Does a higher concentration of gadolinium chelates improve first-pass cardiac signal changes?

Synthesis and characterization of new low-molecular-weight lysine-conjugated Gd-DTPA contrast agents

Various blood pool contrast agents (CAs), characterized by intravascular distribution, have been developed to assist contrast enhanced magnetic resonance angiography (MRA). Among these CAs, the DTPA derivatives conjugated to synthetic polypeptides, such as polylysine, represent attractive candidates for blood pool imaging. However, due to the presence of charged residues located on their backbone, these agents are retained in the kidneys and this compromises their long blood half-life. In order to overcome this major drawback of the polylysine compounds, two new low-molecular-weight CAs were synthesized in the present work by conjugating four or six 1-p-isothiocyanatobenzyl-DTPA moieties to tri- or penta-Lys peptides [(Gd-DTPA)(4) Lys(3) and (Gd-DTPA)(6) Lys(5)], respectively. All the -NH(2) groups of Lys were thus blocked by covalent conjugation to DTPA. The stability and relaxometric properties of these compounds, as well as their pharmacokinetic and biodistribution characteristics, were then evaluated. The half-life in blood of these new polylysine derivatives, as determined in rats, is twofold longer than that of Gd-DTPA. The compounds could thus be optimal blood pool markers for MRA, which typically uses fast acquisition times. The absence of positive molecular charge did not limit their retention in kidneys 2 h after administration. On the other hand, (Gd-DTPA)(4) Lys(3) is retained in kidneys to a lesser extent than (Gd-DTPA)(6) Lys(5) . Their moderate retention in blood and their higher stability and relaxivity in comparison with Gd-DTPA highlight these polylysine derivatives as optimal compared with previously developed polylysine compounds.

1 M Gd-chelate (gadobutrol) for multislice first-pass magnetic resonance myocardial perfusion imaging

The aim of the study was to evaluate a 1 M gadolinium-chelate (gadobutrol) for first-pass MR myocardial perfusion examinations in patients with suspected coronary artery disease (CAD). In phantom studies, signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR) values of gadobutrol were compared with gadopentetate (Gd-DTPA). 25 consecutive patients with clinically suspected CAD were examined with dynamic rest/stress MR perfusion examinations using 0.05 mmol kg(-1) gadobutrol. Semi-quantitative evaluation of the myocardial perfusion was performed by calculating the myocardial perfusion reserve index (MPRI). Hypoperfused regions were correlated with data from X-ray coronary angiography. In phantom studies, SNR/CNR of gadobutrol-doped blood samples were consistently higher for all applied flip angles at concentrations < or =1.0 mmol L(-1) compared with Gd-DTPA. Assessment of 81 stress perfusion series with gadobutrol in 25 patients yielded a sensitivity of 82% and specificity of 91% for significant CAD. Combining the information from all perfusion series of one patient yielded a sensitivity of 89% and specificity of 94% on a per-vessel basis. Gadobutrol exhibited favourable signal properties in phantom studies. Rest/stress myocardial perfusion examinations using 1 M gadobutrol yielded high sensitivity and specificity in detection of malperfused areas (82% and 91%, respectively). This is comparable with recently published perfusion data using 0.5 M Gd-DTPA.

Intraindividual comparison of 1.0 M gadobutrol and 0.5 M gadopentetate dimeglumine for time-resolved contrast-enhanced three-dimensional magnetic resonance angiography of the upper torso

PURPOSE

To compare the signal characteristics and bolus dynamics of 1.0 M gadobutrol and 0.5 M Gd-DTPA for time-resolved, three-dimensional, contrast-enhanced (CE) MRA of the upper torso.

