Short Imaging Time Research Articles

Parallel imaging enhanced MR colonography using a phantom model

To compare various Array Spatial and Sensitivity Encoding Technique (ASSET)-enhanced T2W SSFSE (single shot fast spin echo) and T1-weighted (T1W) 3D SPGR (spoiled gradient recalled echo) sequences for polyp detection and image quality at MR colonography (MRC) in a phantom model. Limitations of MRC using standard 3D SPGR T1W imaging include the long breath-hold required to cover the entire colon within one acquisition and the relatively low spatial resolution due to the long acquisition time. Parallel imaging using ASSET-enhanced T2W SSFSE and 3D T1W SPGR imaging results in much shorter imaging times, which allows for increased spatial resolution. Using two porcine colon phantoms each with eight simulated 3-10-mm "polyps," baseline reference sequences acquired without ASSET (6-mm slices and readout bandwidth [BW] 62 kHz) were compared with 11 SSFSE and 8 SPGR sequences acquired with 2-fold ASSET acceleration. ASSET-enhanced SSFSE and SPGR sequences comprised BW/matrix combinations ranging from 20-62 kHz/256-352x256, respectively, with slice thicknesses adjusted from 3.0 to 4.5 mm to maintain a 23-26-second acquisition time and 30 cm slab thickness. Two experienced radiologists viewed the datasets in a randomized, blinded fashion. Compared to reference sequences, ASSET-enhanced SSFSE and SPGR sequences facilitated better polyp detection and had similar overall image quality and per-phantom specificity. The two best ASSET-enhanced SSFSE (3 and 4.5 mm slices, each with BW of 62.5 kHz and 352x256 matrices) and three best ASSET-enhanced SPGR BW/slice thickness/matrix combinations of 31 kHz/4.4 msec/192x256; 62/3.4/192x256; and 62/4.0/192x256, respectively, permitted detection of all polyps>or=5 mm. Parallel imaging using ASSET-enhanced T2W SSFSE and T1W 3D SPGR improves the ability to detect significant colon polyps in an MRC phantom model.

Sensitivity of diffusion weighted steady state free precession to anisotropic diffusion

Diffusion-weighted steady-state free precession (DW-SSFP) accumulates signal from multiple echoes over several TRs yielding a strong sensitivity to diffusion with short gradient durations and imaging times. Although the DW-SSFP signal is well characterized for isotropic, Gaussian diffusion, it is unclear how the DW-SSFP signal propagates in inhomogeneous media such as brain tissue. This article presents a more general analytical expression for the DW-SSFP signal which accommodates Gaussian and non-Gaussian spin displacement probability density functions. This new framework for calculating the DW-SSFP signal is used to investigate signal behavior for a single fiber, crossing fibers, and reflective barriers. DW-SSFP measurements in the corpus callosum of a fixed brain are shown to be in good agreement with theoretical predictions. Further measurements in fixed brain tissue also demonstrate that 3D DW-SSFP out-performs 3D diffusion weighted spin echo in both SNR and CNR efficiency providing a compelling example of its potential to be used for high resolution diffusion tensor imaging.

Analysis and Reproducibility of 3′-Deoxy-3′-[18F]Fluorothymidine Positron Emission Tomography Imaging in Patients with Non–Small Cell Lung Cancer

Imaging tumor proliferation with 3'-deoxy-3'-[(18)F]fluorothymidine (FLT) and positron emission tomography is being developed with the goal of monitoring antineoplastic therapy. This study assessed the methods to measure FLT retention in patients with non-small cell lung cancer (NSCLC) to measure the reproducibility of this approach. Nine patients with NSCLC who were untreated or had progressed after previous therapy were imaged twice using FLT and positron emission tomography within 2 to 7 days. Reproducibility (that is, error) was measured as the percent difference between the two patient scans. Dynamic imaging was obtained during the first 60 min after injection. Activity in the blood was assessed from aortic images and the fraction of unmetabolized FLT was measured. Regions of interest were drawn on the plane with the highest activity and the adjacent planes to measure standardized uptake value (SUV(mean)) and kinetic variables of FLT flux. We found that the SUV(mean) obtained from 30 to 60 min had a mean error of 3.6% (range, 0.6-6.9%; SD, 2.3%) and the first and second scans were highly correlated (r(2) = 0.99; P < 0.0001). Using shorter imaging times from 25 to 30 min or from 55 to 60 min postinjection also resulted in small error rates; SUV(mean) mean errors were 8.4% and 5.7%, respectively. Compartmental and graphical kinetic analyses were also fairly reproducible (r(2) = 0.59; P = 0.0152 and r(2) = 0.58; P = 0.0175 respectively). FLT imaging of patients with NSCLC was quite reproducible with a worst case SUV(mean) error of 21% when using a short imaging time.

