CT截断区域对食管癌患者放疗计划剂量学影响

目的 探讨CT图像截断区域对胸中段食管癌容积调强计划(VMAT)中靶区和危及器官的剂量学影响。方法 选取15例胸中段食管癌患的CT图像,设置圆形掩膜使得截断区域体积占手臂体积的10%、20%、30%和40%,得到相应的截断CT,真实CT记为CT0。在CT0上制作2组放疗计划,一组为采用全弧的VMAT＿1F,一组为采用避开手臂的三弧VMAT＿3F,并将计划复制至4种截断CT。使用Wilcoxon符号秩检验比较不同计划的剂量学差异。结果 与CT0中VMAT＿1F相比,CT0中VMAT＿3F降低肺的D_mean和V₅,但增加了脊髓的D_max、心脏的D_mean和肺的V₂₀。VMAT＿3F中,4种截断CT中的剂量学参数与CT0中的没有统计学差异(均P> 0.05)。VMAT＿1F中,除均匀性指数HI和脊髓D_max外,4种截断CT中的剂量学参数与CT0中的均有统计学差异(P <0.05),且剂量学差异随着截断区域体积比的增加而增大。结论 临床中应采集完整的C...     

Direct microscopic monitoring of initial and dynamic clot lysis using plasmin or rt-PA in an in vitro flow system

Introduction

Plasmin is a direct-acting thrombolytic agent with a favorable safety profile upon intra-arterial delivery in pre-clinical and phase I studies. However, the thrombolytic efficacy of plasmin, relative to that of rt-PA, remains to be established. We have compared the dynamics of clot lysis with plasmin or rt-PA in an in vitro perfusion system, in which thrombolytic agent is administered locally, allowed to induce lysis for short intervals, then washed with plasma in a re-circulation circuit.

Materials and Methods

Whole blood human clots were prepared in observation chambers, exposed to plasmin or rt-PA at equimolar concentrations (1.2/1.0, 1.8/1.5 and 2.4/2.0 mg/ml) for measured intervals of time, followed by perfusion with human plasma. Clot size was monitored by digital analysis of sequential photographs obtained through an optical microscope.

Results

Plasma perfusion after incubation with thrombolytic agent rapidly removed superficial clot fragments. This initial decrease in clot size was greater with plasmin than with rt-PA when tested at the highest concentrations of agent (0.63 ± 0.11 vs. 0.30 ± 0.11, p = 0.001 for clots with non-cross-linked fibrin and 0.53 ± 0.15 vs. 0.14 ± 0.15, p = 0.02, for clots with cross-linked-fibrin). Subsequent clot lysis during plasma flow was greater after prior incubation with rt-PA. Longer incubation times of plasmin resulted in larger portions of the clot being washed free. Repeated plasmin incubations and plasma perfusions of a clot successfully induced stepwise reductions in clot size.

Conclusions

Initial clot lysis is greater with direct exposure using plasmin than rt-PA. During washout and circulation with plasma, rt-PA induced continued clot lysis, while plasmin lysis was curtailed, presumably because of plasmin inhibition.     

Dose reduction with iterative reconstruction: Optimization of CT protocols in clinical practice

ObjectivesTo create an adaptable and global approach for optimizing MDCT protocols by evaluating the influence of acquisition parameters and Iterative Reconstruction (IR) on dose reduction and image quality.Materials and methodsMDCT acquisitions were performed on quality image phantom by varying kVp, mAs, and pitch for the same collimation. The raw data were reconstructed by FBP and Sinogram Affirmed Iterative Reconstruction (SAFIRE) with different reconstruction kernel and thickness. A total of 4032 combinations of parameters were obtained. Indices of quality image (image noise, NCT, CNR, SNR, NPS and MTF) were analyzed. We developed a software in order to facilitate the optimization between dose reduction and image quality. Its outcomes were verified on an adult anthropomorphic phantom.ResultsDose reduction resulted in the increase of image noise and the decrease of SNR and CNR. The use of IR improved these indices for the same dose without affecting NCT and MTF. The image validation was performed by the anthropomorphic phantom. The software proposed combinations of parameters to reduce doses while keeping indices of the image quality adequate. We observed a CTDIvol reduction between −44% and −83% as compared to the French diagnostic reference levels (DRL) for different anatomical localization.ConclusionThe software developed in this study may help radiologists in selecting adequate combinations of parameters that allows to obtain an appropriate image with dose reduction.     

