| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
|
|
|
|||||||
|
|||||||||
Experimental Studies |
1 From the Robarts Research Institute, Imaging Research Laboratories, PO Box 5015, 100 Perth Dr, London, Ontario, Canada N6A 5K8 (S.E.C., E.D., A.R.L., B.K.R.); the Department of Medical Biophysics, University of Western Ontario, London, Canada (S.E.C., B.K.R.); and the Schering Contrast Media Research Laboratories, Berlin, Germany (H.J.W.). Received April 2, 1999; revision requested May 21; revision received June 18; accepted August 10. Supported in part by grants from Schering Contrast Media Research Laboratories and the Medical Research Council of Canada (no. MT-14315). Address reprint requests to B.K.R. (brutt@irus.rri.on.ca).
 |
Abstract |
|---|
 TOP Abstract IntroductionMATERIALS AND METHODSRESULTSDISCUSSIONReferences |
|---|
MATERIALS AND METHODS: MR imaging at 0.5 T was performed in 37 rabbits before and after intravenous injection of a gadolinium-based blood pool contrast agent (SH L 643 A), superparamagnetic iron oxide blood pool agent (SH U 555 C), or gadopentetate dimeglumine. T1-weighted fast spoiled gradient-echo images from the renal arteries to below the iliac bifurcation were obtained. The aorta-to-tissue signal difference–to-noise ratio (SDNR) was measured over time.
RESULTS: Both blood pool agents yielded excellent demonstration of the rabbit abdominal aorta. At a dose of 0.1 mmol/kg, both provided a statistically significant increase in aorta-to-tissue SDNR in comparison with that achieved with gadopentetate dimeglumine (200% increase for SH L 643 A, 95% increase for SH U 555 C; P < .05). A 0.1 mmol/kg dose of SH L 643 A provided a 24% increase in SDNR relative to the increase with a 0.37 mmol/kg dose of gadopentetate dimeglumine. Time-dependent enhancement properties of the blood pool agents differed due to differences in elimination method.
CONCLUSION: Both blood pool agents were found to be promising contrast agents for 0.5-T MR angiography; however, their clinical applicability warrants further investigation. The gadolinium-based agent had several advantages over the iron oxide compound, including less T2* dephasing, lack of susceptibility artifacts, and fast renal elimination.
Index terms: Contrast media, comparative studies • Contrast media, experimental studies • Gadolinium • Iron • Magnetic resonance (MR), contrast media, 981.12943 • Magnetic resonance (MR), vascular studies, 981.129412, 981.12942, 981.12943
|
Introduction |
|---|
|
TOPAbstractIntroductionMATERIALS AND METHODSRESULTSDISCUSSIONReferences |
|---|
Equilibrium phase angiography may be necessary when imaging at lower field strengths, because of the need for longer imaging times to generate acceptable image quality. In this context, contrast agents that remain exclusively intravascular may have several advantages over currently used extracellular gadolinium-based agents. The possible advantages include higher T1 relaxivities, reduced interstitial diffusion, and decreased dose and injection requirements. These properties reduce the need for first-pass imaging, providing new possibilities for high-quality equilibrium phase MR angiography.
In this study, two experimental blood pool agents were investigated for equilibrium phase MR angiography at 0.5 T. These agents have specific properties that are advantageous for low-field-strength imaging. One agent, SH L 643 A (Gadomer-17; Schering, Berlin, Germany), is a recently developed gadolinium dendrimer, with molecules large enough to remain within the vascular space yet small enough to be freely filtered by means of glomerular filtration (5). This property allows SH L 643 A to avoid the long retention times seen with some other experimental gadolinium-based macromolecular contrast agents (6,7). For SH L 643 A, the peak T1 relaxivity occurs near 20 MHz (0.47 T).
