Gadolinium as a CT contrast agent: assessment in a porcine model

Aortoiliac Gadolinium-enhanced CT Angiography: Improved Results with a 16–Detector Row Scanner Compared with a Four–Detector Row Scanner

PURPOSE

To assess the level of vascular enhancement of gadolinium-enhanced aortoiliac computed tomographic (CT) angiography with a 16-detector row CT scanner and to compare it with the results of previous similar studies that used four-detector row CT units.

MATERIALS AND METHODS

Eleven gadolinium-enhanced CT angiograms were obtained in 10 consecutive patients with contraindication to iodinated contrast medium with use of a 16-detector row CT scanner. In the region of interest, attenuation measurements (in HU) were obtained from the proximal abdominal aorta to the common femoral arteries during unenhanced, gadolinium-enhanced, and delayed acquisitions. The results were compared to those in the 15 consecutive patients who most recently had similar examinations performed on a four-detector row CT unit. Phantom studies with diluted gadolinium were conducted to compare attenuation between CT units.

RESULTS

On four-detector row CT, throughout the scan length, mean enhancement values were 53.8 HU +/- 5.3 and 15.0 HU +/- 2.6 for gadolinium-enhanced and delayed series, respectively. For the 16-detector row CT unit, they were 76.1 HU +/- 3.4 and 21.3 HU +/- 1.3, respectively. As a result of a shorter scan time and a more optimal start time, the 16-detector row CT unit provided significantly greater and more consistent enhancement throughout the scan length compared with the four-detector row CT unit (P =.0106). Similar structures had significantly greater enhancement when 120 kV was applied instead of 140 kV (P =.0495)

CONCLUSION

The 16-detector row CT scanner improved gadolinium-enhanced CT angiography results compared with the four-detector row CT unit.

In Vivo Measurement of Gadolinium Concentration in a Rat Glioma Model by Monochromatic Quantitative Computed Tomography

RATIONALE AND OBJECTIVES

Monochromatic quantitative computed tomography allows a nondestructive and quantitative measurement of gadolinium (Gd) concentration. This technique was used in the C6 rat glioma model to compare gadopentetate dimeglumine and gadobutrol.

METHODS

Rats bearing late-stage gliomas received 2.5 mmol/kg (392.5 mg Gd/kg) of gadopentetate dimeglumine (n = 5) and gadobutrol (n = 6) intravenously before the imaging session performed at the European Synchrotron Radiation Facility.

RESULTS

Monochromatic quantitative computed tomography enabled in vivo follow-up of Gd concentration as a function of time in specified regions of interest. Surprisingly, after gadobutrol injection, Gd concentrations in the center and periphery of the tumor were higher than those after gadopentetate injection, although identical in normal and contralateral area of the brain.

CONCLUSION

The in vivo assessment of absolute Gd concentrations revealed differences in gadobutrol and gadopentetate dimeglumine behaviors in tumoral tissues despite injections in the same conditions. These differences might be attributed to different characteristics of the contrast agents.

Gadolinium-enhanced computed tomography angiography in multi-detector row computed tomography

RATIONALE AND OBJECTIVES

The feasibility of using gadolinium contrast medium for computed tomography angiography (CTA) in multi-detector row computed tomography and the effect of contrast medium dilution was investigated.

MATERIALS AND METHODS

Three pigs were each scanned in multiple sessions with injections of non-dilute and dilute contrast medium at a dose of 0.3 mmol/kg body weight. Non-spiral dynamic scanning at a fixed mid-abdominal aortic level and thoracoabdominal CTA were performed.

RESULTS

The magnitude of peak aortic enhancement was not significantly different between dilute and non-dilute contrast medium injections (P = .88), but the former showed earlier enhancement (mean of 2.3 seconds sooner, P < .01) than the latter. CT angiography with gadolinium contrast medium showed much lower enhancement than iodine contrast medium, but small vessels were readily identifiable.

CONCLUSION

Gadolinium contrast medium combined with multi-detector row computed tomography may provide clinically useful CTA. Dilution of contrast medium shortens the enhancement time but has little effect on the magnitude.

1-molar gadobutrol as a contrast agent for computed tomography: results from a comparative porcine study

RATIONALE AND OBJECTIVES

To evaluate prospectively the efficacy of gadobutrol as contrast agent for computed tomography (CT) compared with iodinated contrast media in a porcine animal model.

METHODS

In 8 domestic pigs (35 +/- 4 kg body weight [BW]), continuous spiral CTs of the chest and abdomen were performed using either 2 mmol/kg BW Gadovist 1.0 (1 mol/L gadobutrol) intravenously or Ultravist (300 mg I/mL iopromide) (slice 5 mm, table feed 7.5 mm, reconstruction increment 5 mm). One week later, the same animals were examined using the same protocol with the other contrast agent. In 2 additional animals, serial CTs were performed at the same level using gadobutrol or iopromide on day 1 and the alternate agent on day 8 inches order to determine contrast media kinetics, peak enhancement, and time enhancement-product in important vascular regions and parenchymal organs (abdominal aorta, inferior vena cava, liver, and renal parenchyma). Peak enhancement (net increase compared with nonenhanced baseline values) was measured in Hounsfield units (HU) in defined regions of interest.

