MR imaging of biodegradable polymeric microparticles: a potential method of monitoring local drug delivery.

Gadolinium diethylenetriamine pentaacetic acid (Gd-DTPA) was encapsulated into biodegradable, bioadhesive polymeric microparticles to enable noninvasive monitoring of their local intravesical delivery with MRI. The microparticles were characterized by contrast agent encapsulation and release kinetics, T(1) relaxation rates, and contrast enhancement in vivo. The level of Gd-DTPA loading into microparticles was 14.3 +/- 0.6 mug/mg polymer. The measured T(1) relaxation rates of the microparticles showed a direct dependence on Gd-DPTA content. Both 1.5T and 4.7T MR scanners were used to image murine bladders instilled intravesically with Gd-DTPA-loaded particles in vivo. MR images showed ring-shaped regions of enhancement inscribing the bladder wall, which were attributed to the microparticles that were preferentially adherent to the mucosa lining the urothelium. The images of controls exhibited no such enhancement. The normalized signal intensities measured from post-instillation images were significantly greater (P < 0.05) than those in the pre-instillation images. Contrast enhancement was observed for at least 5 days after the initial instillation, although the enhancement decreased due to microparticle degradation or mucosa renewal. The localized distribution of biodegradable, bioadhesive microparticles encapsulating Gd-DTPA was successfully visualized with MRI in vivo, allowing particle-mediated delivery to be temporally and spatially monitored noninvasively.     

Radio-frequency-induced coagulation necrosis in rabbits: immediate detection at US with a synthetic microsphere contrast agent.

PURPOSE: To determine whether a synthetic ultrasonographic (US) contrast agent can be used to differentiate coagulation necrosis from untreated tumor immediately after radio-frequency ablative therapy. MATERIALS AND METHODS: VX2 (adenocarcinoma) tumors (0.8-1.5-cm diameter) were implanted into 12 rabbits. Gray-scale and color Doppler US were performed with or without intravenous injection of a US contrast agent composed of poly-lactide-co-glycolic acid polymeric (PLGA) microspheres (2-micron diameter) filled with perfluorocarbon gas. Radio frequency was applied to each nodule for 6 minutes at 127 mA +/- 33 (mean +/- SD) (tip temperature, 92 degrees C +/- 2). Repeat US with a second dose of the contrast agent was performed immediately after ablation. In four animals, a third dose was administered 30-120 minutes after ablation. Radiologic-histopathologic correlation was performed and included in vivo staining and studies of mitochondrial function. RESULTS: Intense contrast agent enhancement was seen throughout the tumor prior to ablation. At gray-scale US, ablation produced hyperechoic foci, which were within 1 mm of the foci identified at histopathologic examination in seven of 12 animals (58%). After the administration of contrast material, foci devoid of previously visualized enhancement, which measured 7.3-15.0 mm, were identified. These were within 1 mm of the size of the foci identified at histopathologic examination in 11 of 12 animals (92%, P < .01). In two animals, enhancement depicted viable tumor, which appeared hyperechoic, on nonenhanced images. On delayed images, hyperechoic areas decreased in size, whereas the nonenhanced region remained unchanged. CONCLUSION: A PLGA microspherical US contrast agent enabled the immediate detection of coagulation necrosis as a region devoid of contrast enhancement after radio-frequency ablation in rabbit hepatic tumors. Therefore, this agent could provide real-time guidance during complex ablative procedures and may provide an efficient technique for postprocedural assessment.     

Ideal Size Range for Embolic Agents in Interventional Oncology Experiments Involving Rat Models of Hepatocellular Carcinoma