MR fetography using heavily T2-weighted sequences: Comparison of thin- and thick-slab acquisitions

Purpose To evaluate the use of MR-fetography sequences in identifying the major fetal structures and to compare thick- and thin-slab acquisitions for their diagnostic value. Materials and methods Twenty-one consecutive, pregnant women with suspected fetal pathology underwent fetal magnetic resonance imaging (MRI) using a 1.5 T MRI unit. Heavily T2-weighted, single-shot fast spin-echo (SSFSE) sequences with a long echo train (MR-fetography) were acquired in a thick- and thin-slab modus. Thick- and thin-slab acquisitions were reviewed by two experienced radiologists with regard to the overall image quality and landmark anatomical structures (spinal canal, spinal cord, posterior fossa, cerebellum, brainstem, basal cisterns, stomach, urinary bladder and umbilical cord according to a three-scale grading system (good, moderate and poor). Visibility scores were calculated and compared between both sequences. Results Overall image quality was graded good in 76.2%, moderate in 19.0% and poor in 4.8% for thick-slab images and good in 81%, moderate in 14.3% and poor in 4.8% for thin-slab images. The visibility scores of the thick/thin-slab images for evaluation of the main fetal structures were as follows: for the spinal canal 2.8 ± 0.4/2.9 ± 0.54 ( p > 0.05), spinal cord 2.4 ± 0.75/2.7 ± 0.66 ( p > 0.05), posterior fossa components (cerebellum, brainstem and basal cisterns) 2.4 ± 0.68/2.8 ± 0.54; 2.4 ± 0.67/2.7 ± 0.66; 2.5 ± 0.51/2.7 ± 0.56 ( p < 0.05), stomach 2.8 ± 0.44/2.9 ± 0.48 ( p > 0.05), urinary bladder 2.8 ± 0.51/2.8 ± 0.54 ( p > 0.05) and umbilical cord 2.9 ± 0.30/2.6 ± 0.60 ( p < 0.05). Conclusion Heavily T2-weighted MR-fetography renders a quick overview of fetal contours, fetal position, amount of amniotic fluid and integrity and presence of several major fluid containing structures. Thick- and thin-slab acquisitions render complementary information. Thick-slab images display the entire fetus in one projection while thin-slab images provide more detailed anatomical information. The short imaging time usually allows measuring both thick- and thin-slab images. MR-fetography is as a helpful addition to conventional fetal MRI. MR-fetography should not be viewed as a single, stand alone sequence but as a supporting fast MR sequence in a well-designed multisequence fetal MRI protocol. Future studies evaluating larger patient groups are mandatory.

Antibiofouling polymer-coated gold nanoparticles as a contrast agent for in vivo x-ray computed tomography imaging

Current computed tomography (CT) contrast agents such as iodine-based compounds have several limitations, including short imaging times due to rapid renal clearance, renal toxicity, and vascular permeation. Here, we describe a new CT contrast agent based on gold nanoparticles (GNPs) that overcomes these limitations. Because gold has a higher atomic number and X-ray absorption coefficient than iodine, we expected that GNPs can be used as CT contrast agents. We prepared uniform GNPs (∼30 nm in diameter) by general reduction of HAuCl4 by boiling with sodium citrate. The resulting GNPs were coated with polyethylene glycol (PEG) to impart antibiofouling properties, which extends their lifetime in the bloodstream. Measurement of the X-ray absorption coefficient in vitro revealed that the attenuation of PEG-coated GNPs is 5.7 times higher than that of the current iodine-based CT contrast agent, Ultravist. Furthermore, when injected intravenously into rats, the PEG-coated GNPs had a much longer blood circulation ...