The other contrast agent, SH U 555 C (Resovist-S; Schering), is a superparamagnetic iron oxide compound. Although iron oxide particles have potential for use as positive-enhancing blood pool agents for MR angiography because of their high T1 relaxivities (8–10), these agents also exhibit strong T2* (susceptibility) effects, which result in transverse dephasing and subsequent loss of signal. The small size of the iron oxide particles in SH U 555 C reduces the susceptibility effect, thereby providing a larger T1/T2* relaxivity ratio (11). Lower field strengths also minimize the effects of T2* dephasing, which suggests that the T1 relaxation properties of SH U 555 C would dominate over T2* relaxation effects at 0.5 T, a condition that may not hold at higher field strengths.
Given the widespread use of contrast-enhanced MR angiography, it is clear that the diagnostic potential of recently developed contrast agents for use at low-field-strength MR imaging should be examined. Therefore, the specific aim of this study was to evaluate and compare SH L 643 A and SH U 555 C for their potential use in equilibrium phase abdominal MR angiography at 0.5 T. An experimental rabbit model was used because these two agents are not approved or widely available for human use at present.
|
MATERIALS AND METHODS |
|---|
|
TOPAbstractIntroductionMATERIALS AND METHODSRESULTSDISCUSSIONReferences |
|---|
SH L 643 A has a T1/T2 relaxivity ratio of 18.7/29.0 L · mmol-1 · sec-1 in blood plasma at 20 MHz and 40°C. This contrast agent is a water soluble dendritic contrast agent that contains 24 gadolinium complexes at the surface of the dendrimer, which is similar to other polymeric agents (12,13). This compound is built from a central trimesoyl triamide core and 18 lysine residues, giving rise to a 24-mer polyamine. The 24 free amino groups are linked to a macrocyclic tetraazacyclododecanetetraacetic acid gadolinium chelate (5). SH L 643 A exhibits low toxicity and complete renal elimination, and results in rats (5) have shown that the median lethal dose of this agent is greater than 10 mmol of gadolinium per kilogram of body weight (mmol/kg). The actual molecular mass is 17 kd, but because of the globular shape of the molecule, the apparent molecular mass is 35 kd. This higher apparent molecular weight acts to delay diffusion into the interstitial space. For comparison, the extracellular contrast agent gadopentetate dimeglumine has a molecular mass of approximately 570 d and a T1 relaxivity of 5.1 L · mmol-1 · sec-1 in blood plasma at 20 MHz and 40°C. Thus, the relaxivity of SH L 643 A is 3.7 times that of gadopentetate dimeglumine at 0.5 T and normal body temperature.
SH U 555 C has a T1/T2 relaxivity ratio of 24.0/60.0 L · mmol-1 · sec-1 in blood plasma at 20 MHz and 40°C. This compound consists of an iron oxide core surrounded by a carboxydextran coating. SH U 555 C is a small-molecular-size subfraction of ferucarbotran (Resovist; Schering), and the smaller size provides a more beneficial T1/T2* ratio for positive enhancement. Ferucarbotran is currently undergoing clinical trials to assess its use for demonstration of focal liver lesions (14,15) and evaluation of cerebral blood volume (16). Although no data are currently available for SH U 555 C, the median lethal dose of ferucarbotran has been shown (17) to be in excess of 10 mmol/kg iron in rats. Ferucarbotran is eliminated from the blood stream by means of uptake by the liver and spleen (17). It is expected that SH U 555 C will exhibit toxicity and biologic distribution characteristics similar to those of ferucarbotran. The mean hydrodynamic size of SH U 555 C (including the hydrated dextran coating in an aqueous environment) is about 21 nm; however, the iron core is much smaller—less than 5 nm.
Table 1 summarizes the properties of each contrast agent at 0.47 and 2.0 T. Both SH L 643 A and SH U 555 C exhibit a higher T1 relaxivity at 0.47 T than at 2.0 T. The T1/T2 relaxivity ratio for SH U 555 C is much higher at 0.47 T than that at 2.0 T (more than a factor of four).
|
The rabbits were divided into dose groups of 0.015, 0.025, 0.05, or 0.1 mmol/kg of either SH L 643 A or SH U 555 C and 0.1 or 0.37 mmol/kg gadopentetate dimeglumine (Table 2). The doses were calculated per millimole of metal (gadolinium or iron).