PurposeTo optimize future translational research, this study aimed to determine the ideal range of sizes for embolic agents in interventional oncology experiments utilizing rat models of hepatocellular carcinoma (HCC).Materials and MethodsFifty-five male Sprague-Dawley rats were divided into 2 groups to evaluate the distribution of microparticles and tumor response rates. After implanting hepatoma cells into the rodent liver, fluorescent microparticles of sizes ranging from 5 to 35 μm were administered via the hepatic artery. In the first group, the distribution of microparticles was evaluated in hepatoma-free rats, and the tumor necrosis rates following administration of a predetermined aliquot of microparticles (0.4 mL) were measured in tumor-bearing rats. Thereafter, the 3 microparticle sizes associated with the best tumor response rates were chosen for analysis of the tumor necrosis rates following hepatic artery embolization until angiographic stasis is achieved in the second group.ResultsThe tendency for microparticles to distribute in nontarget organs increased as the microparticle size decreased below 15 μm. Tumor necrosis rates tended to be higher in rats treated with 15–19-μm microparticles than in those treated with 19–24-μm or 19–24-μm microparticles. The in-group deviation of the tumor necrosis rates was highest for microparticle sizes of 19–24 and 25–35 μm, which implies the proximal embolization of the hepatic artery for larger microparticle sizes. However, there was no statistical significance among the 3 groups (P = .095).ConclusionsThe 15–19-μm embolic agents were the most favorable for causing tumor necrosis without nontarget toxicity in the transarterial treatments of rat HCC models.     

PLGA微米与纳米载药颗粒用于药物携带与递送的比较研究

 

目的 通过评价聚乳酸-羟基乙酸共聚物(polylactic acid-glycolic acid copolymer,PLGA)微米颗粒(micron particle,MP)与纳米颗粒(nanoparticle,NP)的表面特征、载药能力、药物缓释能力及细胞吞噬能力等方面来比较阐述PLGA纳米与微米颗粒在细胞预处理与修饰中的合理应用。方法 分别制备PLGA纳米颗粒与微米颗粒,并进行表征;随后,比较其载药能力,并对药物的释放特征进行测定;最后,在不同时间点通过荧光强度评价两种颗粒与细胞结合或进入细胞的能力。结果 所制备的纳米粒与微米颗粒粒径分别分布在200~300 nm和2~4 μm;两种颗粒载药量相当,分别为14.3%和14.1%;在药物缓释方面,纳米颗粒存在显著的早期突释现象;微米颗粒释放缓慢,持续缓释可达一周左右;粒径相对小的纳米粒更容易进入或与细胞结合,共孵育12 h即达到最大值,微米颗粒相对较慢,最大值出现在共孵育24 h后。结论 PLGA纳米颗粒作为药物载体更适合于急性组织或细胞保护,微米颗粒更适合于慢性持续性保护。

     

Radiosensitization of ultrasmall GNP–PEG–cRGDfK in ALTS1C1 exposed to therapeutic protons and kilovoltage and megavoltage photons

Purpose: One of the promising radiosensitizers is the ultrasmall gold nanoparticle (GNP) with a hydrodynamic diameter?<3?nm. We studied functionalized ultrasmall GNPs (1.8?nm diameter) coated by polyethylene glycol (PEG) and conjugated with cyclic RGDfK (2.6?nm hydrodynamic diameter) for targeting of alpha(v) beta(3) integrin (α_vβ₃) in the murine ALTS1C1 glioma cell line.

Materials and methods: We investigated the uptake, toxicity and radiosensitivity of GNP–PEG–cRGDfKs in ALTS1C1 cells exposed to protons, kilovoltage photons and megavoltage photons. The in vitro uptake and toxicity of GNPs in the hepatocytes and Kupffer cells were assessed for murine AML12 hepatocyte and RAW 264.7 macrophage cell lines. The in vivo biodistribution of GNPs in the ALTS1C1 tumor model was tested using the inductively coupled plasma mass spectrometry.

Results: Results indicated GNPs accumulated in the cytoplasm with negligible toxicity for a moderate concentration of GNPs. Observed sensitizer enhancement ratios and dose enhancement factors are 1.21–1.66 and 1.14–1.33, respectively, for all radiations.

Conclusion: Ultrasmall GNP–PEG–cRGD can be considered as a radiosensitizer. For radiotherapy applications, the delivery method should be developed to increase the GNP uptake in the tumor and decrease the uptakes in undesirable organs.     

