Treating Brain Tumor with Microbeam Radiation Generated by a Compact Carbon-Nanotube-Based Irradiator: Initial Radiation Efficacy Study.

Microbeam radiation treatment (MRT) using synchrotron radiation has shown great promise in the treatment of brain tumors, with a demonstrated ability to eradicate the tumor while sparing normal tissue in small animal models. With the goal of expediting the advancement of MRT research beyond the limited number of synchrotron facilities in the world, we recently developed a compact laboratory-scale microbeam irradiator using carbon nanotube (CNT) field emission-based X-ray source array technology. The focus of this study is to evaluate the effects of the microbeam radiation generated by this compact irradiator in terms of tumor control and normal tissue damage in a mouse brain tumor model. Mice with U87MG human glioblastoma were treated with sham irradiation, low-dose MRT, high-dose MRT or 10 Gy broad-beam radiation treatment (BRT). The microbeams were 280 µm wide and spaced at 900 µm center-to-center with peak dose at either 48 Gy (low-dose MRT) or 72 Gy (high-dose MRT). Survival studies showed that the mice treated with both MRT protocols had a significantly extended life span compared to the untreated control group (31.4 and 48.5% of life extension for low- and high-dose MRT, respectively) and had similar survival to the BRT group. Immunostaining on MRT mice demonstrated much higher DNA damage and apoptosis level in tumor tissue compared to the normal brain tissue. Apoptosis in normal tissue was significantly lower in the low-dose MRT group compared to that in the BRT group at 48 h postirradiation. Interestingly, there was a significantly higher level of cell proliferation in the MRT-treated normal tissue compared to that in the BRT-treated mice, indicating rapid normal tissue repairing process after MRT. Microbeam radiation exposure on normal brain tissue causes little apoptosis and no macrophage infiltration at 30 days after exposure. This study is the first biological assessment on MRT effects using the compact CNT-based irradiator. It provides an alternative technology that can enable widespread MRT research on mechanistic studies using a preclinical model, as well as further translational research towards clinical applications.

Delayed contrast enhancement imaging of a murine model for ischemia reperfusion with carbon nanotube micro-CT.

We aim to demonstrate the application of free-breathing prospectively gated carbon nanotube (CNT) micro-CT by evaluating a myocardial infarction model with a delayed contrast enhancement technique. Evaluation of murine cardiac models using micro-CT imaging has historically been limited by extreme imaging requirements. Newly-developed CNT-based x-ray sources offer precise temporal resolution, allowing elimination of physiological motion through prospective gating. Using free-breathing, cardiac-gated CNT micro-CT, a myocardial infarction model can be studied non-invasively and with high resolution. Myocardial infarction was induced in eight male C57BL/6 mice aged 8-12 weeks. The ischemia reperfusion model was achieved by surgically occluding the LAD artery for 30 minutes followed by 24 hours of reperfusion. Tail vein catheters were placed for contrast administration. Iohexol 300 mgI/mL was administered followed by images obtained in diastole. Iodinated lipid blood pool contrast agent was then administered, followed with images at systole and diastole. Respiratory and cardiac signals were monitored externally and used to gate the scans of free-breathing subjects. Seven control animals were scanned using the same imaging protocol. After imaging, the heart was harvested, cut into 1mm slices and stained with TTC. Post-processing analysis was performed using ITK-Snap and MATLAB. All animals demonstrated obvious delayed contrast enhancement in the left ventricular wall following the Iohexol injection. The blood pool contrast agent revealed significant changes in cardiac function quantified by 3-D volume ejection fractions. All subjects demonstrated areas of myocardial infarct in the LAD distribution on both TTC staining and micro-CT imaging. The CNT micro-CT system aids straightforward, free-breathing, prospectively-gated 3-D murine cardiac imaging. Delayed contrast enhancement allows identification of infarcted myocardium after a myocardial ischemic event. We demonstrate the ability to consistently identify areas of myocardial infarct in mice and provide functional cardiac information using a delayed contrast enhancement technique.

Image-guided microbeam irradiation to brain tumour bearing mice using a carbon nanotube x-ray source array.