|
In all cases, the contrast agent was delivered immediately before imaging by means of a bolus injection through a 22-gauge catheter placed in the ear vein. The bolus injection was followed by a flush with 5 mL of saline solution. Although a power injector was not used, care was taken to maintain the injection rate as constant as possible during administration of the contrast agent. The injection rate was estimated to be 1 mL/sec, which resulted in an injection duration of 1–3 seconds. The delay between injection and onset of MR imaging did not vary greatly between rabbits because a constant-velocity bed motion was used to advance the animal into the isocenter of the magnet immediately after injection. Therefore, the variability among rabbits of the delay between injection and imaging onset was estimated to be approximately 10 seconds.
MR Imaging
All MR imaging procedures were performed with a 0.5-T unit (Signa; GE Medical Systems, Milwaukee, Wis). A conventional gradient of 10 mT/m, a slew rate of 17 T · m-1 · sec-1, and a custom-built 12.5-cm-diameter quadrature birdcage radio-frequency coil were used. The same protocol was used regardless of the contrast agent administered. The rabbits were positioned to allow imaging of the vasculature from the renal arteries to below the iliac bifurcation. For contrast-enhanced MR angiography, coronal T1-weighted three-dimensional fast spoiled gradient-echo images (22/5 [repetition time msec/echo time msec], 60° flip angle, 20 x 15-cm field of view, 1-mm section thickness, 256 x 256 matrix, 0.78 x 0.78-mm in-plane resolution) were obtained once before injection of the contrast agent and then repeated 10 times in succession immediately after the injection. For the SH U 555 C study, data for two additional time points were collected at 20 and 30 minutes after injection. A total of 12 sections were obtained with an imaging time of 1 minute 11 seconds, sequential k-space mapping, superior-to-inferior readout direction, and flow compensation in the readout and section-selective directions.
Choice of Imaging Parameters
Flow compensation was used because our preliminary results indicated that flow compensation increased the signal-difference–to–noise ratio (SDNR) in the rabbit aorta (unpublished data). Flow compensation resulted in an increase in the echo time from 4.1 to 5.0 msec. The repetition time was chosen to be 22 msec so that the imaging time would be approximately 1 minute. This imaging time permitted the investigation of equilibrium phase imaging but also allowed the changes in SDNR over time to be monitored with sufficient temporal resolution. The echo time was chosen to be the minimum allowed echo time. This value was estimated to be substantially less than the T2* of blood at all contrast agent concentrations.
We investigated the feasibility of equilibrium phase MR angiography at 0.5 T. Arterial phase imaging was omitted for the following reasons: First, to achieve an adequate signal-to-noise ratio, the necessary imaging time at 0.5 T is longer than that at higher field strengths. Second, blood pool agents do not show a major improvement over currently used extracellular agents when used for arterial phase MR angiography; therefore, the net benefit of the use of blood pool agents would be more evident at lower field strengths, where equilibrium phase imaging may be necessary. Arterial phase imaging is dependent on such factors as correct bolus timing and cardiac output. The use of equilibrium phase MR angiography eliminated these variables, so a fair comparison of the two blood pool agents relative to the conventional agent could be undertaken.
Image Analysis: Time Response Study
For each contrast agent, maximum intensity projection images in the anterior-posterior direction were analyzed to determine the SDNR as a function of time after injection. In each rabbit, the same regions of interest were evaluated over time. The signal intensity of the aorta was measured by manually placing a rectangular region of interest in the center of the thoracic aorta. These regions of interest were carefully chosen to avoid partial volume and inflow effects. Signal intensity of tissue also was measured by choosing a small rectangular region of interest in tissue adjacent to the aorta. A relatively homogeneous area of tissue was selected to avoid inclusion of signal intensity from smaller blood vessels. A similar small rectangular region was placed in the air surrounding the rabbit; the SD of this region was used as a measure of noise on the image. For greatest consistency, all regions of interest were placed by one of the authors (S.E.C.). By using the values recorded from these three regions of interest, we calculated the SDNR as a function of time. The SDNR was defined with the following equation: SDNR = (SIaorta - SItissue)/SDair, where SIaorta and SItissue are the signal intensity of aorta and surrounding tissue, respectively, and SDair is the SD of noise in air.