Magnetic poly(lactide‐co‐glycolide) and cellulose particles for MRI‐based cell tracking

Biodegradable, superparamagnetic microparticles and nanoparticles of poly(lactide‐co‐glycolide) (PLGA) and cellulose were designed, fabricated, and characterized for magnetic cell labeling. Monodisperse nanocrystals of magnetite were incorporated into microparticles and nanoparticles of PLGA and cellulose with high efficiency using an oil‐in‐water single emulsion technique. Superparamagnetic cores had high magnetization (72.1 emu/g). The resulting polymeric particles had smooth surface morphology and high magnetite content (43.3 wt % for PLGA and 69.6 wt % for cellulose). While PLGA and cellulose nanoparticles displayed highest r values per millimole of iron (399 sec^?1 mM^?1 for cellulose and 505 sec^?1 mM^?1 for PLGA), micron‐sized PLGA particles had a much higher r per particle than either. After incubation for a month in citrate buffer (pH 5.5), magnetic PLGA particles lost close to 50% of their initial r molar relaxivity, while magnetic cellulose particles remained intact, preserving over 85% of their initial r molar relaxivity. Lastly, mesenchymal stem cells and human breast adenocarcinoma cells were magnetically labeled using these particles with no detectable cytotoxicity. These particles are ideally suited for noninvasive cell tracking in vivo via MRI and due to their vastly different degradation properties, offer unique potential for dedicated use for either short (PLGA‐based particles) or long‐term (cellulose‐based particles) experiments. Magn Reson Med, 2011. © 2011 Wiley‐Liss, Inc.     

Sensitive particle acoustic quantification (SPAQ): a new ultrasound-based approach for the quantification of ultrasound contrast media in high concentrations

RATIONALE AND OBJECTIVES: Ultrasound contrast media (USCM) consisting of gas-filled microparticles (MPs) can be detected in tissue in extremely small amounts using the stimulated acoustic emission effect (SAE), which occurs after the destruction of MPs in an acoustic field. Limited by the spatial resolution of ultrasound devices, the displayed size of individual MPs/SAEs is in the range of millimeters rather than micrometers. Thus, more than approximately 1000 microparticles per milliliter led to complete SAE saturation in the image and cannot be quantified. We have developed a method to quantify microparticles in high concentrations by increasing the resolution. METHODS: We quantified gas-filled microparticles in an agar phantom containing 30,000 microparticles per mL with a defined overlap of consecutive images, thereby destroying the microparticles with high mechanical index and measuring the corresponding SAE effects using videodensitometry. RESULTS: In each image, only those particles that had not been previously destroyed were detected. The thickness of the slices containing SAE signals was thus determined by frame-to-frame displacement. Based on the reduced slice thickness and the resulting improved spatial resolution, individual microparticles were detected even in high microparticle concentrations. CONCLUSION: Sensitive particle acoustic quantification (SPAQ) allows the quantification of microparticles, even in high concentrations, based on a massive increase in resolution.     

In vitro release of vascular endothelial growth factor from gadolinium-doped biodegradable microspheres.

A drug delivery vehicle was constructed that could be visualized noninvasively with MRI. The biodegradable polymer poly(DL-lactic-co-glycolic acid) (PLGA) was used to fabricate microspheres containing vascular endothelial growth factor (VEGF) and the MRI contrast agent gadolinium diethylenetriamine pentaacetic acid (Gd-DTPA). The microspheres were characterized in terms of size, drug and contrast agent encapsulation, and degradation rate. The PLGA microspheres had a mean diameter of 48 +/- 18 microm. The gadolinium loading was 17 +/- 3 microg/mg polymer and the VEGF loading was 163 +/- 22 ng/mg polymer. Electron microscopy revealed that the Gd was dispersed throughout the microspheres and it was confirmed that the Gd loading was sufficient to visualize the microspheres under MRI. VEGF and Gd-DTPA were released from the microspheres in vitro over a period of approximately 6 weeks in three phases: a burst, followed by a slow steady-state, then a rapid steady-state. Biodegradable Gd-doped microspheres can be effectively used to deliver drugs in a sustained manner, while being monitored noninvasively with MRI.     

口服降钙素微粒制备工艺的研究

目的:制备口服降钙素微粒给药系统.方法:选用氨基酸环合脱水、环二聚化的方法合成二酮哌嗪,以二酮哌嗪作为包裹材料采用固化凝聚法制备降钙素微粒,通过正交设计筛选降钙素微粒的制备工艺,并对其物理形态、体外释放进行了研究.结果:微粒的物理性质稳定,在水溶液中的分散性好,平均粒径1～3μm,药物回收率74%,微球主药含量1.36%,体外释放符合零级方程.结论:此微粒系统在低pH条件下稳定,在生理环境中可溶解,可作为在胃液中不稳定药物特别是蛋白质和多肽类药物口服给药载体.     

