Partition coefficients for gadolinium chelates in the normal myocardium: Comparison of gadopentetate dimeglumine and gadobenate dimeglumine

Purpose:

To evaluate the influence of contrast agents with different relaxivity on the partition coefficient (λ) and timing of equilibration using a modified Look‐Locker inversion recovery (MOLLI) sequence in cardiac magnetic resonance imaging (MRI).

Materials and Methods:

MOLLI was acquired in 20 healthy subjects (1.5T) at the mid‐ventricular short axis precontrast and 5, 10, 20, 25, and 30 minutes after administration of a bolus of 0.15 mmol/kg gadobenate dimeglumine (Gd‐BOPTA) (n = 10) or gadopentetate dimeglumine (Gd‐DTPA) (n = 10). T1 times were measured in myocardium and blood pool. λ was approximated by ΔR1_myocardium/ΔR1_blood. Values for Gd‐BOPTA and Gd‐DTPA were compared. Interobserver agreement was evaluated (intraclass correlation coefficient [ICC]).

Results:

T1 times of myocardium and blood pool (P < 0.001) and λ (0.42 ± 0.03 and 0.47 ± 0.04, respectively, P < 0.001; excluding 5 minutes for Gd‐BOPTA) were significantly lower for Gd‐BOPTA than Gd‐DTPA. The λ_(Gd‐DTPA) showed no significant variation between 5 and 30 minutes. The λ_(Gd‐BOPTA) values were significantly lower at 5 minutes compared to other times (0.38 vs. 0.42; P < 0.05). Interobserver agreement for λ values was excellent with Gd‐BOPTA (ICC = 0.818) and good for Gd‐DTPA (ICC = 0.631).

Conclusion:

The λ_(Gd‐BOPTA) values were significantly lower compared to λ_(Gd‐DTPA) at the same administered dose. Using Gd‐BOPTA, the equilibrium between myocardium and blood pool was not achieved at 5 minutes postcontrast. J. Magn. Reson. Imaging 2012;36:733–737. © 2012 Wiley Periodicals, Inc.     

Quantitative rapid steady state T1 magnetic resonance imaging for cerebral blood volume mapping in mice: Lengthened measurement time window with intraperitoneal Gd‐DOTA injection

This work demonstrates how the rapid steady state T₁ MRI technique for cerebral blood volume fraction (BVf) quantification can be used with intraperitoneal Gd‐DOTA injections in mice at 4.7 T. The peak signal amplitude after intravenous administration (0.7 mmol/kg) and the steady state signal amplitude reached 15 min after intraperitoneal administration (6 mmol/kg) in the same mice lead to equivalent BVf measures in the order of 0.02 in the brain. The resulting time window for BVf quantification is ≈30 min and allows for cerebral BVf mapping with increased spatial resolution or signal‐to‐noise ratio, or for monitoring functional BVf changes. A cerebral BVf increase of up to 25% induced by the vasodilator acetazolamide was observed, validating the vascular origin of the signal. The noninvasive and quantitative rapid steady state T₁ technique can be used in serial studies to evaluate new drugs or disease models, such as antiangiogenic therapies in tumors. Magn Reson Med, 2013. © 2012 Wiley Periodicals, Inc.     

Assessment of liver function in thioacetamide‐induced rat acute liver injury using an empirical mathematical model and dynamic contrast‐enhanced MRI with Gd‐EOB‐DTPA

Purpose:

To evaluate thioacetamide (TAA)‐induced acute liver injury in rats using an empirical mathematical model (EMM) and dynamic contrast‐enhanced magnetic resonance imaging (DCE‐MRI) with gadolinium ethoxybenzyl diethylenetriamine pentaacetic acid (Gd‐EOB‐DTPA).