Statistical Analysis
The unpaired Student t test was performed to test for significant differences in vessel SDNR between nonenenhanced and contrast-enhanced three-dimensional spoiled gradient-echo MR angiographic maximum intensity projection images. A test for equal variances was performed prior to the calculation of the t statistic to verify the validity of the application of the Student t test. A P value of less than .05 was indicative of a significant difference.
|
RESULTS |
|---|
|
TOPAbstractIntroductionMATERIALS AND METHODSRESULTSDISCUSSIONReferences |
|---|
minute. The time after injection of contrast agent was then determined by using the time from the start of imaging to the midpoint of each section acquisition (when the center of k space was crossed) plus 0.5 minute to account for the initial delay.
|
|
The SDNR for SH U 555 C–enhanced MR angiograms followed a similar trend to that for SH L 643 A–enhanced images for the 0.015, 0.025, and 0.05 mmol/kg dose groups (Fig 1b). In comparison, at the higher dose of 0.1 mmol/kg, SDNR increased with time for the first 10 minutes, then reached a plateau that lasted until 30 minutes after injection. At the first time point after injection, a significant increase in SDNR over baseline values was observed for all dose groups (P < .05) except the 0.015 mmol/kg group; there were only two rabbits in this latter group, so statistical significance was not achieved in this case.
The absolute values of the SDNRs after SH U 555 C administration were not as high as those measured after an equivalent dose of SH L 643 A. For example, the SDNR (± SD) from the first image acquired after injection of 0.1 mmol/kg of SH L 643 A was 46.8 ± 3.0, whereas the SDNR from the SH U 555 C images at the same dose and time was 29.9 ± 6.2. This equated to an SDNR increase for SH L 643 A–enhanced images of 56% over that for SH U 555 C–enhanced images. The maximum SDNR for SH U 555 C–enhanced images at a dose of 0.1 mmol/kg (34.7 ± 7.3) occurred at approximately 11 minutes after injection; this value was still 35% less than the maximum SDNR for SH L 643 A–enhanced images.
Numeric results for SDNR measurements are shown in Tables 3 and 4. Table 3 shows the SDNR for all contrast agents at the first time point after injection. Table 4 provides SDNR as a function of time for the blood pool contrast agents at the 0.l mmol/kg dose and for gadopentetate dimeglumine at the 0.37 mmol/kg dose.
|
|
|
|
|
|
Comparison of All Contrast Agents
Use of SH L 643 A and SH U 555 C at 0.1 mmol/kg resulted in much better MR angiograms than did use of gadopentetate dimeglumine at the same dose. With this imaging protocol, 0.1 mmol/kg gadopentetate dimeglumine was found to be inadequate for MR angiography in rabbits, although the same dose of SH L 643 A or SH U 555 C resulted in a higher aorta-to-tissue SDNR (Fig 3) and superior small-vessel demonstration due to higher T1 relaxivity and intravascular distribution. At a dose of 0.1 mmol/kg gadopentetate dimeglumine, the vessel-to-tissue SDNR was 15.4 ± 1.6. The vessel-to-tissue SDNRs for SH L 643 A and SH U 555 C (46.8 ± 3.0 and 29.9 ± 6.2, respectively) were significantly different from the SDNR of gadopentetate dimeglumine at the same dose (P < .05). This equated to SDNR increases of 200% and 95% for SH L 643 A and SH U 555 C, respectively.
|
minutes after injection), SH L 643 A at a dose of 0.1 mmol/kg had a 24% higher SDNR than did gadopentetate dimeglumine at a dose of 0.37 mmol/kg. When the dose of gadopentetate dimeglumine was increased to account for decreases in T1 relaxivity as compared with that of SH L 643 A, considerable background tissue enhancement was seen. At this dose, the extravasation of gadopentetate dimeglumine out of the vascular space simultaneously decreased the signal intensity of blood while it increased the enhancement of the surrounding tissue (Fig 4).