携紫杉醇和Herceptin高分子造影剂联合超声体外寻靶及显影效果研究

目的 探讨携紫杉醇(Pac)和注射用曲妥珠单克隆抗体(Herceptin)高分子造影剂(Pac-PLGA-HER)联合超声体外寻靶能力及显影效果.方法 通过双乳化法和碳二亚胺法制备载Pac靶向高分子造影剂.将MCF-7细胞种植于12个培养皿中,培养24 h,分为4组,每组3个:非靶向造影剂组(Pac-PLGA组)、靶向造影剂组(Pac-PLGA-HER组)、靶向造影剂+超声组(Pac-PLGA-HER+超声组)和抗体封闭组.在激光共聚焦显微镜下对比观察高分子造影剂与细胞的结合能力.观察体外显影效果,并用DFY型定量仪进行定量,采用独立样本t检验进行统计学分析.结果 靶向载Pac高分子造影剂平均粒径为(596±12) nm,体外寻靶能力实验显示靶向载Pac高分子造影剂可与MCF-7细胞大量结合.体外显影实验示靶向与非靶向载Pac高分子造影剂平均声强分别为(134.50±10.19)和(135.11±11.49) dB,平均灰阶分别为147.83±11.12和148.50±12.63,两者比较差异均无统计学意义(t均为-0.097,P均＞0.05).结论 携Pac和Herceptin的高分子造影剂对高表达HER2的人乳腺癌MCF-7有较强的结合能力,在体外显影实验中有较好的显影效果.     

Changes produced by external radiation in parameters influencing intestinal permeability and microparticle uptake in vitro

PURPOSE: To determine the interaction between X-irradiation and in vitro intestinal microparticle uptake through Caco-2 epithelial cells. METHODS: Caco-2 cells were cultured on 3 microm porous membranes for 21 days, X-irradiated with 2 Gy or sham-irradiated, then incubated for 5 or 30 min and exposed apically for 30 min to 2 microm latex microparticles. Measurements included cell dimensions, from confocal microscope 'optical slices'; transepithelial resistance (TER) for tight junction (TJ) permeability; particle aggregation; and particle numbers on (adsorbed), in (intraepithelial) and through (submembranous) the epithelium. RESULTS: Irradiation alone reduced TJ permeability more than sham-treatment, more so 5 min than 30 min after treatment. Irradiated epithelia were more permeable to particles than the equivalent sham-irradiated or previously untreated (particle only) groups: the latter two were similar. Irradiation altered adsorbed particle numbers and increased submembranous counts: particle uptake correlated best with cell height. CONCLUSIONS: 2 Gy X-irradiation increased particle uptake and translocation through the epithelium. This correlated well with the TJ opening seen after particle exposure in irradiated samples and changes in cell morphology. New data on cell dimensions underlined the similarity in particle uptake between this in vitro epithelium and that in an in vivo model, highlighting the translational significance of the work.     

Nitrogen-filled liposomes as a vascular US contrast agent: preliminary evaluation.

Liposomes with a mean diameter of 1-2 microns were made to entrap nitrogen gas and tested as an ultrasound (US) contrast agent. The gas-filled liposomes, or Aerosomes (ImaRx Pharmaceutical, Tucson) were tested in vitro for size, stability, reflectivity, and acoustic characterization, and were tested in vivo for acute toxicity in mice and for cardiac imaging in rabbits after intravenous injection. Aerosomes have much greater reflectivity and higher attenuation than do standard liposomes and retain their acoustic properties after storage in aqueous media for several months. The interpolated median lethal dose of Aerosomes is approximately 2.5 mmol of lipid per kilogram, and the imaging dose is under 5 mumol of lipid per kilogram, yielding a potential therapeutic index of over 500 to 1. Postcontrast US images showed sustained enhancement of all four cardiac chambers as well as enhancement in the aorta, vena cava, and hepatic veins. Aerosomes hold promise as a contrast agent for cardiac and blood-pool imaging. Further work is in progress to characterize and develop this novel US contrast agent.     