Microbeam radiation therapy (MRT) is a promising experimental and preclinical radiotherapy method for cancer treatment. Synchrotron based MRT experiments have shown that spatially fractionated microbeam radiation has the unique capability of preferentially eradicating tumour cells while sparing normal tissue in brain tumour bearing animal models. We recently demonstrated the feasibility of generating orthovoltage microbeam radiation with an adjustable microbeam width using a carbon nanotube based x-ray source array. Here we report the preliminary results from our efforts in developing an image guidance procedure for the targeted delivery of the narrow microbeams to the small tumour region in the mouse brain. Magnetic resonance imaging was used for tumour identification, and on-board x-ray radiography was used for imaging of landmarks without contrast agents. The two images were aligned using 2D rigid body image registration to determine the relative position of the tumour with respect to a landmark. The targeting accuracy and consistency were evaluated by first irradiating a group of mice inoculated with U87 human glioma brain tumours using the present protocol and then determining the locations of the microbeam radiation tracks using γ-H2AX immunofluorescence staining. The histology results showed that among 14 mice irradiated, 11 received the prescribed number of microbeams on the targeted tumour, with an average localization accuracy of 454 µm measured directly from the histology (537 µm if measured from the registered histological images). Two mice received one of the three prescribed microbeams on the tumour site. One mouse was excluded from the analysis due to tissue staining errors.

Detection of aortic arch calcification in apolipoprotein E-null mice using carbon nanotube-based micro-CT system.

BACKGROUND: We performed in vivo micro-computed tomography (micro-CT) imaging using a novel carbon nanotube (CNT)-based x-ray source to detect calcification in the aortic arch of apolipoprotein E (apoE)-null mice. METHODS AND RESULTS: We measured calcification volume of aortic arch plaques using CNT-based micro-CT in 16- to 18-month-old males on 129S6/SvEvTac and C57BL/6J genetic backgrounds (129-apoE KO and B6-apoE KO). Cardiac and respiratory gated images were acquired in each mouse under anesthesia. Images obtained using a CNT micro-CT had less motion blur and better spatial resolution for aortic calcification than those using conventional micro-CT, evaluated by edge sharpness (slope of the normalized attenuation units, 1.6±0.3 versus 0.8±0.2) and contrast-to-noise ratio of the calcifications (118±34 versus 10±2); both P<0.05, n=6. Calcification volume in the arch inner curvature was 4 times bigger in the 129-apoE KO than in the B6-apoE KO mice (0.90±0.18 versus 0.22±0.10 mm(3), P<0.01, n=7 and 5, respectively), whereas plaque areas in the inner curvature measured in dissected aorta were only twice as great in the 129-apoE KO than in the B6-apoE KO mice (6.1±0.6 versus 3.7±0.4 mm(2), P<0.05). Consistent with this, histological calcification area in the plaques was significantly higher in the 129-apoE KO than in the B6-apoE KO mice (16.9±2.0 versus 9.6±0.8%, P<0.05, 3 animals for each). CONCLUSIONS: A novel CNT-based micro-CT is a useful tool to evaluate vascular calcifications in living mice. Quantification from acquired images suggests higher susceptibility to calcification of the aortic arch plaques in 129-apoE KO than in B6-apoE KO mice.

Zr- and Hf-based nanoscale metal-organic frameworks as contrast agents for computed tomography.

Nanoscale metal-organic frameworks (NMOFs) of the UiO-66 structure containing high Zr (37 wt%) and Hf (57 wt%) content were synthesized and characterized, and their potential as contrast agents for X-ray computed tomography (CT) imaging was evaluated. Hf-NMOFs of different sizes were coated with silica and poly(ethylene glycol) (PEG) to enhance biocompatibility, and were used for in vivo CT imaging of mice, showing increased attenuation in the liver and spleen.

Non-contact respiration monitoring for in-vivo murine micro computed tomography: characterization and imaging applications.