|
|
|
No adverse reactions occurred in any of the rabbits during or after imaging.
|
DISCUSSION |
|---|
|
TOPAbstractIntroductionMATERIALS AND METHODSRESULTSDISCUSSIONReferences |
|---|
Comparison of Blood Pool Contrast Agents
We investigated two experimental blood pool agents: SH L 643 A, a gadolinium-based paramagnetic compound, and SH U 555 C, an iron oxide–based superparamagnetic agent. Gadolinium- and iron oxide–based compounds differ substantially in several respects, including elimination pathways, duration of blood enhancement, T1/T2 relaxivity ratio, susceptibility, and chemical structure.
SH L 643 A has several advantages over SH U 555 C, such as higher achievable SDNR and decreased susceptibility artifacts. At an echo time such as that used in this study (5 msec), considerable dephasing will occur in the vicinity of iron oxide particles; this explains the higher vascular signal intensity at 0.5 T on SH L 643 A–enhanced MR angiograms despite the higher T1 relaxivity for SH U 555 C in comparison with that for SH L 643 A. The use of a shorter echo time would decrease this dephasing effect and should, therefore, improve the quality of the SH U 555 C MR angiograms.
Time Response
The quick decrease over time in SDNR with SH L 643 A enhancement can be attributed to fast glomerular filtration of this compound. Renal elimination prevents long-term retention within the body, a problem that has been noted with several other gadolinium-based macromolecular contrast agents, including gadolinium chelates bound to dextran (18), albumin (19), and polylysine (20,21). SH L 643 A exhibits relaxivities comparable to those of other macromolecular contrast agents despite being small enough to be subject to renal elimination. Note that rabbits have higher glomerular filtration rates than do humans; hence, the blood pool enhancement half-life would be expected to be longer in humans.
The sharp decrease over time in SDNR seen with SH L 643 A (Fig 1) is in contrast to that seen with a dose of 0.1 mmol/kg SH U 555 C, where the SDNR remains at a nearly constant level for up to 30 minutes. At this dose, the concentration of SH U 555 C in the bloodstream was such that signal intensity loss due to T2* dephasing balanced the signal intensity gain due to the reduction in blood T1. The larger iron oxide particles were subject to quick uptake by the reticuloendothelial system and were sequestered in the liver. The smaller iron oxide particles that remained in the circulation had a more beneficial T1/T2* relaxivity ratio, which resulted in a higher SDNR at later time points. The differences in time-response curves suggest that these two agents may differ in terms of their clinical applications.
Equilibrium Phase MR Angiography at Low Field Strength
MR angiography at lower field strengths can be difficult due to an inherently lower signal-to-noise ratio and poor suppression of background tissue owing to the lower T1 of tissues. These factors make arterial phase imaging difficult. To obtain an adequate signal-to-noise ratio and resolution, equilibrium phase imaging may be important, and it is in this setting that the benefits of blood pool contrast agents for low-field-strength MR imaging would be realized. By using postprocessing techniques that are currently under development, arterial-venous separation could be achieved. Extended enhancement of the blood pool would permit increased imaging time and allow acquisition of images with high spatial resolution. Several MR sequences could be performed sequentially without loss of signal intensity or background enhancement. Expanded anatomic coverage would be possible, which would result in imaging of multiple body regions with a single injection of the contrast agent. The administered dose would be kept to a minimum, which would decrease the risk of side effects.
Blood pool agents could prove to be particularly beneficial for help in the diagnosis of peripheral arterial diseases and for MR angiography of the coronary arteries, which require blood pool enhancement for several minutes after injection (7,22,23). The ability to increase imaging times with the use of blood pool contrast agents would allow acquisition of images with a sufficient signal-to-noise ratio, even at a low magnetic field strength, through the use of signal averaging and selection of an optimal repetition time and flip angle.