Early experience in the use of Levovist ultrasound contrast in the evaluation of liver masses

The aim of the present paper was to assess the utility of Levovist in defining the pathology of liver masses. Levovist is a new ultrasound contrast agent consisting of galactose microparticles, air bubbles and palmitic acid. Prospective studies were performed in patients referred for further evaluation of known liver masses. Levovist was peripherally injected and colour Doppler ultrasound studies were performed. Findings were correlated with clinicopathology and three other imaging modalities: biphasic spiral CT, CT arterial portography and contrast MRI. Twenty-five patients were studied (15 male and 10 female) in the age range 25-74 years. Liver masses ranged from 0.5 to 7 cm in maximum diameter. Thirteen lesions were benign and 12 were malignant (four hepatomas (HCC) and eight metastases). Levovist enhancement occurred in 18 lesions. Of these, six were benign (four focal nodular hyperplasias (FNH) and two haemangiomas). All 12 malignant lesions demonstrated enhancement. The HCC showed a mosaic pattern of central and peripheral enhancement, and the FNH demonstrated a spoke-wheel pattern. It was not possible to distinguish between haemangiomas and malignant lesions. Non-enhancing lesions may well be benign, with all malignancies showing some enhancement. Characteristic enhancement patterns were found for HCC (mosaic) and FNH (spoke-wheel). It was not possible to distinguish between metastases and benign lesions (haemangiomas) when the pattern of enhancement was peripheral.     

Computed tomography of corpus luteal cysts

OBJECTIVE: To describe the computed tomography (CT) features of corpus luteal cysts. METHODS: We retrospectively identified 10 patients with a diagnosis of corpus luteal cysts established by ultrasound who had also undergone contemporaneous CT. A single attending radiologist, without knowledge of other clinical or radiologic findings, recorded the morphologic features of the cysts based on the CT images. RESULTS: The corpus luteal cyst seen at sonography was visible at CT in all 10 patients. All cysts were unilocular, with a mean density of 25 HU (range, 12 to 45). The mean maximum axial cyst diameter was 2.2 cm (range, 1.4 to 2.9). The mean cyst wall thickness was 3 mm (range, 2 to 4). All cyst walls were crenulated. Cyst wall enhancement was hyperdense in 6 cases, isodense in 3 cases, and hypodense in 1 case. Free fluid was seen in 9 of 10 patients. CONCLUSIONS: At CT, corpus luteal cysts are typically less than 3 cm in diameter and are characterized by a thick, crenulated, or hyperdense wall. Recognition of these CT findings should prevent misinterpretation or inappropriate management.     

Pharmacokinetic and safety study of doxorubicin-eluting beads in a porcine model of hepatic arterial embolization

PURPOSE: To present the pathologic and pharmacokinetic findings from hepatic embolization in a porcine model comparing doxorubicin-eluting beads with bland embolization and to correlate these findings with in vitro release kinetics. MATERIALS AND METHODS: Drug-eluting beads (DEB; 100-300 microm and 700-900 microm) loaded with 37.5 mg doxorubicin per milliliter hydrated beads were used to embolize the hepatic artery feeding the left lobe of the liver in young adult Yucatan pigs (n = 5 per group). Control animals underwent embolization with bland beads (100-300 microm; n = 5). Systemic plasma levels of doxorubicin were measured and correlated to in vitro drug release. Blood sampling and histopathologic examination were performed during the 90-day follow-up. RESULTS: All animals underwent successful embolization, and the treatment was well tolerated. Mean volumes of beads administered were 2.0-3.4 mL, with mean doses of 127.5 mg and 78.7 mg of doxorubicin for the 100- to 300-microm and 700- to 900-microm DEB groups, respectively. Gross pathologic examination revealed no effects on organs other than the liver. There was a transient increase in liver enzyme levels, particularly in the groups of animals who underwent embolization with 100- to 300-microm DEB. Histopathologic study showed mostly nonnecrotic changes with bland beads, whereas the effects of DEB were more severe, with large areas of pannecrosis evident with the 100- to 300-microm DEB. Maximum plasma concentrations were 651 ng/mL and 42.8 ng/mL for the 100- to 300-microm and 700- to 900-microm DEB groups, respectively, observed at 1 minute for both groups. Correlation with in vitro data showed a strong linear relationship. CONCLUSIONS: Hepatic arterial embolization with DEB was shown to be safe and well tolerated. The locoregional delivery of doxorubicin from DEB caused targeted tissue damage with minimal systemic impact and could be a promising new approach to transarterial chemoembolization of solid tumors.     