A cone beam micro-CT has previously been utilized along with a pressure-tracking respiration sensor to acquire prospectively gated images of both wild-type mice and various adult murine disease models. While the pressure applied to the abdomen of the subject by this sensor is small and is generally without physiological effect, certain disease models of interest, as well as very young animals, are prone to atelectasis with added pressure, or they generate too weak a respiration signal with this method to achieve optimal prospective gating. In this work we present a new fibre-optic displacement sensor which monitors respiratory motion of a subject without requiring physical contact. The sensor outputs an analogue signal which can be used for prospective respiration gating in micro-CT imaging. The device was characterized and compared against a pneumatic air chamber pressure sensor for the imaging of adult wild-type mice. The resulting images were found to be of similar quality with respect to physiological motion blur; the quality of the respiration signal trace obtained using the non-contact sensor was comparable to that of the pressure sensor and was superior for gating purposes due to its better signal-to-noise ratio. The non-contact sensor was then used to acquire in-vivo micro-CT images of a murine model for congenital diaphragmatic hernia and of 11-day-old mouse pups. In both cases, quality CT images were successfully acquired using this new respiration sensor. Despite the presence of beam hardening artefacts arising from the presence of a fibre-optic cable in the imaging field, we believe this new technique for respiration monitoring and gating presents an opportunity for in-vivo imaging of disease models which were previously considered too delicate for established animal handling methods.

Prospective respiratory gated carbon nanotube micro computed tomography.

RATIONALE AND OBJECTIVES: Challenges remain in the imaging of the lungs of free-breathing mice. Although computed tomographic (CT) imaging is near optimal from a contrast perspective, the rapid respiration rate, limited temporal resolution, and inflexible x-ray pulse control of most micro-CT scanners limit their utility in pulmonary imaging. Carbon nanotubes (CNTs) have permitted the development of field emission cathodes, with rapid switching and precise pulse control. The goal of this study was to explore the utility of a CNT-based micro-CT system for application in quantitative pulmonary imaging. MATERIALS AND METHODS: Twelve CB57/B6 mice were imaged during peak inspiration and end-exhalation using the CNT micro-CT system. The respiratory trace was derived from a sensor placed underneath the abdomen of the animal. Animals were allowed to breathe freely during the imaging under isoflurane anesthesia. Images were reconstructed using isotropic voxels of 77-µm resolution (50 kVp, 400 projections, 30-ms x-ray pulse). Lung volumes were measured with region-growing techniques and thresholds derived from the surrounding air and soft tissues. Basic functional parameters, including tidal volume, functional reserve capacity and minute volume, were also calculated. RESULTS: The average scan time was 13.4 ± 1.8 minutes for each phase of the respiratory cycle. Mean lung volumes at peak inspiration and end-expiration were 0.23 ± 0.026 and 0.11 ± 0.024 mL, respectively. The average minute volume was 11.93 ± 2.64 mL/min. CONCLUSIONS: The results of this study demonstrate the utility of a CNT-based micro-CT system in acquiring prospectively gated images from free-breathing mice for obtaining physiologic data. This technique provides an alternative to breath-hold techniques requiring intubation and offers greater dose efficiency than retrospective gating techniques.

Prospective-gated cardiac micro-CT imaging of free-breathing mice using carbon nanotube field emission x-ray.

PURPOSE: Carbon nanotube (CNT) based field emission x-ray source technology has recently been investigated for diagnostic imaging applications because of its attractive characteristics including electronic programmability, fast switching, distributed source, and multiplexing. The purpose of this article is to demonstrate the potential of this technology for high-resolution prospective-gated cardiac micro-CT imaging. METHODS: A dynamic cone-beam micro-CT scanner was constructed using a rotating gantry, a stationary mouse bed, a flat-panel detector, and a sealed CNT based microfocus x-ray source. The compact single-beam CNT x-ray source was operated at 50 KVp and 2 mA anode current with 100 microm x 100 microm effective focal spot size. Using an intravenously administered iodinated blood-pool contrast agent, prospective cardiac and respiratory-gated micro-CT images of beating mouse hearts were obtained from ten anesthetized free-breathing mice in their natural position. Four-dimensional cardiac images were also obtained by gating the image acquisition to different phases in the cardiac cycle. RESULTS: High-resolution CT images of beating mouse hearts were obtained at 15 ms temporal resolution and 6.2 lp/mm spatial resolution at 10% of system MTF. The images were reconstructed at 76 microm isotropic voxel size. The data acquisition time for two cardiac phases was 44 +/- 9 min. The CT values observed within the ventricles and the ventricle wall were 455 +/- 49 and 120 +/- 48 HU, respectively. The entrance dose for the acquisition of a single phase of the cardiac cycle was 0.10 Gy. CONCLUSIONS: A high-resolution dynamic micro-CT scanner was developed from a compact CNT microfocus x-ray source and its feasibility for prospective-gated cardiac micro-CT imaging of free-breathing mice under their natural position was demonstrated.