MATERIALS AND METHODS

Ten healthy volunteers were examined with time-resolved three-dimensional CE-MRA (scan time per three-dimensional data set: 0.86 second; voxel size: 3.6 x 2 x 6.3 mm(3)). Each volunteer underwent eight individual examinations after intravenous injection of 0.05 and 0.1 mmol/kg body weight (b.w.) of 1.0 M gadobutrol and 0.5 M Gd-DTPA using two injection rates (2.5 and 5 mL/second). The data analysis included quantitative measurements of the peak signal-to-noise ratio (SNR) and bolus dispersion (full width at half maximum (FWHM)) in the pulmonary artery, left atrium, and thoracic and abdominal aortas.

RESULTS

No significant differences in the peak SNR and bolus dispersion were observed between gadobutrol and Gd-DTPA for all dose levels and injection rates in any of the vascular segments. For both contrast agents a dose of 0.1 mmol/kg b.w. injected with 5 mL/second achieved the highest SNR in all vascular segments.

CONCLUSION

For the imaging parameters used in this study, higher-concentrated gadolinium chelates offer no relevant advantages for time-resolved three-dimensional CE-MRA of the upper torso.

Contrast-enhanced blood-pool MR angiography with optimized iron oxides: effect of size and dose on vascular contrast enhancement in rabbits

PURPOSE

To investigate intravascular enhancement of bolus-injectable small and ultrasmall superparamagnetic iron oxides (USPIOs) of different particle sizes and relaxivities for first-pass and blood-pool magnetic resonance (MR) angiography.

MATERIALS AND METHODS

Iron oxides with different particle sizes (hydrodynamic diameters, 21, 33, 46, and 65 nm) were bolus injected intravenously at three doses (10, 20, and 40 micromol per kilogram body weight). An extracellular contrast agent (gadopentetate dimeglumine) served as a control. MR angiography was performed multiple times after intravenous injection (5-120 minutes and 24 hours later). Signal enhancement was calculated from signal intensity measurements in the abdominal aorta and renal and iliac arteries.

RESULTS

Highest enhancement was seen during the first pass with all contrast agents. USPIO enhancement in the abdominal aorta increased significantly with decreasing particle size (65 nm vs 33 nm, 65 nm vs 21 nm; P <.01).

CONCLUSION

The smallest iron oxide provided signal enhancement comparable with that of gadopentetate dimeglumine at 40 micromol iron per kilogram for first-pass investigations, with prolonged signal enhancement up to 25 minutes, allowing multiple measurements after injection of a single bolus.

Using highly concentrated gadobutrol as an MR contrast agent in patients also requiring hemodialysis: safety and dialysability

OBJECTIVE

The purpose of our study was to assess the safety and dialysability of gadobutrol, a new, electrically neutral, and highly concentrated MR contrast agent, in patients who require hemodialysis.

SUBJECTS AND METHODS

Eleven patients with end-stage renal failure who required ongoing hemodialysis were enrolled in our prospective study. Gadobutrol (1 mol/L) was injected IV at randomly assigned doses of either 0.1 or 0.3 mmol of gadolinium per kilogram of body weight for contrast-enhanced MR imaging. Hematology, clinical chemistry, and vital signs were closely monitored at baseline and during an observation period of 120 hr after the IV injection of gadobutrol. To calculate the dialysability, blood samples were drawn before and after each of three hemodialysis sessions. Additional arterial and venous blood sampling was performed during the first hemodialysis session after 30 and 90 min.

RESULTS

No gadobutrol-related changes in hematology, clinical chemistry, or vital signs were detected at either dose level during the observation period. The mean and the standard deviation for the eliminated fraction of gadobutrol was 68.2% +/- 12.7% after a 3-hr hemodialysis session using a 1.2 m(2) low-flux polysulfone membrane. After three consecutive hemodialysis sessions, the total amount of gadobutrol eliminated increased to 98.0% +/- 1.8%. The mean clearance rates of gadobutrol were 126.1 +/- 17.8 mL/min and 126.6 +/- 24.5 mL/min at 30 and 90 min, respectively.

CONCLUSION

Gadobutrol is effectively removed by three hemodialysis sessions using a low-flux polysulfone membrane. Our study documents initial evidence that gadobutrol can be used safely in hemodialysis patients.