Preliminary Study Of Peripheral MRA With New Techniques And Self-designed USPIO

Objective The purpose of this study was to investgate the image quality and diagnostic performance achieved with low dose (0.15 mmol/kg) of Gd-DTPA and parallel acquisition technique in patients with PAOD undergoing peripheral CE MRA with high spatial resolution at open-bore 3.0T scanner.Materials and Methods1?22 patients with known PAOD were enrolled and underwent peripheral arteries CE MRA. According to the Fontaine classification for PAOD, stage II 13 patients; stage?six patients; and stage IV in three patients.2?All patients underwent CE MRA and DSA. And, in case three station could not cover the whole peripheral arteries, the forth station with the same parameter with the third was initiated.3D FLASH sequence was used with the following patameters: TR),2.89-3.16ms; TE,1.05-1.19ms; voxel size of pelvis, thigh and calf station:1.3×1.3×1.3,1.1×1.0×1.1 and 0.9×0.9×0.9mm3,respectively; FOV,362.5×400?362.5×400 and 350×400 mm2,respectively; accelerate factor,3-4. The dose of Gd-DTPA was 0.15mmol/kg. Following MRA examination, DSA was performed on single leg of all patients.3?Image quality?SNR and CNR of CE MRA was evaluated and calculated by one radiologist. Each FOV on CE MRA sequence was assessed for image quality on a four-point scale as follows:1, poor; 2, moderate, moderate venous overlay; 3, good signal enhancement,almost no venous overlay; and 4, excellent visualization.SNR and CNR were calculated by using the common equations:SNR=SIa/Sdn; CNR =(SIa-SIm)/Sdn. SIais the mean SI of the arteries at the central of each station, SIm is the SI of the adjacent muscle, and Sdn is the standard deviation of background noise (size of ROI was 40-60 pixels).Considering a stenosis greater than 50% or occlusion as positive, vessel disease on CE MRA was assess separately by two radiologists.and The images of DSA were retrospectively assessed by a radiologist.4?According type of data, A Wilcoxon rank sum test or variance test was used to evaluate the significance of the differences in image quality scores assigned. And LSD was used for pairwise comparison.P<05 was used as the criterion to indicate a statistically significant difference. The degree of interobserver agreement for detection of arterial stenosis were determined by calculating the Kappa coefficient. Spearman rank correlation coefficient was used for the relationship between contrast-enhanced MR angiography and DSA, in terms of categories of stenosis.Results1?All 22 patients successfully underwent MRA and DSA. Three of them underwent CE MRA with four stations.2?All undiagnostic segments of MRA were calf segments; There was no significant difference for the mean image quality score of different station (P=0.27, >0.05).There was significant difference for SNR and CNR of different station (P=0.04,0.02, P<0.05). There was no significant difference between SNR and CNR of pelvic and thigh station (P=0.95 and 0.78, respectively,>0.05), but SNR and CNR of calf segments was inferior compared with other image stations.3?A total of 498 segments were graded for stenosis. For vessel stenosis, Cohen's statistics revealed excellent agreement between the two observers (Kappa=0.96).4?A total of 181 arterial segments were compared with DSA. And, relevant stenoses were correctly identified by observer 1 in 161 (88.95%) segments and by observer 2 in 160 (88.40%) segments. There was a significant correlation between DSA and contrast-enhanced MR angiography for the degree of stenosis (reader 1: Rs=0.78, P=0.00<0.05; reader 2:Rs=0.76, P=0.00<0.05)Conclusion1?At this open-bore 3.0T scanner, high spatial resolution peripheral magnetic resonance angiographyhe was achieved with 0.15 mmol/kg dose of Gd-GDTA.2?Using parallel acquisition technique with higher accelerated factor, good image quality and high spatial resolution can be achieved to improve the diagnostic capability of CE MRA. As a result, agreement between the two observers was excellent, and there was a significant correlation between DSA and CE MRA for the degree of stenosis.3?Compared with pelvic and thigh station, SNR and CNR of calf station was inferior, and venous overlap hampered the image quality of some arterial segment of cal. So, combined with other new technique, the