Equilibrium phase MR angiography requires longer imaging times than does arterial phase imaging; therefore, the issue of respiratory motion must be addressed. In our rabbit model, no respiratory motion artifacts were seen. For applications such as peripheral angiography, respiratory motion would not be a problem. In the future, these blood pool agents may be applied in MR imaging of the abdominal or coronary vasculature. If respiratory motion is a problem, respiratory gating and retrospective re-sorting or reacquisition of the data could be used to reduce these artifacts. Respiratory gating would increase the imaging time; again, the intravascular properties of blood pool agents would provide an advantage over extracellular gadolinium chelates.
In this study, the SDNR was used as a quantitative indicator of the quality of MR angiograms, whereas other factors (eg, demonstration of small vessels) were qualitatively assessed. To determine with greater accuracy the diagnostic efficacy of SH L 643 A and SH U 555 C, future studies should include investigation of the ability of these contrast agents to facilitate the accurate depiction of vascular abnormalities such as aneurysm, dissection, and stenosis. This study was limited in scope because it was restricted to a disease-free animal model; however, the results are still relevant. One of the advantages of contrast-enhanced MR angiography is that the technique is relative flow independent. Therefore, the presence of complex blood flow patterns, which might be expected in patients with vascular disease, probably will not be a major factor in determining the applicability of these agents. The high relaxivities of these contrast agents would faciliate their ability to help accurately depict vascular morphology.
Blood pool agents that are similar to SH L 643 A and SH U 555 C have been evaluated in humans; however, the agents described in this article have specific advantages for low-field-strength imaging when equilibrium phase MR angiography may be necessary to achieve an adequate signal-to-noise ratio. Recent studies (8) in humans have not addressed low-field-strength MR imaging, nor were the contrast agents used in these studies targeted for use at low field strength.
A commonly used field strength is 1.5 T. If equilibrium phase MR angiography is needed, a longer imaging time would be necessary at 0.5 T, as compared with that at 1.5 T, to obtain the same signal-to-noise ratio. For this reason, it can be speculated that the net advantages of the use of blood pool agents rather than extracellular agents may be greater when imaging at 0.5 T than when imaging at 1.5 T. SH L 643 A has a higher relaxivity at 0.5 T than at 1.5 T, which provides a second reason that the relative increase in MR angiographic quality may be higher with this agent at 0.5 T than at 1.5 T. The T1/T2 relaxivity ratio for SH U 555 C decreases substantially as field strength increases; therefore, SH U 555 C may act more as a T2* contrast agent at 1.5 T. Finally, one of the blood pool agents, SH L 643 A, has already been evaluated for MR angiographic applications at 1.5 T in a dog model (5).
Other Applications of Blood Pool Agents
MR imaging with SH L 643 A and SH U 555 C could be advantageous in situations where both arterial phase and venous phase imaging are important. For example, imaging of the blood supply to the liver requires demonstration of the hepatic artery, as well as the portal and hepatic veins. The contrast agent must pass through three capillary beds prior to reaching the hepatic vein; therefore, large doses of an extracellular contrast agent are necessary to counteract gadolinium extraction within the microvasculature (5).
Intravascular MR contrast agents may allow valuable information to be gained regarding capillary permeability, tissue perfusion, and blood volume. It is believed that benign and malignant tumors can be classified by demonstrating their vascularity and the integrity of the capillary membranes. Blood pool agents can help discriminate between benign and malignant canine breast tumors (24), demonstrate peritumoral vessels (25), and measure microvascular permeability (19). SH U 555 C may be advantageous for these types of studies, because high susceptibility during the first pass of the contrast agent could provide information about blood flow.Practical applications: Blood pool agents such as SH L 643 A and SH U 555 C offer important advantages over the extracellular agent gadopentetate dimeglumine at 0.5-T MR imaging, where equilibrium phase imaging may be required to achieve an adequate signal-to-noise ratio and spatial resolution.