MR imaging detection of superparamagnetic iron oxide loaded tris-acryl embolization microspheres

PURPOSE: To assess by magnetic resonance (MR) imaging the detectability of superparamagnetic iron oxide (SPIO)-labeled microspheres (MSs) in vitro on gelose, ex vivo in kidneys from embolized sheep, and in vivo in kidneys from embolized pigs. MATERIALS AND METHODS: With various sizes of SPIO-labeled MSs, common neck and pelvic spin-echo and gradient-echo sequences were acquired on a 1.5-T MR unit. SPIO-labeled MSs of four sizes were embedded in a hydrogel as single MSs or in multiple units, or multiplets. Detection rate on MR imaging was assessed according to the real size and number of MSs. SPIO-loaded and unloaded MSs of four sizes were injected into eight sheep kidneys, which underwent MR and pathologic examinations. For each size, the location of MSs in renal vasculature was determined and compared according to the technique used. Kidneys were embolized in pigs with various amounts of MSs in three sizes. MR was performed immediately after embolization and SPIO-labeled MS detection was assessed according to size, organ, and amount injected. Results SPIO-labeled MSs provide a low signal intensity on T1-weighted sequences, without distortion. In vitro, 28% of 100-300-microm single MSs were detected and more than 80% were detected for larger sizes. MS multiplets were all detected in all sizes. Ex vivo, all sizes of MSs were detected by MR imaging in kidneys, whereas control MSs were not observed. Histologic analysis showed that there was no difference in vascular distribution between SPIO-labeled MS and control MSs, and therefore for each caliber (P > .05). Arterial location of SPIO-labeled MSs was the same on MR imaging and histologic analysis. In vivo, SPIO-labeled MS were detected in the kidney vasculature when volumes greater than 1 mL of 100-300-microm or 500-700-microm MSs were injected. Volumes lower than 1 mL SPIO-labeled MSs were hardly detected in kidneys, regardless of MS size. Conclusions SPIO-labeled MSs are detected by MR imaging with common gradient-echo sequences in vitro in gelose and ex vivo and in vivo in kidneys. SPIO-labeled MSs could allow better control of embolization and thereby enhance efficacy and safety of the procedure.     

Hepatocellular carcinoma: long-term results of combined treatment with laser thermal ablation and transcatheter arterial chemoembolization

PURPOSE: To determine the potential long-term effectiveness of laser thermal ablation (LTA) followed by transcatheter arterial chemoembolization (TACE) in the percutaneous ablation of large hepatocellular carcinoma (HCC). MATERIALS AND METHODS: Thirty large HCCs 3.5-9.6 cm in diameter (mean diameter, 5.2 cm) and 15 small HCCs 0.8-3.0 cm (mean diameter, 1.9 cm) were treated with ultrasonographically guided LTA with TACE and with LTA alone, respectively, in 30 patients: 19 with a solitary large HCC, and 11 with one to three additional synchronous small HCCS: A 1.064-microm neodymium yttrium-aluminium-garnet (Nd-YAG) laser at a power of 5.0 W was coupled with one to four quartz optic fibers that were advanced through 21-gauge needles. Segmental TACE was performed 30-90 days after LTA. All lesions were evaluated for change in size at computed tomography (CT), alpha-fetoprotein (AFP) levels, recurrence rates, and cumulative survival rates. RESULTS: No major complications occurred in 127 LTA sessions. CT showed complete tumor necrosis in 27 (90%) of 30 large HCCS: Twenty-eight patients were followed up for 6-41 months (mean, 17.1 months). In 25 patients, all lesions appeared stable or smaller at CT. AFP levels decreased to the normal range in all patients with high pretreatment values. The 1-, 2-, and 3-year local recurrence rate was 7% in large HCCS: Complete tumor necrosis was achieved in all 15 (100%) small HCCs; none of them recurred locally. The 1-, 2-, and 3-year cumulative survival rates were 92%, 68%, and 40%, respectively. CONCLUSION: LTA followed by TACE is an effective palliative therapy in treating large HCCS:     

Sentinel node detection using contrast-enhanced power Doppler ultrasound lymphography