protocol in this study can be used as reference standard for the following study concerning unenhanced MRA technique.Part Two Infrapopliteal MR Angiography at 3.0T: Comparison of Fresh Blood Imaging with Variable Flip Angle and Contrast-enhanced MRA--a Intraindividual StudyObjective The purpose of this study was to evaluate diagnostic performance of this newly optimized ECG-gated Fresh blood imaging with variable flip angle technique on our 3.0T system as compared to 3D CE MRA and DSA for assessment of calf arteries in patients with PAOD.Materials and Methods 64 patients with suspected or known PAOD were enrolled and underwent unenhanced MRA (UE MRA), of calf arteries, time-resolved CE MRA (TCE) of calf arteries, and bolus-chase CE MRA (BCE) of lower peripheral arteries at 3.0 T. Image quality of UE MRA was evaluated and compared with contrast-enhanced MRA, Agreement between UE MRA and BCE/TCE in showing the degree of stenosis and visualized length was also assessed. X-ray angiography was performed on single leg of 10 patients before possible interventional treatment. using x-ray angiography as the reference standard, sensitivity, specificity, PPV and NPV were calculated for UE MRA and BCE/TCE, considering a stenosis greater than 50% or occlusion as positive. Furthermore, sensitivity and specificity between UE MRA and BCE/TCE were compared.Results1?Sixty-one out of 64 patients successfully underwent the whole MRA series. For UE MRA,852 of 960 segments (88.75%) were diagnostic; There was no significant difference for the mean image quality score on UE MRA and BCE (P=0.054>0.05). In UE MRA image quality of eight patients with arrhythmia, only 21 of 120 segments (17.5%) were nondiagnostic and the mean score of image quality in most patients on UE MRA reached 3-4.2?A total of 852 segments were graded for stenosis and length. For stenosis and visualized segmental length, Cohen's statistics revealed good agreement between UE MRA and BCE/TCE with a Kappa value of 0.77 and 0.75, respectively. When using BCE/TCE as reference standard, disease in 98 segments (11.50%) were overestimated?Visualized segmental length was underestimated in 59 segments (6.92%) by UE MRA.3?A total of 63 arterial segments were well opacified and diagnostic at X-ray angiography. And 55 of 63 (87.31%) segments were demonstrated correctly at UE MRA, with overall sensitivity and specificity of UE MRA in depicting severe stenosis and occlusion being 91.89% and 80.77%, respectively; PPV and NPV being 87.18% and 87.50%, respectively (Table 4). There was no significant difference between UE MRA and BCE/TCE concerning its sensitivity and specificity (P=0.63 and 1, respectively, P>0.05).Conclusion1?In this study, we demonstrated the high diagnostic capability of UE MRA with SPACE, parallel imaging and MT technique at 3.0T. Pure arteriograms with a small voxel siz can be achieved in the calf with no need of exogenous contrast materials.2?However, It should be kept in mind that there may be cases where the pulsatility of the target artery which this technique relies on may not be present or severely attenuated, in which case the visualization of the vessel of the interest may not be possible.3?In conclusion, It may play a useful role as a supplement to BCE MRA in the calf when venous contamination frequently occurs and screening high risk patients?Part ThreeThe Preliminary Study of Relaxivity in Distilled Water and MRA in Rabbits with Self-designed USPIOOneRelaxivity of Zwitterionic Nanoparticles and Poly Acrylic acid Coated Fe3O4 Nanoparticles in Comparison with Gd-DTPA and SH U 555 C at 1.5 and 3.0 TObjective In this study we evaluated the R1 and R2 of zwitterionic nanoparticles and poly acrylic acid coated Fe3O4 nanoparticles in comparison with Gd-DTPA and SHU 555 C at 1.5 and 3T.Materials and Methods1?The nanoparticles (PM) were synthesized by a microwave assisted polyol process, zwitterionic structure can be introduced onto the surface of PM. This zwitterionic nanoparticles (ZM) with mild positive charge has long blood half-life and still remain the small hydrodynamic size which is critical for MR blood pool contrast agents.2?Decreasing concentrations of contrast agents in pure water solution were evaluated with 1.5 and 3T clinical scanners. Pulse sequences comprised