Parallel imaging of knee cartilage at 3 Tesla

To evaluate the feasibility and reproducibility of quantitative cartilage imaging with parallel imaging at 3T and to determine the impact of the acceleration factor (AF) on morphological and relaxation measurements. An eight-channel phased-array knee coil was employed for conventional and parallel imaging on a 3T scanner. The imaging protocol consisted of a T2-weighted fast spin echo (FSE), a 3D-spoiled gradient echo (SPGR), a custom 3D-SPGR T1rho, and a 3D-SPGR T2 sequence. Parallel imaging was performed with an array spatial sensitivity technique (ASSET). The left knees of six healthy volunteers were scanned with both conventional and parallel imaging (AF = 2). Morphological parameters and relaxation maps from parallel imaging methods (AF = 2) showed comparable results with conventional method. The intraclass correlation coefficient (ICC) of the two methods for cartilage volume, mean cartilage thickness, T1rho, and T2 were 0.999, 0.977, 0.964, and 0.969, respectively, while demonstrating excellent reproducibility. No significant measurement differences were found when AF reached 3 despite the low signal-to-noise ratio (SNR). The study demonstrated that parallel imaging can be applied to current knee cartilage quantification at AF = 2 without degrading measurement accuracy with good reproducibility while effectively reducing scan time. Shorter imaging times can be achieved with higher AF at the cost of SNR.

Three-dimensional Contrast-enhanced MR Angiography of Aortic Dissection: A Pictorial Essay

Aortic dissection is a catastrophic aortic disorder with high morbidity and mortality rates. Prognosis and treatment vary with different types of aortic dissection; therefore, prompt and accurate diagnosis is essential. Ultrasonography is widely available and can be used even in relatively unstable patients. However, it has limited diagnostic accuracy and cannot provide three-dimensional (3D) display images for treatment planning. Both computed tomographic (CT) angiography and 3D contrast material-enhanced magnetic resonance (MR) angiography can accurately demonstrate aortic dissection, with CT having the advantages of wider availability and shorter imaging times. However, contrast-enhanced MR angiography is more suitable in medically stable patients, does not involve nephrotoxic contrast agent or ionizing radiation, and offers greater ease and speed of postprocessing. In clinical practice, contrast-enhanced MR angiography can provide high-quality imaging data suitable for 3D reconstructions. It also has excellent spatial and contrast resolution and allows studies to be performed in multiple vascular phases, making it valuable for the diagnosis and classification of aortic dissection and in providing information that is helpful for treatment planning. Three-dimensional contrast-enhanced MR angiography with postprocessing is a fast, accurate, and noninvasive technique that may prove to be the optimal imaging modality in medically stable patients with aortic dissection.

Charge exchange of laser-produced ions in a pulsed gas jet

Results of an experiment on the interaction of laser-produced plasma with a pulsed gas jet are reported. A resonant charge-exchange pumping of the n=3 level of the C3+ ion was observed. A spatial structure of the region of intensive interaction was obtained by a short time imaging of filtered plasma radiation. According to independent probe measurements, the interaction was realized at densities of ions and gas particles in excess of 1016 cm-3. The obtained data provide a prospect for future experiments on laser gain in the EUV spectral range based on charge-exchange pumping of the C5+ ion.