RATIONALE AND OBJECTIVES: To establish the feasibility of using contrast-enhanced interstitial ultrasound (US) lymphography as an alternative to current sentinel node detection methods. METHODS: Aqueous US contrast microbubble suspensions of varying diameter were evaluated in vitro to characterize response to insonation. Contrast media were then injected subcutaneously into the distal extremities of 11 normal dogs to target the cervical and popliteal lymph nodes (nodes, n = 40). First-order (sentinel) lymph nodes and second-order sublumbar nodes were imaged intermittently from 0 to at least 120 minutes following contrast injection using continuous power Doppler mode. Lymphoscintigraphy studies were performed on 4 dogs to verify lymphatic drainage patterns and sentinel lymph nodes. RESULTS: Contrast enhancement occurred in 34/40 (85%) sentinel nodes overall and in 30/32 (94%) nodes when submicron or near-micron diameter bubble formulations were used. In many instances, enhancement persisted throughout the imaging period. Contrast response was most pronounced using a high mechanical index and tissue artifact was reduced or eliminated when using a high pulse repetition frequency. CONCLUSIONS: Contrast-enhanced interstitial US lymphography could serve as an alternative to current sentinel node detection methods. Preliminary findings suggest that submicron or near-micron-diameter bubbles may be suitable for lymphatic imaging applications.     

Validating volume flow measurements from a novel semiautomated four-dimensional Doppler ultrasound scanner

RATIONALE AND OBJECTIVES: Accurate measurement of blood volume flow (in ml/min) is an important clinical goal. This project compared in vitro and in vivo volume flow measurements obtained with a novel, real-time three-dimensional (i.e., four-dimensional) ultrasound scanner (Encore PV; Vuesonix Sensors, Wayne, PA) with those from an invasive transit time flowmeter. MATERIALS AND METHODS: A flow pump was used to generate pulsatile flow rates from 60 to 600 ml/min. The Encore detected absolute blood velocity vectors within a volume. The scanner determined the centerline of the vessel and volume flow was then automatically calculated. Results were compared with those of an invasive technique for volumetric blood flow measurements utilizing a transit-time flowmeter (TS420; Transonic Systems Inc., Ithaca, NY). In vivo, 10 second datasets of the volume flow in the distal aorta of six rabbits were obtained simultaneously with the Encore PV and the flowmeter. Data were compared using linear regression and Bland-Altman analysis (due to the lack of independence). RESULTS: In vitro, Encore and flowmeter measurements both matched the flow pump (r2 > 0.99; P < .0001) with mean errors of -11.8% and -0.3%, respectively. Marked underestimation of the true flow rates was encountered with the Encore at the lowest pump setting. In vivo mean volume flows between 10.6 and 79.3 ml/min were measured. Mean and maximum volume flows obtained with the two techniques correlated significantly (P < .0001) with r2 values of 0.86 and 0.62, respectively. The corresponding root-mean-square errors were 6.9% for mean flow and 61.2% for maximum volume flow measurements. CONCLUSION: A new semiautomated four-dimensional Doppler device has been tested in vitro and in vivo. Mean volume flow measurements with this unit are comparable to those of an invasive flowmeter.     

MRI detection of macrophages labeled using micrometer-sized iron oxide particles

PURPOSE: To evaluate cellular labeling of immune cells using micron-sized iron oxide particles (MPIOs) and evaluate the MR relaxivity and MRI detection of the labeled cells. MATERIALS AND METHODS: Immune cells isolated from mice and rats were labeled with three different sizes of MPIO particles (0.35, 0.90, or 1.63 microm). These labeled cells were characterized using transmission electron microscopy (TEM), fluorescence microscopy, flow cytometry, MR relaxometry, and MRI. RESULTS: Macrophage uptake of MPIOs was found to be highest for the 1.63-microm size particles. MR relaxivity measurements indicated greater spin-spin relaxation for MPIO-labeled cells relative to cells labeled with nanometer-sized ultra-small superparamagnetic iron oxide (USPIO) particles with similar iron content. TEM and fluorescence microscopy indicated cellular uptake of multiple MPIO particles per cell. Macrophages labeled with 1.63-microm MPIOs had an average cellular iron uptake of 39.1 pg/cell, corresponding to approximately 35 particles per cell. CONCLUSION: Cells labeled with one or more MPIO particles could be readily detected ex vivo at 11.7 Tesla and after infusion of the MPIO-labeled macrophages into the kidney of a rat, hypointense regions of the outer cortex are observed, in vivo, by MRI at 4.7 Tesla.