Materials and Methods:

Eighteen rats were divided into three groups (normal control [n = 6], TAA [140] [n = 6], and TAA [280] groups [n = 6]). The rats of the TAA (140) and TAA (280) groups were intravenously injected with 140 and 280 mg/kg body weight (BW) of TAA, respectively, while those of the normal control group were intravenously injected with the same volume of saline. DCE‐MRI studies were performed using Gd‐EOB‐DTPA (0.025 mmol Gd/kg; 0.1 mL/kg BW) as the contrast agent 48 hours after TAA or saline injection. After the DCE‐MRI study, blood was sampled and serum aspartate aminotransferase (AST) and alanine aminotransferase (ALT) were measured. We calculated the rate of contrast uptake (α), the rate of contrast washout (β), the elimination half‐life of relative enhancement (RE) (T_1/2), the maximum RE (RE_max), and the time to (RE_max) (T_max) from time‐signal intensity curves using EMM.

Results:

The RE_max values in the TAA (140) groups and TAA (280) groups were significantly smaller than that in the normal control group. The T_max value in the TAA (280) group was significantly greater than that in the normal control group. The β value in the TAA (280) group was significantly smaller than those in the normal control and TAA (140) groups, whereas there were no significant differences in β among groups. The T_1/2 value in the TAA (280) group was significantly greater than those in the normal control and TAA (140) groups. The RE_max, T_max, β, and T_1/2 values significantly correlated with AST and ALT.

Conclusion:

The EMM is useful for evaluating TAA‐induced acute liver injury using DCE‐MRI with Gd‐EOB‐DTPA. J. Magn. Reson. Imaging 2012; 36:1483–1489. © 2012 Wiley Periodicals, Inc.     

Comparison of the high relaxivity Gd chelates P1152 and Gd‐BOPTA for contrast‐enhanced MR angiography in rabbits at 1.5 Tesla and 3.0 Tesla

Purpose:

To compare signal‐enhancing properties of the high relaxivity Gd chelates P1152 and Gd‐BOPTA for contrast‐enhanced MR angiography (CE‐MRA) in rabbits at 1.5 Tesla (T) and 3.0T.

Materials and Methods:

Three‐dimensional CE‐MRA of the abdominal vasculature was performed in six rabbits using both contrast agents at a dose of 0.1 mmol/kg. Data acquisition was carried out during first pass and up to 10 min after contrast material administration. CNR was determined in aorta, vena cava, and renal cortex. Image quality (5‐point scale, 5 = best) of first pass MR angiograms was rated by two radiologists.

Results:

During first pass CNR of the aorta was 55.1 ± 5.8 (P1152) and 40.3 ± 3.9 (Gd‐BOPTA) at 1.5T (P < 0.05), and 114.9 ± 9.9 (P1152) and 73.5 ± 8.1 (Gd‐BOPTA) at 3.0T (P < 0.05). Both contrast agents showed a comparable decline of CNR within 10 min. Image quality was rated 4.8 ± 0.40 (P1152) and 4.5 ± 0.50 (Gd‐BOPTA) at 1.5T (P = 0.17), and 4.8 ± 0.37 (P1152) and 4.7 ± 0.47 (Gd‐BOPTA) at 3.0T (P = 0.61).

Conclusion:

The high relaxivity Gd‐chelate P1152 offers potential to improve image contrast for CE‐MRA compared with a clinically approved high relaxivity contrast agent. J. Magn. Reson. Imaging 2010;32:459–465. © 2010 Wiley‐Liss, Inc.     

Improved vessel delineation in keyhole time‐resolved contrast‐enhanced MR angiography using a gadolinium doped flush

Purpose

To prospectively assess the influence of a gadolinium doped saline flush compared with a pure saline flush on the image quality of the supra‐aortic vessels using time‐resolved contrast‐enhanced MR angiography (4D CE‐MRA) in a randomized double blind clinical trial.