High-concentration contrast media in neurological multidetector-row CT applications: implications for improved patient management in neurology and neurosurgery

Dynamic CT scanning after intravenous injection of iodine contrast medium (CM) was proposed in the very early days of CT. The goal was to characterize tissue by extracting information from the temporal course of enhancement. In the early 1980s, modeling algorithms were already described in the literature for the quantitative calculation of cerebral blood flow (CBF). However, cerebral applications suffered from the insufficient temporal resolution available at that time and the central nervous system was already seen primarily as an MRI domain. The renaissance of dynamic CT in neurological applications came in the middle of the 1990s with the introduction of thrombolytic therapy in acute stroke. With CT being the primary imaging modality, getting additional hemodynamic information from the same device without having to move the patient appeared attractive. Multimodal CT protocols allow a comprehensive diagnosis of the emergency stroke patient in less than 15 minutes by combining nonenhanced CT (NECT), perfusion CT (PCT) and CT angiography (CTA). Dynamic PCT can also render important information in patients with intraaxial brain tumors, allowing differentiation not only between lymphoma and glioma but also between low-grade and high-grade glioma by quantifying local cerebral blood volume (CBV) and permeability of the blood-brain barrier (BBB). However, even if a shorter imaging time permits a reduction in volume of CM, adequate total iodine levels must be preserved for dynamic CT applications. Increased concentrations of iodine are therefore helpful to obtain adequate total iodine levels for imaging.

MO‐D‐L100F‐04: Imaging With Distributed Source Arrays

While the vast majority of x‐ray imaging procedures use a single x‐ray source, a growing number require measurement of x‐ray transmission from different locations. These exams are generally performed by moving a single x‐ray source to many positions. Examples include computed tomography (CT) and tomosynthesis. At the same time, several technologies are now becoming more available that enable to construction of source arrays, i.e., a large number of sources that can be turned on in sequence. The purpose of this presentation is to explore the capabilities and benefits of imaging with these source arrays.In CT, small deflections of the x‐ray focal spot (on the order of a millimeter) have been used to improve data sampling. Multiple sources or much larger deflections (on the order of centimeters) in the axial direction can be quite useful for increasing the thickness of the imaging slab in a single scan while reducing cone beam artifacts. Distributing sources in the circumferential direction can dramatically reduce the mechanical rotation needed to obtain a complete data set and therefore can shorten the scan time. The recently introduced dual source CT system is the most recent incarnation in this direction. The limiting case is CT scanning with no mechanical rotation, as in electron beam CT. An array of sources separated in the circumferential direction can also be used to reduce the size of the detector array. This can lead to a reduction in detected x‐ray scatter and perhaps in the adoption of more advanced detector technologies. It also provides a reasonable method for optimization of the incident intensity distribution, thereby potentially reducing the dose to the patient while also tailoring the distribution of quantum noise across the image.In tomosynthesis, as in CT, measurements from different directions are used to produce tomographic information, albeit with imperfect spatial separation due to data insufficiency. Nonetheless, tomosynthesis can be powerful in many settings where obtaining complete CT data is difficult, and is gaining popularity. Data acquisition with mechanical motion of a single source is limiting both in the needed imaging time and in the number of projections that can be obtained. A small number of projections makes the blurring function (the “crosstalk” from one location to another from imperfect spatial separation) very discrete and potentially distracting to the viewer. Source arrays can be used to produce tomosynthesis images with very short imaging time and smooth blurring functions, both of which are preferred.Thus, there are significant benefits from the use of distributed sources. The author anticipates that these source arrays will become more widely adopted.Research sponsored by GE Healthcare.Educational Objectives:1. become familiar with the types of source arrays and their capabilities.2. understand the benefits of source arrays in computed tomography.3. understand the benefits of source arrays in tomosynthesis.

Antibiofouling Polymer-Coated Gold Nanoparticles as a Contrast Agent for in Vivo X-ray Computed Tomography Imaging

