Effects of iodinated contrast and field strength on gadolinium enhancement: implications for direct MR arthrography

PURPOSE: To optimize direct magnetic resonance (MR) arthrography by determining the effect of dilution of gadolinium in iodinated contrast, saline, or albumin on T1-weighted, T2-weighted, and gradient-recalled echo (GRE) images, and the effect of scanner field strength. MATERIALS AND METHODS: Gadopentetate dimeglumine was diluted into normal saline, albumin, or iodinated contrast (0.625 mmol/liter to 40 mmol/liter). Samples were scanned at 1.5T and 0.2T. Signal intensity was measured using T1-weighted spin-echo (SE), T2-weighted SE, and two- and three-dimensional GRE (20 degrees-75 degrees flip angle) sequences. Graphical analysis of signal intensity vs. gadolinium concentration was performed. RESULTS: Albumin had no effect on gadolinium contrast. Dilution of gadolinium in iodinated contrast decreased signal intensity on all sequences compared to samples of identical concentration diluted in saline at both 1.5T and 0.2T: with a 2 mmol/liter gadolinium solution at 1.5T, signal was decreased by 26.1% on T1-weighted images, 31.7% on GRE20 images, and 28.9% on GRE45 images, and the T2 value decreased by 71.1%; at 0.2T, signal was decreased by 23.5% on T1-weighted images. On all sequences, the peak signal shifted to the left (lower gadolinium concentration) when diluted in iodinated contrast. Peak signal was also seen at different gadolinium concentrations on different sequences and field strength: at 1.5T, peak in saline/iodine was 2.5/0.625 mmol/liter on T1-weighted images, and 2.5/1.25 mmol/liter on GRE20 and GRE45 sequences. At 0.2T, peak in saline/iodine was 0.625-2.5/1.25 mmol/liter on T1-weighted images, 0.625-2.5/1.25 on GRE45 images, 2.5-10.0/1.25-5.0 mmol/liter on GRE65 images, and 1.25-5.0/0.625-1.25 mmol/liter on GRE75 images. CONCLUSION: Dilution of gadolinium in iodinated contrast results in decreased signal on T1-weighted, T2-weighted, and GRE images compared to dilution in saline or albuminfor both 1.5-T and 0.2-T scanners; if gadolinium is diluted in iodinated contrast for MR arthrography, a lower concentration should be used because the peak is shifted to the left. The use of iodinated contrast should be minimized, as it may diminish enhancement and lower the sensitivity and specificity of MR arthrography. Optimal gadolinium concentration for MR arthrography is dependent on scanner field strength and a broader range of gadolinium concentration can be used to provide maximal signal at low field strength.     

SPIO与Gd-DTPA联合增强检测大鼠肝癌病灶的实验研究

目的 :观察联合使用SPIO和Gd DTPA对大鼠肝癌模型的增强特点。材料和方法 :制作 3 0只大鼠肝癌模型 ,增强前后行MR扫描 ,平扫序列包括SE、TSE、GRE的T1、T2WI序列。增强扫描分为 4组 ,其中Gd +SPIO联合增强组 10只 ,先注射Gd DTPA ,行SE、GRET1WI扫描 ,随后给予SPIO造影剂 ,扫描序列同平扫 ;SPIO +Gd联合增强组 10只 ,先注射SPIO ,行SE、GRET1WI扫描 ,12min后再给予Gd DTPA ,扫描序列同平扫 ;Gd、SPIO增强组各为 5只 ,增强扫描序列同平扫。分析各增强扫描组中病灶的增强特点。结果 :两种联合增强方法中 ,肝脏信号强度在所有扫描序列中均较平扫时下降 ,但与SPIO增强组无差异 ;病灶的SNR、CNR在SE、GRET1WI中明显高于平扫和SPIO、Gd DTPA增强法 ;在T2WI中病灶的SNR、CNR和单独使用SPIO无显著性差异。两种联合增强方法之间的SNR和CNR在每种扫描序列中没有显著性差异。结论 :SPIO和Gd DTPA联合增强方法利用了两种造影剂的优势 ,增加了肿瘤病变的对比 ,可提高发现病变的几率。     

Magnetic resonance imaging contrast enhancement of brain tumors at 3 tesla versus 1.5 tesla