Materials and Methods

Twenty‐two patients scheduled for contrast‐enhanced craniocerebral MRI underwent a supplemental 4D CE‐MRA covering the carotids to the superior sinus consisting of 30 dynamics of a T1‐weighted 3D gradient‐echo sequence (FFE) in sagittal direction. The temporal resolution of 1.1 s per dataset was achieved using the keyhole technique with the reference scan acquired at the end. Immediately after the intravenous (IV) injection of 0.1 mmol Gd/kg body weight of gadoterate, our patients received a 50‐mL flush consisting either of a 0.9% saline solution (n = 11) or doped with 50 mM gadolinium (n = 11; total Gd: 0.11 mmol/kg) at a flow‐rate of 2 mL/s. Vessel delineation, image quality, signal‐to‐noise‐ (SNR) and contrast‐to‐noise (CNR) ratios over time were compared.

Results

Both vessel delineation (internal carotid artery [ICA]: slope_saline = 308.5; slope_Gd = 528.9; P = 0.006; superior sagittal sinus [SSS]: slope_saline = 505.3; slope_Gd = 674.9; P = 0.007) and CNR (ICA: CNR_saline = 57.3; CNR_Gd = 80.55; P = 0.0417; SSS: CNR_saline = 74.15; CNR_Gd = 117.4; P = 0.0331) of the ICA and SSS were significantly increased using the gadolinium doped flush.

Conclusion

A low concentrated gadolinium flush in comparison to a pure saline flush improves significantly vessel contrast and their delineation in time‐resolved CE‐MRA using the keyhole technique. J. Magn. Reson. Imaging 2009;29:1147–1153. © 2009 Wiley‐Liss, Inc.     

Spin‐locked balanced steady‐state free‐precession (slSSFP)

A spin‐locked balanced steady‐state free‐precession (slSSFP) pulse sequence is described that combines a balanced gradient‐echo acquisition with an off‐resonance spin‐lock pulse for fast MRI. The transient and steady‐state magnetization trajectory was solved numerically using the Bloch equations and was shown to be similar to balanced steady‐state free‐precession (bSSFP) for a range of T₂/T₁ and flip angles, although the slSSFP steady‐state could be maintained with considerably lower radio frequency (RF) power. In both simulations and brain scans performed at 7T, slSSFP was shown to exhibit similar contrast and signal‐to‐noise ratio (SNR) efficiency to bSSFP, but with significantly lower power. Magn Reson Med, 2009. © 2009 Wiley‐Liss, Inc.     

High‐resolution magnetic resonance angiography in the mouse using a nanoparticle blood‐pool contrast agent

High‐resolution magnetic resonance angiography is already a useful tool for studying mouse models of human disease. Magnetic resonance angiography in the mouse is typically performed using time‐of‐flight contrast. In this work, a new long‐circulating blood‐pool contrast agent—a liposomal nanoparticle with surface‐conjugated gadolinium (SC‐Gd liposomes)—was evaluated for use in mouse neurovascular magnetic resonance angiography. A total of 12 mice were imaged. Scan parameters were optimized for both time‐of‐flight and SC‐Gd contrast. Compared to time‐of‐flight contrast, SC‐Gd liposomes (0.08 mmol/kg) enabled improved small‐vessel contrast‐to‐noise ratio, larger field of view, shorter scan time, and imaging of venous structures. For a limited field of view, time‐of‐flight and SC‐Gd were not significantly different; however, SC‐Gd provided better contrast‐to‐noise ratio when the field of view encompassed the whole brain (P < 0.001) or the whole neurovascular axis (P < 0.001). SC‐Gd allowed acquisition of high‐resolution magnetic resonance angiography (52 × 52 × 100 micrometer³ or 0.27 nL), with 123% higher (P < 0.001) contrast‐to‐noise ratio in comparable scan time (～45 min). Alternatively, SC‐Gd liposomes could be used to acquire high‐resolution magnetic resonance angiography (0.27 nL) with 32% higher contrast‐to‐noise ratio (P < 0.001) in 75% shorter scan time (12 min). Magn Reson Med, 2009. © 2009 Wiley‐Liss, Inc.     