axial IR TSE sequences with fixed TR?TE and multiple TIs, and TSE sequences with fixed TR and increasing TEs. 3?Signal intensity measurements were used to calculate T1 and T2 relaxation times of all samples, assuming a monoexponential signal decay.Results1?At 1.5T, R1 of Gd-DTPA is lowest (3.12mM·s-1); R1 of ZM, PM and SHU 555 C were 9.29 mM·s-1,9.85 mM·s-1 and 10.31mM·s-1, respectively, the order of R2 from low to high was Gd-DTPA, ZM and PM, SHU 555 C, R2/R1 of SH U 555 C was highest, PM, ZM declined in turn, R2/R1 of Gd-DTPA was the lowest.2?At 3.0T, the order of R1 and R2 from high to low were PM, ZM, SHU 555 C and Gd-DTPA, R2/R1 of SH U 555 C was highest, ZM and PM declined in turn, R2/R1 of Gd-DTPA was the lowest.3?At the same field strength, R1 of all contrast agents decreased with increasing field strength, but Gd-DTPA decreased slightly. R2 decreased with increasing field strength except ZM, and SH U 555 C decreased most significantly. R2/R1 ratio of PM?ZM and SH U 555 C at 3.0T were higher than 1.5T, insteadly, R2/R1 of Gd-DTPA decreased with increasing field strength,Conclusion1?R1 of Gd-DTPA was lower, R2/R1 decreased with increasing field strength, so, Gd-DTPA was better at 3.0T, compared with 1.5T.2?compared with 1.5T, R1 of SHU 555 C decreased and R2/R1 increased with increasing field strength, the tendency PM and ZM at different were similar with SHU 555 C.3?This ZM with mild positive charge has long blood half-life. And, it has the potential value in animal imaging studies.TwoEffect of Field Strengths on MRA Comparison of an USPIO Blood-Pool Contrast Agent, Gd-DTPA and SHU 555 C in Rabbits at 1.5 and 3.0 TObjectives We sought to compare the intravascular enhancement of three USPIO blood-pool contrast agents to SHU 555 C and Gd-DTPA for first-pass and equilibrium phase CE MRA at 1.5 and 3.0 T in rabbits.Materials and Methods1?Eighteen of Male New Zealand rabbit were randomizedly divided into three groups. CE MRA at 1.5 and 3.0 T was performed before and after contrast agent administration at several time points (0s,19s,38s,5,10,15,20,25,30, 35,40,45,50,60,90,120 min) after the manual intravenous injection of 40?mol Fe/kg body weight of ZM and SH U 555 C (Schering AG, Berlin, Germany) and 0.2mmol/kg body weight Gd-DTPA (Magnevist; Schering AG, Berlin, Germany). MRA was performed with comparable acquisition parameters at both field strengths.SNR and CNR were calculated by using the common equations:SNR SIa/Sdn; CNR=(SIa-SIm)/Sdn. SIais the mean SI of the abdominal aorta, SIm is the SI of the right psoas muscle, and Sdn is the standard deviation of background noiseFor different field strength, SNR and CNR were compared with paired t or t' test; for each time point, SNR and CNR of statistical evaluation was performed by using the analysis of variance test and LSD was used for pairwise comparison.Results1?At 1.5T, there was no significant different among SNR and CNR of Gd-DTPA, SHU 555 C and ZM at first-pass phase(P=0.258?0.314,>0.05). At each time points from 10min to 2 hour, there was different among three groups. From 15 minutes to 2 hour, SNR and CNR of ZM were higher than the rest two groups.2?At 3.0T, there was significant different among SNR and CNR of Gd-DTPA, SHU 555 C and ZM at each time points(P<0.05).At first to third time point, SNR and CNR of Gd-DTPA were highest, ZM was better than or equal to SHU 555 C. From 5 minutes to 2 hour, SNR and CNR of ZM were higher than the rest two groups (P<0.05).3?SNR and CNR of Gd-DTPA increased with increasing field strength (P=0.02,0.002, respectively<0.05), and SNR and CNR of ZM also increased (P=0.00,0.00<0.05), SNR and CNR of SH U 555 C, measured after intravenous injection, did not change significantly with increasing field strength (P=0.61,0.82,>0.05). Conclusion1?With the dose of 40?mol/kg, at 1.5 T, at the first-by phase, SNR and CNR of ZM was similar with Gd-DTPA, SHU 555 C. At 3.0 T, SNR and CNR of ZM was lower than Gd-DTPA,but better than SHU 555 C.2?At both field strength and each equilibrial time point, CNR and SNR of ZM were significantly higher compared with the others.3?The SNR and CNR ofZM significantly increased at 3.0 T, measured after intravenous injection. But No SNR or CNR gain was observed for SHU 555 C.At 3.0T, ZM was superior, compared with SHU 555 C.