RATIONALE AND OBJECTIVES: To compare the diagnostic efficacy of a standard dose of MRI contrast agent in the evaluation of primary brain tumors and metastases using a high-field 3 tesla MR unit versus a 1.5 tesla MR unit. METHODS: Sixteen patients with brain tumors were examined at both field strengths using identical axial T1-SE protocols pre- and postcontrast (0.1 mmol/kg gadolinium), and postcontrast coronal 3D GRE with magnetization preparation (MP-RAGE), which was adjusted separately for each field strength. Evaluation of the images was performed quantitatively and, in the case of T1-SE images, also by visual assessment. RESULTS: Tumor-to-brain-contrast after gadolinium administration using statistical evaluation of MP-RAGE scans was significantly higher at 3 tesla (97.5) than at 1.5 tesla (46.3). The same was true for T1-SE sequences (93.0 vs. 72.1). Signal enhancement of the lesions in T1-SE sequences was not significantly different between both field strengths. CONCLUSIONS: Administration of a gadolinium contrast agent produces higher contrast between tumor and normal brain at 3 tesla than at 1.5 tesla.     

Enhanced MRI of breast cancer smaller than 3 cm]

Twenty-two patients with breast cancers were studied using magnetic resonance (MR) imaging with a cylindrical surface coil at 1.5 Tesla. All were examined with the FE sequence and Gd-DTPA as a contrast medium. These images were compared with micrographs of the specimens. All cancers were enhanced clearly, and demarcated margins or spiculations of the tumors were seen as clearly on MR images as on micrographs of the specimens. In 12 patients (9 carcinomas, 2 fibroadenomas and 1 benign phyllodes tumor), dynamic studies were performed after the intravenous injection of Gd-DTPA. All nine carcinomas showed enhancement characterized by a sudden increase in signal intensity on the order of 100% or more within the first 2 minutes after injection. Two fibroadenomas were enhanced slowly. Thirteen patients with breast cancers were examined with several sequences (FE, T1-weighed SE, T2-weighed SE and STIR) with or without Gd-DTPA. The most clearly delineated images of the tumors were those of FE images with Gd-DTPA enhancement. A phantom constituted of various concentrations of Gd-DTPA in 20% albumin solution was measured by signal intensities with T1-weighted SE sequence and FE sequence. The ratio of enhancement of the 20% albumin solution relative to the Gd-DTPA concentration was higher with the FE sequence than with the SE sequence. The sensitivity of the FE sequence to Gd-DTPA enhancement was 1.5 times that of the SE sequence under the usual concentration of Gd-DTPA.     

MR imaging of the liver with Gd-BOPTA: quantitative analysis of T1-weighted images at two different doses.

This study evaluates the efficacy of gadobentate-dimeglumine (Gd-BOPTA) for enhancement of liver signal-to-noise ratio (SNR) and lesion-liver contrast-to-noise ratio (CNR) on T1-weighted spin-echo (SE) and gradient-recalled-echo (GRE) images at two different doses. Fifty patients with known or suspected liver lesions were examined at 1.5 T. T1-weighted SE (TR/TE 300/12 msec) and GRE images (TR/TE80/4.2 msec/flip angle 80 degrees) were obtained before and at 40-80 minutes and 90-120 minutes after administration of 0.05 or 0.1 mmol/kg Gd-BOPTA. Quantitative measurements of tissue signal intensity were performed at each dose. Liver showed significant enhancement after Gd-BOPTA on T1-weighted SE and GRE images (0.05 mmol: P < 0.05; 0.1 mmol: P < 0.001). The dose of 0.1 mmol/kg provided higher liver SNR than 0.05 mmol/kg. Mean liver SNR was higher on GRE than SE images (P < 0.0001). Lesion-liver CNR significantly increased on GRE images after 0.1 mmol (P < 0.05). There was a trend toward superiority of 0.1 mmol over 0.05 mmol/kg. GRE images were superior to SE images for pre- and post Gd-BOPTA lesion-liver CNR (P < 0.05). Our study suggests that Gd-BOPTA provides prolonged enhancement of liver SNR and CNR, that a dose of 0.1 mmol/Kg appears to be superior than 0.05 mmol/Kg, and that GRE techniques should be used in preference over SE techniques.     