Quantitative measurement of blood‐brain barrier permeability in human using dynamic contrast‐enhanced MRI with fast T1 mapping

Breakdown of the blood‐brain barrier (BBB), occurring in many neurological diseases, has been difficult to measure noninvasively in humans. Dynamic contrast‐enhanced magnetic resonance imaging measures BBB permeability. However, important technical challenges remain and normative data from healthy humans is lacking. We report the implementation of a method for measuring BBB permeability, originally developed in animals, to estimate BBB permeability in both healthy subjects and patients with white matter pathology. Fast T₁ mapping was used to measure the leakage of contrast agent Gadolinium diethylene triamine pentaacetic acid (Gd‐DTPA) from plasma into brain. A quarter of the standard Gd‐DTPA dose for dynamic contrast‐enhanced magnetic resonance imaging was found to give both sufficient contrast‐to‐noise and high T₁ sensitivity. The Patlak graphical approach was used to calculate the permeability from changes in 1/T₁. Permeability constants were compared with cerebrospinal fluid albumin index. The upper limit of the 95% confidence interval for white matter BBB permeability for normal subjects was 3 × 10^?4 L/g min. MRI measurements correlated strongly with levels of cerebrospinal fluid albumin in those subjects undergoing lumbar puncture. Dynamic contrast‐enhanced magnetic resonance imaging with low dose Gd‐DTPA and fast T₁ imaging is a sensitive method to measure subtle differences in BBB permeability in humans and may have advantages over techniques based purely on the measurement of pixel contrast changes. Magn Reson Med, 2010. © 2010 Wiley‐Liss, Inc.     

Quantitative contrast‐enhanced perfusion measurements of the human lung using the prebolus approach

Purpose

To investigate dynamic contrast‐enhanced MRI (DCE‐MRI) for quantification of pulmonary blood flow (PBF) and blood volume (PBV) using the prebolus approach and to compare the results to the global lung perfusion (GLP).

Materials and Methods

Eleven volunteers were examined by applying different contrast agent doses (0.5, 1.0, 2.0, and 3.0 mL gadolinium diethylene triamine pentaacetic acid [Gd‐DTPA]), using a saturation‐recovery (SR) true fast imaging with steady precession (TrueFISP) sequence. PBF and PBV were determined for single bolus and prebolus. Region of interest (ROI) evaluation was performed and parameter maps were calculated. Additionally, cardiac output (CO) and lung volume were determined and GLP was calculated as a contrast agent–independent reference value.

Results

The prebolus results showed good agreement with low‐dose single‐bolus and GLP: PBF (mean ± SD in units of mL/minute/100 mL) = single bolus 190 ± 73 (0.5‐mL dose) and 193 ± 63 (1.0‐mL dose); prebolus 192 ± 70 (1.0–2.0‐mL dose) and 165 ± 52 (1.0–3.0‐mL dose); GLP (mL/minute/100 mL) = 187 ± 34. Higher single‐bolus resulted in overestimated values due to arterial input function (AIF) saturation.

Conclusion

The prebolus approach enables independent determination of appropriate doses for AIF and tissue signal. Using this technique, the signal‐to‐noise ratio (SNR) from lung parenchyma can be increased, resulting in improved PBF and PBV quantification, which is especially useful for the generation of parameter maps. J. Magn. Reson. Imaging 2009;30:104–111. © 2009 Wiley‐Liss, Inc.     

Comparison of wideband steady‐state free precession and T2‐weighted fast spin echo in spine disorder assessment at 1.5 and 3 T