Reduced field-of-view MRI with two-dimensional spatially-selective RF excitation and UNFOLD.

When the region of interest (ROI) is smaller than the object, one can increase MRI speed by reducing the imaging field of view (FOV). However, when such an approach is used, features outside the reduced FOV will alias into the reduced-FOV image along the phase-encoding direction. Reduced-FOV methods are designed to correct this aliasing problem. In the present study, we propose a combination of two different approaches to reduce the acquired FOV: 1) two-dimensional (2D) spatially-selective RF excitation, and 2) the unaliasing by Fourier-encoding the overlaps using the temporal dimension (UNFOLD) technique. While 2D spatially-selective RF excitation can restrict the spins excited within a reduced FOV, the UNFOLD technique can help to eliminate any residual aliased signals and thus relaxes the requirement for a long RF excitation pulse. This hybrid method was implemented for MR-based temperature mapping, and resulted in artifact-free images with a fourfold improvement in temporal resolution.     

Time-resolved 3D contrast-enhanced MRA of an extended FOV using continuous table motion.

A method is presented for acquiring 3D time-resolved MR images of an extended (>100 cm) longitudinal field of view (FOV), as used for peripheral MR angiographic runoff studies. Previous techniques for long-FOV peripheral MRA have generally provided a single image (i.e., with no time resolution). The technique presented here generates a time series of 3D images of the FOV that lies within the homogeneous volume of the magnet. This is achieved by differential sampling of 3D k-space during continuous motion of the patient table. Each point in the object is interrogated in five consecutive 3D image sets generated at 2.5-s intervals. The method was tested experimentally in eight human subjects, and the leading edge of the bolus was observed in real time and maintained within the imaging FOV. The data revealed differential bolus velocities along the vasculature of the legs.     

Noninvasive thermometry using hyperfine-shifted MR signals from paramagnetic lanthanide complexes

MR thermometry techniques based on the strong water ¹H signal provide high spatial and temporal resolution and have shown promise for applications such as laser surgery and RF ablation. However, these techniques have low temperature sensitivity for hyperthermia applications and are greatly influenced by local motion and susceptibility variations. ¹H NMR signals from paramagnetic lanthanide complexes of Pr³⁺, Yb³⁺ and Tm³⁺ show up to 300-fold stronger temperature dependence compared to the water ¹H signal. In addition, ¹H chemical shifts of many of these complexes are insensitive to other factors such as the concentration of the paramagnetic complex, pH, [Ca²⁺], and the presence of plasma macro-molecules and ions. Applications of lanthanide complexes for temperature measurement in intact animals and the feasibility of mapping temperatures in phantoms have been demonstrated. Among all the lanthanide complexes examined so far, thulium 1,?4,?7,?10-tetramethyl-1,?4,?7,?10-tetraazacyclododecane-1,?4,?7,?10-tetraacetate (TmDOTMA^?) appears to be the most attractive for in vivo MR thermometry. The ¹H signal from the methyl groups on this complex is relatively intense because of 12 equivalent protons and provides high temperature sensitivity because of the large paramagnetic shifts induced by thulium. The possibility of imaging TmDOTMA²—in intact animals at physiologically safe concentrations has recently been demonstrated. Overall, MR thermometry methods based on hyperfine-shifted MR signals from paramagnetic lanthanide complexes appear promising for animal applications, but further studies relating to acceptable dose and signal-to-noise ratio are necessary before clinical use.