Characterization of a gadolinium-labeled cholesterol derivative as an organ-specific contrast agent for adrenal MR imaging

The purpose of the study was to determine if derivatization of cholesterol with a paramagnetic label could result in an organ-specific contrast agent for magnetic resonance imaging of the adrenal glands. Gadolinium-DO3A-labeled cholesterol was synthesized and the relaxivities in water and blood plasma determined at 0.47 T and 40°C. Organ distribution was measured at 2 (n = 2) and 24 (n = 2) hours after intravenous injection of a 50 μmol/kg dose of Gd-DO3A-cholesterol in rats weighing 220–240 g. T1-weighted spin-echo images were acquired at 2 T before and after injection of 50 μmol/kg Gd-DO3A-cholesterol (n = 2) and Gd-DTPA (diethylenetriaminepentaacetic acid)-albumin (n = 2). More than 99% of the Gd-DO3A-cholesterol was found to be protein bound in bovine serum. High T1 and T2 relaxivities were found in water and plasma. High tissue concentrations of Gd-DO3A-cholesterol were found only in adrenal glands and liver. At 24 hours, adrenal gadolinium concentrations were about 10 times higher than in blood. At 2 hours after injection of Gd-DO3A-cholesterol. enhancement was 162% in adrenal glands and 146% in liver. With Gd-DTPA-albumin, enhancement values were 57% and 56%. respectively.     

Contrast-enhanced MR imaging of the liver: Comparison between Gd-BOPTA and mangafodipir

The purpose of the study was to evaluate the MR contrast agents gadolinium benzyloxypropionictetro-acetate (Gd-BOPTA) and Mangafodipir for liver enhancement and the lesion-liver contrast on T1W spin-echo (SE) and gradient-recalled-echo (GRE) images. Fifty-one patients (three groups of 17 patients each) with known or suspected liver lesions were evaluated with T1W SE (300/12) and GRE (77-80/2.3-2.5/80°) images before and after intravenous (IV) Gd-BOPTA (0.1 or 0.05 mmol/kg) or Mangafodipir (5 μmol/kg) in phase II to III clinical trials. Quantitative analysis by calculating liver signal-to-noise ratio (SNR), lesion-liver contrast-to-noise ratio (CNR), and spleen-liver CNR was performed. Liver SNR and spleen-liver CNR were always significantly increased postcontrast. SNR was highest after application of 0.1 mmol/kg Gd-BOPTA (51.3 ± 3.6, P < .05). CNR was highest after Mangafodipir (?22.6 ± 2.7), but this was not significantly different from others (P = .07). Overall, GRE images were superior to SE images for SNR and CNR. Mangafodipir and Gd-BOPTA (0.1 mmol/kg) provide equal liver enhancement and lesion conspicuity postcontrast. By all criteria, contrast-enhanced T1-weighted GRE were comparable to SE images.     

Comparison of Gd-DTPA-induced signal enhancements in rat brain C6 glioma among different pulse sequences in 3-Tesla magnetic resonance imaging

Background: T1-shortening contrast media are routinely used in magnetic resonance (MR) examinations for the diagnosis of brain tumors. Although some studies show a benefit of 3 Tesla (T) compared to 1.5T in delineation of brain tumors using contrast media, it is unclear which pulse sequences are optimal.

Purpose: To compare gadopentetate dimeglumine (Gd-DTPA)-induced signal enhancements in rat brain C6 glioma in the thalamus region among different pulse sequences in 3T MR imaging.

Material and Methods: Five rats with a surgically implanted C6 glioma in their thalamus were examined. T1-weighted brain images of the five rats were acquired before and after Gd-DTPA administration (0.1 mmol/kg) using three clinically available pulse sequences (spin echo [SE], fast SE [FSE], fast spoiled gradient echo [FSPGR]) at 3T. Signal enhancement in the glioma (E_T) was calculated as the signal intensity after Gd-DTPA administration scaled by that before administration. Pulse sequences were compared using the Tukey-Kramer test.

Results: E_T was 1.12±0.05 for FSE, 1.26±0.11 for FSPGR, and 1.20±0.11 for SE. FSPGR showed significantly higher signal enhancement than FSE and comparable enhancement to SE.

Conclusion: FSPGR is superior to FSE and comparable to SE in its ability to delineate rat brain C6 glioma in the thalamus region.     