Wideband steady‐state free precession (WB‐SSFP) is a modification of balanced steady‐state free precession utilizing alternating repetition times to reduce susceptibility‐induced balanced steady‐state free precession limitations, allowing its use for high‐resolution myelographic‐contrast spinal imaging. Intertissue contrast and spatial resolution of complete‐spine‐coverage 3D WB‐SSFP were compared with those of 2D T₂‐weighted fast spin echo, currently the standard for spine T₂‐imaging. Six normal subjects were imaged at 1.5 and 3 T. The signal‐to‐noise ratio efficiency (SNR per unit‐time and unit‐volume) of several tissues was measured, along with four intertissue contrast‐to‐noise ratios; nerve‐ganglia:fat, intradural‐nerves:cerebrospinal fluid, nerve‐ganglia:muscle, and muscle:fat. Patients with degenerative and traumatic spine disorders were imaged at both MRI fields to demonstrate WB‐SSFP clinical advantages and disadvantages. At 3 T, WB‐SSFP provided spinal contrast‐to‐noise ratios 3.7–5.2 times that of fast spin echo. At 1.5 T, WB‐SSFP contrast‐to‐noise ratio was 3–3.5 times that of fast spin echo, excluding a 1.7 ratio for intradural‐nerves:cerebrospinal fluid. WB‐SSFP signal‐to‐noise ratio efficiency was also higher. Three‐dimensional WB‐SSFP disadvantages relative to 2D fast spin echo are reduced edema hyperintensity, reduced muscle signal, and higher motion sensitivity. WB‐SSFP's high resolution and contrast‐to‐noise ratio improved visualization of intradural nerve bundles, foraminal nerve roots, and extradural nerve bundles, improving detection of nerve compression in radiculopathy and spinal‐stenosis. WB‐SSFP's high resolution permitted reformatting into orthogonal planes, providing distinct advantages in gauging fine spine pathology. Magn Reson Med, 2012. © 2012 Wiley Periodicals, Inc.     

Imaging iron‐loaded mouse glioma tumors with bSSFP at 3 T

The poor prognosis for patients with high‐grade glioma is partly due to the invasion of tumor cells into surrounding brain tissue. The goal of the present work was to develop a mouse model of glioma that included the potential to track cell invasion using MRI by labeling GL261 cells with iron oxide contrast agents prior to intracranial injection. Two types of agents were compared with several labeling schemes to balance between labeling with sufficient iron to curb the dilution effect of cell division while avoiding overwhelming signal loss that could prevent adequate visualization of tumor boundaries. The balanced steady‐state free precession (bSSFP) pulse sequence was evaluated for its suitability for imaging glioma tumors and compared to T₂‐weighted two‐dimensional fast spin echo (FSE) and T₁‐weighted spoiled gradient recalled echo (SPGR) at 3 T in terms of signal‐to‐noise ratio and contrast‐to‐noise ratio efficiencies. Ultimately, a three‐dimensional bSSFP protocol consisting of a set of two images with complementary contrasts was developed, allowing excellent tumor visualization with minimal iron contrast when using pulse repetition time = 6 ms and α = 40°, and extremely high sensitivity to iron when using pulse repetition time = 22 ms and α = 20°. Quantitative histologic analysis validated that the strong signal loss seen in balanced steady state free precession pulse sequence images of iron‐loaded tumors correlated well with the presence of iron. Magn Reson Med, 2010. © 2010 Wiley‐Liss, Inc.     

Gadoxetic acid disodium-enhanced magnetic resonance imaging for biliary and vascular evaluations in preoperative living liver donors: comparison with gadobenate dimeglumine-enhanced MRI

Purpose

To compare gadoxetic acid disodium (Gd‐EOB‐DTPA)‐enhanced magnetic resonance imaging (MRI) with gadobenate dimeglumine (Gd‐BOPTA)‐enhanced MRI in preoperative living liver donors for the evaluation of vascular and biliary variations.

Materials and Methods

Sixty‐two living liver donors who underwent preoperative MRI were included in this study. Thirty‐one patients underwent MRI with Gd‐EOB‐DTPA enhancement, and the other 31 underwent MRI with Gd‐BOPTA enhancement. Two abdominal radiologists retrospectively reviewed dynamic T1‐weighted and T1‐weighted MR cholangiography images and ranked overall image qualities for the depiction of the hepatic artery, portal vein, hepatic vein, and bile duct on a 5‐point scale and determined the presence and types of normal variations in each dynamic phase. Semiquantitative analysis for bile duct visualization was also conducted by calculating bile duct‐to‐liver contrast ratios.