RESULTS

In vivo, the mean peak enhancement 5, 15, 30, and 120 seconds in the abdominal aorta after injection of 2 mL/kg BW gadobutrol and iopromide was 200 +/- 11, 224 +/- 10, 261 +/- 13, and 95 +/- 9 HU versus 232 +/- 10, 298 +/- 10, 152 +/- 11, and 123 +/- 10 HU, respectively. Differences in enhancement of vascular structures was statistically significant (P < 0.05) in carotid arteries (235 +/- 20 HU for gadobutrol and 264 +/- 19 HU for iopromide) and the aortic arch (261 +/- 14 HU for gadobutrol and 279 HU +/- 13 HU for iopromide). No statistical significance was seen in all other measured vascular structures and parenchymal organs.

CONCLUSION

Contrast-enhanced CT with 1 mol/L gadobutrol in a dose of 2 mmol/kg BW resulted in an excellent vascular and parenchymal enhancement in most vascular regions and parenchymal organs similar to an equivalent volume of 300 mg/mL iodinated contrast media.

Gadolinium-enhanced multidetector CT angiography of the thoracoabdominal aorta

A 93-year-old patient with a cardiac pacemaker and biochemical renal failure presented with back pain suspicious for dissection. We performed gadolinium-enhanced thoracoabdominal multidetector CT angiography using eight-channel multidetector CT. Uniform aortic enhancement of 140 HU was sufficient to exclude aortic dissection and defined an unruptured infrarenal abdominal aortic aneurysm.

Gadopentetate dimeglumine is potentially an alternative contrast agent for three-dimensional computed tomography angiography with multidetector-row helical scanning

OBJECTIVE

To demonstrate that gadopentetate dimeglumine is potentially an alternative contrast medium for computed tomographic angiography (CTA).

METHODS

One 12.2-kg Beagle dog was studied as proof of principle; the cervical vessels of three adult human patients were imaged for presurgical planning of the neck. Gadopentetate dimeglumine, 0.5 mol/l (Berlex Laboratories, Wayne, NJ, U.S.A.), a LightSpeed QX/i CT (General Electric Medical Systems, Milwaukee, WI, U.S.A.), and an Ultra Sparc II (SUN Microsystems, Santa Clara, CA, U.S.A.) running Advantage Windows 3.1 (General Electric Medical Systems) were used.

RESULTS

Sufficient enhancement for CTA of the thoracic aorta, cervical vessels, and abdominal vessels was produced in the experimental dog, and the cervical vessels were clearly defined in all three patients.

CONCLUSION

In that subset of patients with contraindications to iodinated contrast medium and for whom magnetic resonance angiography is inappropriate, gadopentetate dimeglumine may be an alternative contrast medium for CTA.

Performance of computed tomography for contrast agent concentration measurements with monochromatic x-ray beams: comparison of K-edge versus temporal subtraction

We investigated the performance of monochromatic computed tomography for the quantification of contrast agent concentrations. Two subtraction methods (K-edge subtraction and temporal subtraction) were evaluated and compared theoretically and experimentally in terms of detection limit, precision and accuracy. Measurements were performed using synchrotron x-rays with Lucite phantoms (10 cm and 17.5 cm in diameter) containing iodine or gadolinium solutions ranging from 50 microg ml(-1) to 5 mg ml(-1). The experiments were carried out using monochromators developed at the European Synchrotron Radiation Facility (ESRF) medical beamline. The phantoms were imaged either above and below the contrast agent K-edge, or before and after the addition of the contrast agent. Both methods gave comparable performance for phantoms less than 10 cm in diameter. For large phantoms, equivalent to a human head, the temporal subtraction is more suitable for detecting elements such as iodine, keeping a reasonable x-ray dose delivered to the phantom. A good agreement was obtained between analytical calculations, simulations and measurements. The beam harmonic content was taken into account in the simulations. It explains the performance degradation with high contrast agent concentrations. The temporal subtraction technique has the advantage of energy tunability and is well suited for imaging elements, such as iodine or gadolinium, in highly absorbing samples. For technical reasons, the K-edge method is preferable when the imaged organ is moving since the two measurements can be performed simultaneously, which is mandatory for obtaining a good subtraction.

X-ray digital subtraction angiography with 1 mol/L gadobutrol: results from a comparative porcine study With iodinated contrast agents

RATIONALE AND OBJECTIVES

To evaluate prospectively diagnostic accuracy of 1 mol/L gadobutrol as a contrast agent for intraarterial x-ray digital subtraction angiography (DSA) in comparison to iodinated, nonionic contrast media and 0.5 mol/L gadolinium-DTPA.

METHODS

Flush arteriograms (ascending, descending, abdominal aorta, iliac, and femoral arteries) and selective angiograms (carotid, renal, and visceral arteries) were obtained from bilateral femoral arterial access (5 F sheaths) in 10 domestic pigs (70 kg body weight). Digital subtracted angiograms were obtained during injection of undiluted 1 mol/L gadobutrol, 300 mg I/mL iopromide, or 0.5 mol/L gadopentetate. Injection parameters (volume and velocity) were similar for all three contrast agents. In paired arteries, two different contrast media were used during the same angiographic run. Diagnostic quality and accuracy of the angiograms were evaluated on a three-step scale by three independent blinded investigators.