SH L 643 A appeared to be the more promising of the two new blood pool agents that were evaluated in this study. SH L 643 A has several advantages over SH U 555 C, including higher SDNR due to lower T2* dephasing, lack of susceptibility artifacts, and fast renal elimination. The use of such new blood pool agents introduces the possibility of equilibrium phase MR angiography, which would make possible the collection of images with high spatial resolution for help in the diagnosis of vascular disease. The clinical applicability of intravascular contrast agents may extend beyond the imaging of vascular anatomy to include imaging sequences that allow acquisition of relevant information regarding blood volume, perfusion, microvascular permeability, or tumor characterization.
|
Acknowledgments |
|---|
|
Footnotes |
|---|
Abbreviation: SDNR = signal difference–to-noise ratio
Author contributions: Guarantors of integrity of entire study, S.E.C., B.K.R.; study concepts, all authors; study design, S.E.C., B.K.R., H.J.W.; definition of intellectual content, S.E.C., B.K.R., H.J.W.; literature research, S.E.C., B.K.R., H.J.W.; experimental studies, S.E.C., B.K.R., E.D., A.R.L.; data acquisition and analysis, S.E.C.; statistical analysis, S.E.C.; manuscript preparation, S.E.C.; manuscript editing, all authors; manuscript review, B.K.R., H.J.W., E.D., A.R.L.
|
References |
|---|
|
TOPAbstractIntroductionMATERIALS AND METHODSRESULTSDISCUSSIONReferences |
|---|
This article has been cited by other articles:
|
|
 |
|
  G. Korosoglou, S. Shah, E.-J. Vonken, W. D. Gilson, M. Schar, L. Tang, D. L. Kraitchman, R. C. Boston, D. E. Sosnovik, R. G. Weiss, et al. Off-Resonance Angiography: A New Method to Depict Vessels--Phantom and Rabbit Studies Radiology, September 9, 2008; (2008) 2491071706. [Abstract] [Full Text]
|
|
|
|
|
|
J. W. Lee, W. K. Moon, H.-J. Weinmann, S. J. Kim, J. H. Kim, S. H. Park, T. J. Kim, C. J. Yoon, Y. H. Kim, E. Y. Cho, et al. Contrast-enhanced MR Imaging of Postoperative Scars and VX2 Carcinoma in Rabbits: Comparison of Macromolecular Contrast Agent and Gadopentetate Dimeglumine Radiology, October 1, 2003; 229(1): 132 - 139. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
S. S. Lee, H. W. Goo, S. B. Park, C. H. Lim, G. Gong, J. B. Seo, and T.-H. Lim MR Imaging of Reperfused Myocardial Infarction: Comparison of Necrosis-Specific and Intravascular Contrast Agents in a Cat Model Radiology, March 1, 2003; 226(3): 739 - 747. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
B. L. Gerber, D. A. Bluemke, B. B. Chin, R. C. Boston, A. W. Heldman, J. A. C. Lima, and D. L. Kraitchman Single-Vessel Coronary Artery Stenosis: Myocardial Perfusion Imaging with Gadomer-17 First-Pass MR Imaging in a Swine Model of Comparison with Gadopentetate Dimeglumine Radiology, October 1, 2002; 225(1): 104 - 112. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
M. Taupitz, J. Schnorr, S. Wagner, C. Abramjuk, H. Pilgrimm, D. Kivelitz, T. Schink, J. Hansel, G. Laub, H. Hunigen, et al. Coronary MR Angiography: Experimental Results with a Monomer-stabilized Blood Pool Contrast Medium Radiology, January 1, 2002; 222(1): 120 - 126. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
T. Allkemper, C. Bremer, L. Matuszewski, W. Ebert, and P. Reimer Contrast-enhanced Blood-Pool MR Angiography with Optimized Iron Oxides: Effect of Size and Dose on Vascular Contrast Enhancement in Rabbits Radiology, May 1, 2002; 223(2): 432 - 438. [Abstract] [Full Text] [PDF]
|
|
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
| RADIOLOGY | RADIOGRAPHICS | RSNA JOURNALS ONLINE |
) SH L 643 A provided the highest SDNR. Vessel enhancement with SH L 643 A decreases monotonically over time, owing to fast renal elimination of this compound. (b) At 0.1 mmol/kg, SH U 555 C remains in the vasculature for a longer time because the iron oxide particles are primarily metabolized in the liver. 
= 0.05 mmol/kg, 
= 0.025 mmol/kg, x = 0.015 mmol/kg, error bars = SEM.