Current computed tomography (CT) contrast agents such as iodine-based compounds have several limitations, including short imaging times due to rapid renal clearance, renal toxicity, and vascular permeation. Here, we describe a new CT contrast agent based on gold nanoparticles (GNPs) that overcomes these limitations. Because gold has a higher atomic number and X-ray absorption coefficient than iodine, we expected that GNPs can be used as CT contrast agents. We prepared uniform GNPs ( approximately 30 nm in diameter) by general reduction of HAuCl4 by boiling with sodium citrate. The resulting GNPs were coated with polyethylene glycol (PEG) to impart antibiofouling properties, which extends their lifetime in the bloodstream. Measurement of the X-ray absorption coefficient in vitro revealed that the attenuation of PEG-coated GNPs is 5.7 times higher than that of the current iodine-based CT contrast agent, Ultravist. Furthermore, when injected intravenously into rats, the PEG-coated GNPs had a much longer blood circulation time (>4 h) than Ultravist (<10 min). Consequently, CT images of rats using PEG-coated GNPs showed a clear delineation of cardiac ventricles and great vessels. On the other hand, relatively high levels of GNPs accumulated in the spleen and liver, which contain phagocytic cells. Intravenous injection of PEG-coated GNPs into hepatoma-bearing rats resulted in a high contrast ( approximately 2-fold) between hepatoma and normal liver tissue on CT images. These results suggest that PEG-coated GNPs can be useful as a CT contrast agent for a blood pool and hepatoma imaging.

Multiple emulsion microbubbles for ultrasound imaging

In order to improve the sensitivity of ultrasound imaging, the contrast agents, a powerful non-invasive and real-time medical imaging technique, are used. However, air or N 2 or perfluorocarbon only encapsulated microbubbles which are currently used have lower efficiency and short imaging time. So the novel contrast agents with a higher efficiency are required. To achieve this objective, the strategy that we have explored involves the use of superparamagnetic iron oxide (SPIO) Fe 3O 4 nanoparticles multilayer emulsion microbubbles. This multilayer structure consists of three layers. The core is poly- d, l-lactide (PLA) encapsulated N 2 nanobubble with the SPIO nanoparticles forming oil-in-water (W/O) layer. The outermost is water-in-oil-in-water ((W/O)/W) emulsion layer with PVA solution. Herein we describe the synthesis and characterization of ultrasound imaging microstructure with an overall diameter of around 2μm–8μm. On the one hand, the stable gas encapsulated microstructure can provide a high scattering intensity resulting in high echogenicity, On the other hand, SPIO nanoparticles have shown the potential of high-resolution sonography. So the multiple emulsion microbubbles with SPIO can have double action to enhance the ultrasound imaging. Besides, because SPIO can also serve as magnetic resonance imaging (MRI) contrast agents, such microstructure may be useful for multimodality imaging studies in ultrasound imaging and MRI.

Update on radiological imaging of renal cell carcinoma

US is frequently used as the initial imaging in patients with suspected renal disease. US contrast agents offer the potential to increase the sensitivity in patients who cannot undergo CT or MTI. Harmonic imaging has helped with the evaluation of renal cystic lesions. CT remains the reference standard for staging and lesion characterization. The rapid technological advances mean that ultra-thin slices and 3D imaging have now become more widely available. MRI has also greatly advanced in speed and image quality, but at present, imaging time and scanner availability mean that MRI is generally used as a problem-solving tool. It is particularly helpful for smaller lesions and complex cystic lesions, where subtraction can be used to accurately identify the presence of enhancement. MRI is used as the primary diagnostic tool for patients with radiation concerns and those with renal failure. Caution must now also be taken in these patients, given the recent studies raising the association of gadolinium-based compounds and NSF. There have been dramatic improvements in renal imaging over the last decade, offering better resolution, shorter imaging times and better patient acceptance. The progress in minimally invasive techniques has driven the need to provide better preoperative information to the surgeon. The future of renal imaging is an exciting field; perhaps with fluorodeoxyglucose-based positron emission tomography we will be able to predict the biological behaviour of a tumour, and molecular imaging agents will become available to identify and hopefully treat specific tumour types.

Reduced field‐of‐view MRI using outer volume suppression for spinal cord diffusion imaging

A spin-echo single-shot echo-planar imaging (SS-EPI) technique with a reduced field of view (FOV) in the phase-encoding direction is presented that simultaneously reduces susceptibility effects and motion artifacts in diffusion-weighted (DW) imaging (DWI) of the spinal cord at a high field strength (3T). To minimize aliasing, an outer volume suppression (OVS) sequence was implemented. Effective fat suppression was achieved with the use of a slice-selection gradient-reversal technique. The OVS was optimized by numerical simulations with respect to T(1) relaxation times and B(1) variations. The optimized sequence was evaluated in vitro and in vivo. In simulations the optimized OVS showed suppression to <0.25% and approximately 3% in an optimal and worst-case scenario, respectively. In vitro measurements showed a mean residual signal of <0.95% +/- 0.42 for all suppressed areas. In vivo acquisition with 0.9 x 1.05 mm(2) in-plane resolution resulted in artifact-free images. The short imaging time of this technique makes it promising for clinical studies.