RESULTS

Sufficient nonselective angiographic images were obtained in 90% of cases using iodinated contrast material. Gadobutrol achieved sufficient nonselective angiograms in 64%. Selective angiograms were sufficient in 98% using iodinated contrast material, 90% using 1 mol/L Gadobutrol and 48% using 0.5 mol/L Gd-DTPA. Adverse reactions to any of the used contrast agents were not noted.

CONCLUSION

One mol/L Gadobutrol solution allows x-ray digital subtraction angiography with a diagnostic accuracy equivalent to 300 mg/mL iodinated contrast media, if selective injections are performed. Flush aortograms are of inferior image quality to iodinated contrast material.

Are gadolinium-based contrast media really safer than iodinated media for digital subtraction angiography in patients with azotemia?

Gadolinium chelates, intended as intravenous contrast media for magnetic resonance imaging, have been regarded as nonnephrotoxic and recommended to replace iodinated contrast media in patients with azotemia who are undergoing digital subtraction angiography (DSA). High intraarterial doses (up to 220 mmol of gadodiamide) have been used, with a 40% incidence of nephropathy. The authors discourage the use of gadolinium for DSA for several reasons. (a) There exist no randomized studies comparing the nephrotoxic effects of gadolinium-based and iodinated media at equal-attenuating concentrations and doses. (b) Gadolinium-based media are hypertonic, a pathogenetic factor in contrast medium-induced nephropathy after renal angiography, with an osmolality two to seven times that of plasma. Iodinated media in concentrations that are equally attenuating with gadolinium-based media can be made isotonic. (c) In vitro measurements indicate that 0.5 mol/L gadolinium chelates are equally attenuating with 60-80 mg iodine per milliliter at the commonly used 70-90-kV range used for DSA. Thus, 50 mL of 0.5 mol/L gadolinium chelate ( approximately 0.3 mmol/kg in an 80-kg person) would be equally attenuating with a dose of 3-4 g of iodine in an iodinated medium (eg, 50 mL iohexol at 60-80 mg I/mL or 10-13 mL at 300 mg I/mL). (d) By combining these data on attenuation and results of toxicity studies in mice, the general toxicity of gadolinium chelates may be six to 25 times higher than that of equal-attenuating doses of iodinated media at 70-kV DSA. Thus, the authors believe that at equal-attenuating doses for DSA, modern iodinated contrast media should result in a lower toxic load on the body than with presently available gadolinium chelates.

Percutaneous gadolinium injection under MR guidance to mark target for CT-guided radiofrequency ablation

Selection of the appropriate imaging tool depends on a number of factors that reflect the patient, the procedure, and the physician. Multiple imaging techniques are often required to perform elements of a whole procedure. A patient with an allergy to iodinated contrast material and a 3.0-cm hepatic metastasis that was invisible on computed tomography (CT) was treated with CT-guided radiofrequency ablation by first injecting gadolinium under magnetic resonance guidance to mark the location of the lesion. Gadolinium's high atomic number makes it a viable contrast agent for attenuating x rays under fluoroscopic or CT guidance.

Gadolinium-enhanced computed tomographic aortography

Radiographic contrast agents using gadolinium have a better safety profile and photoelectric effect than iodinated contrast, allowing use where iodinated contrast is contraindicated. A case of gadolinium-enhanced computed tomographic aortography (CTA) for suspected thoracic dissection is reported. Aortic enhancement was sufficient for confident exclusion of an intimal flap. The findings were later confirmed by MRI. Vascular enhancement diminished below the diaphragm and tissue enhancement was minimal. Gadolinium diethylenetriamine penta-acetic acid (Gd-DTPA) may be used for CTA of the thoracic aorta, where the use of iodinated contrast is contraindicated. Multi-slice CT may expand the role of gadolinium enhancement in the future.

Gadolinium-DTPA as X-ray contrast medium in clinical studies

The aim of this study was to investigate the contrast effects of gadolinium (Gd) in patients undergoing digital subtraction angiography (DSA), intravenous urography (IVU) and CT. 15 patients attending for coeliac axis DSA (n = 5), abdominal CT (n = 5) and IVU (n = 5) were injected with 0.3 mmol kg-1 Gd-DTPA, the maximum approved dose. For DSA and IVU, images were categorized as being of diagnostic or non-diagnostic quality. For CT, enhancement was measured in Hounsfield Units (HU). On CT, enhancement with Gd was reproducible in all cases; average peak aortic enhancement was 75 HU but duration was short. On IVU, four of five studies yielded positive pyelograms but all nephrograms were relatively poor. On DSA, all five patients had diagnostic arteriograms and four of five indirect portograms were of diagnostic quality. In all 15 cases, enhancement was weaker than that achieved with routine dosage of iodinated agents. In conclusion, Gd chelates may be clinically useful in X-ray studies under certain circumstances on patients with contraindications to iodinated agents. Higher doses than currently approved would be potentially useful.