Results

No statistical differences were found between the two contrast media in terms of hepatic artery or bile duct image quality by the two reviewers, or in terms of portal vein image quality by one reviewer (P > 0.05). Gd‐BOPTA provided better image qualities than Gd‐EOB‐DTPA for the depiction of hepatic veins by both reviewers, and for the depiction of portal veins by one reviewer (P < 0.01). The two contrast media‐enhanced images had similar bile duct‐to‐liver contrast ratios (P > 0.05). Regarding diagnostic accuracies with hepatic vascular/biliary branching types, no significant differences were observed between the two contrast media (P > 0.05).

Conclusion

Gd‐EOB‐DTPA could be as useful as Gd‐BOPTA for the preoperative evaluation of living liver donors, and has the advantage of early hepatobiliary phase image acquisition. J. Magn. Reson. Imaging 2011;33:149–159. © 2010 Wiley‐Liss, Inc.     

On the measurement of absolute cerebral blood volume (CBV) using vascular‐space‐occupancy (VASO) MRI

Recently, a vascular‐space‐occupancy (VASO) MRI technique was developed for quantitative assessment of cerebral blood volume (CBV). This method uses the T₁‐shortening effect of gadolinium diethylenetriamine pentaacetic acid (Gd‐DTPA) with imaging parameters chosen that null the precontrast blood magnetization but allow the postcontrast blood magnetization to recover to equilibrium. A key advantage of VASO CBV estimation is that it provides a straightforward procedure for converting MR signals to absolute physiologic values. However, as with other T₁‐based steady‐state approaches, several important factors need to be considered that influence the accuracy of CBV values obtained with VASO MRI. Here, the transverse relaxation (T₂/T) effect in VASO MRI was investigated using multiecho spin‐echo and gradient‐echo experiments, resulting in underestimation of CBV by 14.9% ± 1.1% and 16.0% ± 2.5% for spin echo (TE = 10 ms) and gradient echo (TE = 6 ms), respectively. In addition, the influence of contrast agent clearance was studied by acquiring multiple postcontrast VASO images at 2.2‐min intervals, which showed that the concentration of Gd‐DTPA in the first 14 min (single dose) was sufficient for the blood magnetization to fully recover to equilibrium. Finally, the effect of vascular Gd‐DTPA leakage was assessed for scalp tissue, and signal extrapolation as a function of postinjection time was demonstrated to be useful in minimizing the associated errors. Specific recommendations for VASO MRI acquisition and processing strategies are provided. Magn Reson Med, 2009. © 2008 Wiley‐Liss, Inc.     

High‐resolution magnetic resonance colonography and dynamic contrast‐enhanced magnetic resonance imaging in a murine model of colitis

Inflammatory bowel disease, including ulcerative colitis, is characterized by persistent or recurrent inflammation and can progress to colon cancer. Colitis is difficult to detect and monitor noninvasively. The goal of this work was to develop a preclinical imaging method for evaluating colitis. Herein, we report improved MRI methods for detecting and characterizing colitis noninvasively in mice, using high‐resolution in vivo MR images and dynamic contrast‐enhanced MRI studies, which were confirmed by histologic studies in a murine model of colitis. C57Bl6/J male mice were treated with 2.5% dextran sulfate sodium in their drinking water for 5 days to induce colitis. MR images were acquired using a 9.4‐T Bruker scanner from 5–25 days following dextran sulfate sodium treatment. In dynamic contrast‐enhanced MRI studies, Gd uptake (K^trans) and its distribution (v_e) were measured in muscle and normal and inflamed colons after administering Gd‐diethyltriaminepentaacetic acid (Gd‐DTPA). T₂‐weighted MR images distinguished normal colon from diffusely thickened colonic wall occurring in colitis (P <0.0005) and correlated with histologic features. Values of K^trans and v_e obtained from dynamic contrast‐enhanced MRI were also significantly different in inflamed colons compared to normal colon (P < 0.0005). The results demonstrate that both T₂‐weighted anatomic imaging and quantitative analysis of dynamic contrast‐enhanced MRI data can successfully distinguish colitis from normal colon in mice. Magn Reson Med 63:922–929, 2010. © 2010 Wiley‐Liss, Inc.     