High-resolution/high-contrast MRI of human articular cartilage lesions

Background Magnetic resonance microscopy (MRM) is an important experimental tool in the identification of early cartilage lesions.Methods Normal and degenerated cartilage samples were imaged at 11.74 T using a standard spin echo sequence. Quantitative MR measurements for T1, T2, and ADC were obtained and mapping for T2 and ADC was performed. The bi-exponential model for T2 relaxation was also explored. Histology was carried out for comparison with MR images.Results MR images of cartilage samples displaying early stages of degeneration were positively correlated to their histological appearance in 23-μm high-resolu-tion images and also with much shorter imaging times at 47-μm resolution. T2 maps enable delineation of the actual cartilage zones, distinguishing the super?cial zone in particular. The bi-exponential model can reflect cartilage components at different stages of degeneration.Interpretation At 11.74 T, with 23-μm resolution or with 47-μm resolution and shorter imaging times, MRM provides images that allow visualization of early stages of cartilage degeneration, including super?cial ?brillation. This has not been shown previously. The images also allow quantitative measurements (T1, T2, and ADC) in each cartilage region, which can be indicative of different stages of cartilage degeneration.

Rapid fat suppression in MRI of the breast with short binomial pulses

To develop a faster method of fat suppression for use in dynamic contrast enhanced MRI of the breast. A method of fast fat suppression is presented using spatially nonselective rapid binomial pulses. In contrast to conventional binomial frequency-selective pulses, these short pulses are applied without interpulse delay, allowing for very rapid spectrally selective excitation. Effective water excitation and fat suppression were achieved in breast MRI at 3.0 Tesla with total excitation time as low as 160 microsec, which is several times shorter than the excitation time of currently used fat suppression techniques. Rapid fat suppression comes at the expense of increased specific absorption rate (SAR) and mildly degraded quality of suppression. A flexible tradeoff of short imaging time vs. SAR can be made to optimize imaging speed for fat-suppressed breast MRI. Rapid binomial pulses can be used for dynamic contrast enhanced breast MRI with excitation times significantly shorter than currently used fat suppression pulses. Shorter excitation time allows more rapid imaging, allowing greater temporal and spatial resolution for characterization of breast lesions.

Female Pelvis: MR Imaging at 3.0 T with Sensitivity Encoding and Flip-Angle Sweep Technique

This study had institutional review board approval; all 33 patients (mean age, 47 years +/- 16 [standard deviation]) gave informed consent. The aim was to prospectively evaluate the diagnostic image quality yielded by a 3.0-T T2-weighted turbo spin-echo magnetic resonance imaging sequence with a very short imaging time versus that yielded by a standard 3.0-T sequence at imaging of the female pelvis. Signal-to-noise ratio and delineation of gynecologic disorders were approximately equal between the two sequences. The majority of tissue contrasts were comparable, but contrast between fluid and muscle was significantly higher and motion artifacts were reduced (P < .001 for both) with the short imaging time sequence. The fast sequence maintained or improved image quality and thus seems to be advantageous for uncooperative patients.

Real Time Three‐Dimensional Echocardiography in Assessing Ventricular Septal Defects: An Echocardiographic‐Surgical Correlative Study

