibility of CSAK was evaluated with anthropomorphic phantom studies at 3.0T MRI. SNR and full-width at half-maximum (FWHM) measured from CSAK were compared to those of other methods, such as CS averaging with multiple acquisitions (CSAM), CS averaging with single acquisition (CSAS), conventional data acquisition, and images obtained using Gaussian-smoothing filters. While CSAS required the least scan time, it showed the poorest SNR. CSAM and CSAK showed higher SNR than the conventional data acquisition method with a full k-space. CSAM and CSAK also had spatial resolution performance comparable to that of full k-space-based image. CSAK required the least sampling points. Therefore, it required less scan time than those for CSAM and conventional single full k-space acquisition without averaging. In this study, we found that signal averaging for higher SNR with higher spatial resolution image without increasing the scan time could be achieved by CS-based averaging with key-hole acquisitions. Therefore, the proposed CSAK method could be used for high spatial resolution imaging required for higher SNR in MRI system.

Today, contrast agents are used to improve the sensitivity of magnetic resonance imaging (MRI) to detect pathologic structures. Ferrite nanoparticles are a class of superparamagnetic contrast agents in MRI. In this study, Zn_0.5Ni_0.5Fe₂O₄ nanoparticles were synthesized via precipitation method and coated with dextrin to increase the solubility and biocompatibility. The morphology, size, structure, and magnetic properties of nanoparticles were investigated. These nanoparticles have superparamagnetic property with a narrow size distribution with a mean diameter of about 20.5 ± 3.2 nm. MRI study using phantom agar shows that these nanoparticles can be used as an effective contrast agent for T₂ and \(T_{2}^{*}\)-weighted imaging. The relaxivities of r₂ and \(r_{2}^{*}\) are 8.78 and 82.08 s⁻¹ mmol L⁻¹, respectively. From these findings, it is possible that dextrin-coated Zn_0.5Ni_0.5Fe₂O₄ nanoparticles can be used as a good negative contrast agent in MRI.

We developed two digital magnetic resonance imaging (MRI) consoles using general-purpose digital instruments and microcontroller boards. The first console consisted of a digital oscilloscope (8-bit resolution, 250-MHz sampling frequency), an arbitrary waveform generator (14-bit resolution, 100-MHz sampling frequency), and three 32-bit microcontroller boards. The second console consisted of a digital oscilloscope (16-bit resolution, 1-GHz sampling frequency) with a built-in waveform generator (14-bit resolution, 200-MHz sampling frequency) and three 32-bit microcontroller boards. MRI experiments were performed using a 1.0-T and 90-mm gap yokeless permanent magnet to evaluate the MRI consoles. Three-dimensional spin-echo and gradient-echo images were successfully acquired using the first and second MRI consoles using an undersampling technique and RF phase correction. We concluded that the digital MRI consoles could be built using general-purpose digital instruments and microcontroller boards at a reduced cost and within a short development time.