Comparison of intravascular and extracellular contrast media for absolute quantification of myocardial rest-perfusion using high-resolution MRI

Purpose:

To use the contrast agent gadofosveset for absolute quantification of myocardial perfusion and compare it with gadobenate dimeglumine (Gd‐BOPTA) using a high‐resolution generalized autocalibrating partially parallel acquisition (GRAPPA) sequence.

Materials and Methods:

Ten healthy volunteers were examined twice at two different dates with a first‐pass perfusion examination at rest using prebolus technique. We used a 1.5 T scanner and a 32 channel heart‐array coil with a steady‐state free precession (SSFP) true fast imaging with steady state precession (trueFISP) GRAPPA sequence (acceleration‐factor 3). Manual delineation of the myocardial contours was performed and absolute quantification was performed after baseline and contamination correction. At the first appointment, 1cc/4cc of the extracellular contrast agent Gd‐BOPTA were administered, on the second date, 1cc/4cc of the blood pool contrast agent (CA) gadofosveset. At each date the examination was repeated after a 15‐minute time interval.

Results:

Using gadofosveset perfusion the value (in cc/g/min) at rest was 0.66 ± 0.25 (mean ± standard deviation) for the first, and 0.55 ± 0.24 for the second CA application; for Gd‐BOPTA it was 0.62 ± 0.25 and 0.45 ± 0.23. No significant difference was found between the acquired perfusion values. The apparent mean residence time in the myocardium was 23 seconds for gadofosveset and 19.5 seconds for Gd‐BOPTA. Neither signal‐to‐noise ratio (SNR) nor subjectively rated image contrast showed a significant difference.

Conclusion:

The application of gadofosveset for an absolute quantification of myocardial perfusion is possible. Yet the acquired perfusion values show no significant differences to those determined with Gd‐BOPTA, maintained the same SNR and comparable perfusion values, and did not picture the expected concentration time‐course for an intravasal CA in the first pass. J. Magn. Reson. Imaging 2011;33:1047–1051. © 2011 Wiley‐Liss, Inc.     

Contrast‐enhanced specific absorption rate‐efficient 3D cardiac cine with respiratory‐triggered radiofrequency gating

Purpose:

To investigate the use of radiofrequency (RF) gating in conjunction with a paramagnetic contrast agent to reduce the specific absorption rate (SAR) and increase the blood‐myocardium contrast in balanced steady‐state free precession (bSSFP) 3D cardiac cine.

Materials and Methods:

RF gating was implemented by synchronizing the RF‐excitation with an external respiratory sensor (bellows), which could additionally be used for respiratory gating. For reference, respiratory‐gated 3D cine images were acquired without RF gating. Free‐breathing 3D cine images were acquired in eight healthy subjects before and after contrast injection (Gd‐BOPTA) and compared to breath‐hold 2D cine.

Results:

RF‐gated 3D cine reduced the SAR by nearly 40% without introducing significant artifacts while providing left ventricle (LV) measurements similar to those obtained with 2D cine. The contrast‐to‐noise ratio (CNR) was significantly higher for 3D cine compared to 2D cine, both before and after contrast injection; however, no statistically significant CNR increase was observed for the postcontrast 3D cine compared to the precontrast acquisitions.

Conclusion:

Respiratory‐triggered RF gating significantly reduces SAR in 3D cine acquisitions, which may enable a more widespread clinical use of 3D cine. Furthermore, CNR of 3D bSSFP cine is higher than of 2D and administration of Gd‐BOPTA does not improve the CNR of 3D cine. J. Magn. Reson. Imaging 2013;37:986–992. © 2012 Wiley Periodicals, Inc.     