Two-dimensional echocardiography (2DE) enhanced by combining with color Doppler technology has significant limitations in providing precise quantitative information, geometric assumptions to calculate chamber volume, mass, and ejection fraction. Reconstructed three-dimensional echocardiographic (3DE) systems (from multiple cross-sectional echocardiographic scans) are still cumbersome and time-consuming. Real time 3DE (RT-3DE) with shorter imaging time than with 3D reconstruction techniques can obtain qualitative and quantitative information on heart disorders. Our purpose was to investigate the feasibility and potential value of RT-3DE as a means of accurately and quantitatively estimating the size of VSD to correlate with the surgical findings. 38 patients with VSD were examined with RT-3DE. 3D image database was postprocessed using TomTec echo 3D workstation. The results were compared with the results measured by 2 DE and surgical findings. RT-3DE produced novel views of VSD and improved quantification of the size of the defect. The sizes obtained from 3DE have equivalent correlation with surgical findings as diameter measured by 2DE (r = 0.89 vs r = 0.90). Good agreement between blinded observers was achieved by little interobserver variability. RT-3DE offers intraoperative visualization of VSD to generate a "virtual sense of depth" without extending examining time. From an LV en face projection, the positions, sizes, and shapes of VSDs can be accurately determined to permit quantitative recording of VSD dynamics. It is a potentially valuable clinical tool to provide precise imaging for surgical and catheter-based closure of difficult perimembranous and singular or multiple muscular VSD.

Gold nanoparticles: a new X-ray contrast agent

There have been few fundamental improvements in clinical X-ray contrast agents in more than 25 years, and the chemical platform of tri-iodobenzene has not changed. Current agents impose serious limitations on medical imaging: short imaging times, the need for catheterization in many cases, occasional renal toxicity, and poor contrast in large patients. This report is the first demonstration that gold nanoparticles may overcome these limitations. Gold has higher absorption than iodine with less bone and tissue interference achieving better contrast with lower X-ray dose. Nanoparticles clear the blood more slowly than iodine agents, permitting longer imaging times. Gold nanoparticles, 1.9 nm in diameter, were injected intravenously into mice and images recorded over time with a standard mammography unit. Gold biodistribution was measured by atomic absorption. Retention in liver and spleen was low with elimination by the kidneys. Organs such as kidneys and tumours were seen with unusual clarity and high spatial resolution. Blood vessels less than 100 microm in diameter were delineated, thus enabling in vivo vascular casting. Regions of increased vascularization and angiogenesis could be distinguished. With 10 mg Au ml(-1) initially in the blood, mouse behaviour was unremarkable and neither blood plasma analytes nor organ histology revealed any evidence of toxicity 11 days and 30 days after injection. Gold nanoparticles can be used as X-ray contrast agents with properties that overcome some significant limitations of iodine-based agents.

Clinical relevance of diffusion and perfusion magnetic resonance imaging in assessing intra-axial brain tumors

Advanced magnetic resonance (MR) imaging techniques provide physiologic information that complements the anatomic information available from conventional MR imaging. We evaluated the roles of diffusion and perfusion imaging for the assessment of grade and type of histologically proven intraaxial brain tumors. A total of 28 patients with intraaxial brain tumors underwent conventional MR imaging (T2- and T1-weighted sequences after gadobenate dimeglumine injection), diffusion imaging and T2*-weighted echo-planar perfusion imaging. Examinations were performed on 19 patients during initial diagnosis and on nine patients during follow-up therapy. Determinations of relative cerebral blood volume (rCBV) and apparent diffusion coefficient (ADC) were performed in the solid parts of each tumor, peritumoral region and contralateral white matter. For gliomas, rCBV values were greater in high-grade than in low-grade tumors (3.87+/-1.94 versus 1.30+/-0.42) at the time of initial diagnosis. rCBV values were increased in all recurrent tumors, except in one patient who presented with a combination of recurrent glioblastoma and massive radionecrosis on histology. Low-grade gliomas had low rCBV even in the presence of contrast medium enhancement. Differentiation between high- and low-grade gliomas was not possible using diffusion-weighted images and ADC values alone. In the peritumoral areas of untreated high-grade gliomas and metastases, the mean rCBV values were higher for high-grade gliomas (1.7+/-0.37) than for metastases (0.54+/-0.18) while the mean ADC values were higher for metastases. The rCBV values of four lymphomas were low and the signal intensity-time curves revealed a significant increase in signal intensity after the first pass of gadobenate dimeglumine. Diffusion and perfusion imaging, even with relatively short imaging and data processing times, provide important information for lesion characterization.