Dynamic contrast‐enhanced MRI in ovarian cancer: Initial experience at 3 tesla in primary and metastatic disease

The aim of this study was to develop and demonstrate a methodology for dynamic contrast‐enhanced MRI at 3 T in patients with advanced ovarian cancer and to report the results from pharmacokinetic modeling of the data. Nineteen patients with suspected advanced ovarian carcinoma (FIGO stage 3 or higher) were enrolled in this prospective study. Up to three marker lesions were identified: primary ovarian mass, omental ‘‘cake’’, and peritoneal deposits. Dynamic contrast‐enhanced MRI was performed using a three‐dimensional T₁‐weighted gradient‐echo acquisition with a temporal resolution of 1.6 sec, following intravenous administration of 0.1 mmol/kg gadobutrol. Precontrast T₁ mapping, using an inversion‐recovery fast gradient‐echo sequence, was also performed. Imaging was completed in 18/19 patients, although two were subsequently excluded based on pathology results. Pharmacokinetic modeling of the data was performed according to the extended Kety model, using an arterial input function formed by concatenation of the Fritz‐Hansen and Weinmann curves. No statistically significant differences were found between the results for the three marker lesions. In the future, this work will allow kinetic modeling results from ovarian dynamic contrast‐enhanced MRI to be correlated with response to treatment. The high temporal resolution allows good characterization of the rapid contrast agent uptake in these vascular tumors. Magn Reson Med 63:1044–1049, 2010. © 2010 Wiley‐Liss, Inc.     

Absolute blood contrast concentration and blood signal saturation on myocardial perfusion MRI: Estimation from CT data

Purpose

To determine the optimal contrast injection rate and absolute blood gadolinium concentration for optimal first‐pass imaging.

Materials and Methods

The concentration of contrast medium in left ventricle (LV) was estimated from dynamic computed tomography (CT) by administering iodinated contrast medium of volume (0.2 mL/kg) equivalent to 0.1 mmol/kg of gadolinium injection in 50 subjects. A blood sample study was performed to determine the relationship between blood signal and gadolinium concentration on perfusion MRI.

Results

The mean peak gadolinium concentration in LV increased as the injection rate increased from 1 mL/sec (3.7 ± 1.2 mM), to 4 mL/sec (6.9 ± 2.7 mM) (P < 0.01). However, no significant improvement was found with an increase in the injection rate from 4 mL/sec to 5 mL/sec (6.8 ± 1.5 mM, P = 0.86). In a blood sample study the linear relationship between blood signal and gadolinium concentration was maintained in the range of ≤0.67 mM (r = 0.992), which corresponds to a peak blood concentration following a 0.01 mmol/kg gadolinium injection.

Conclusion

The optimal contrast injection rate for myocardial perfusion magnetic resonance imaging (MRI) appears to be 4 mL/sec. Saturation of arterial input signal is inevitable if the dose of gadolinium contrast medium exceeds 0.01 mmol/kg. These findings are essential for accurate quantification of myocardial blood flow from perfusion MRI. J. Magn. Reson. Imaging 2009;29:205–210. © 2008 Wiley‐Liss, Inc.     

Optimization of RF excitation to maximize signal and T2 contrast of tissues with rapid transverse relaxation

Ultrashort echo time MRI requires specialized pulse sequences to overcome the short T₂ of the MR signal encountered in tissues such as ligaments, tendon, or cortical bone. Theoretical work is presented, supported by simulations and experimental data on optimizing the radiofrequency excitation to maximize signal‐to‐noise ratio and contrast‐to‐noise ratio. The theoretical calculations and simulations are based on the classic Bloch equations and lead to a closed form expression for the optimal radiofrequency pulse parameters to maximize the MR signal in the presence of rapid T₂ decay. In the steady state, the spoiled gradient recalled echo signal amplitude in response to the radiofrequency excitation pulses is not maximized by the classic Ernst angle but by a more general criterion we call “generalized Ernst angle.” Finally, it is shown that T₂ contrast is maximized by flipping the magnetization at the Ernst angle with a radiofrequency pulse duration proportional to the targeted T₂. Experimental studies on short T₂ phantoms confirm these optimization criteria for both signal‐to‐noise ratio and contrast‐to‐noise ratio. Magn Reson Med, 2010. © 2010 Wiley‐Liss, Inc.