New generation of monomer-stabilized very small superparamagnetic iron oxide particles (VSOP) as contrast medium for MR angiography: preclinical results in rats and rabbits

The purpose of this study was to evaluate the signal enhancement characteristics of very small superparamagnetic iron oxide particles (VSOP)-C63, a new monomer-coated, iron oxide-based magnetic resonance (MR) blood pool contrast medium with a very small particle size and optimized physical properties. Equilibrium MR angiography (MRA) of rats (thoracic and abdominal vessels) was performed at 1.5 T with a three-dimensional gradient-recalled echo (3D GRE) technique (TR/TE 6.6/2.3 msec, flip angle 25 degrees ) before and after (every 3-5 minutes up to 50 minutes) i.v. injection of VSOP-C63 [dosages: 15, 30, 45, 60, 75, and 90 micromol Fe/kg; diameter: 8 nm; relaxivities at 0.47 T: R1 = 30 l/(mmol * s); R2 = 39 l/(mmol * s)]. First-pass MRA images (3D-GRE, TR/TE 4.5/1.7 msec, flip angle 25 degrees ) were obtained with 45 micromol Fe/kg VSOP-C63 in comparison with 0.2 mmol Gd/kg of gadolinium diethylene triamine pentaacetic acid (Gd DTPA; before and every 5 seconds p.i.). MRA (3D GRE, TR/TE 4.5/1.7 msec, flip angle 25 degrees) of coronary vessels in rabbits was performed after i.v. injection of 45 micromol Fe/kg of VSOP-C63. In rats maximal S/N ratio in thoracic and abdominal arteries directly after i.v. injection of VSOP-C63 was 25 +/- 1, 43 +/- 2, 49 +/- 4, 57 +/- 3, 64 +/- 3, and 63 +/- 3 for the different dosages. Blood half-life was dose dependent (15 +/- 2, 20 +/- 3, 29 +/- 6, 37 +/- 5, 61 +/- 16, and 86 +/- 21 minutes). At a dose of 30 micromol Fe/kg even small intrarenal arteries were sharply delineated. First-pass MRA showed no significant difference in the S/N ratio between Gd-DTPA (71.5 +/- 11.5) and VSOP-C63 (65.1 +/- 18. 3). The proximal segments of the coronary arteries in rabbits were clearly depicted at a dose of 45 micromol Fe/kg. The monomer-coated, iron oxide-based contrast medium VSOP-C63 exhibits favorable properties as a blood pool agent for both equilibrium and first-pass MRA. J. Magn. Reson. Imaging 2000;12:905-911.     

脑肿瘤磁化传递成像和钆剂增强协同作用的研究

目的：研究钆剂（磁显葡胺）和磁化传递（ＭＴ）成像对脑肿瘤增强效果的协同作用。材料和方法：对６０例脑肿瘤行ＳＥＴ１Ｗ和ＰＤＷ，Ｔ２ＷＭＲＩ检查后，继以行钆剂增强后ＳＥＴ１Ｗ和ＭＴＩＳＥＴ１ＷＭＲＩ。然后测定各种脑肿瘤钆剂和ＭＴＩ合用的增强效价。结果：ＭＴＩ能降低脑实质（背景）信号强度，而对肿瘤病灶的信号强度无甚影响，所以钆剂和ＭＴＩ合用的增强效果为不用ＭＴＩ者的２．２４～８倍。能使脑肿瘤病灶增强范围和突出程度有所增加，并显示更多的病灶。ＭＴＩ和半量（０．０５ｍｍｏｌ／ｋｇ）钆剂合用其增强效果相当于双倍剂量钆剂者。结论：ＭＴＩ和钆剂增强对脑肿瘤具有协同增强效果，故可用作脑肿瘤增强ＭＲＩ检查的常规方法。     

The efficacy of gadobenate dimeglumine (Gd-BOPTA) at 3 Tesla in brain magnetic resonance imaging: comparison to 1.5 Tesla and a standard gadolinium chelate using a rat brain tumor model

OBJECTIVES: The objectives of this study were to analyze the differences in contrast enhancement using gadobenate dimeglumine (Gd-BOPTA or MultiHance) at 3 T versus 1.5 T and to compare Gd-BOPTA with a standard gadolinium chelate, gadopentetate dimeglumine (Gd-DTPA or Magnevist), at 3 T in a rat glioma model. MATERIALS AND METHODS: Twelve rats with surgically implanted gliomas were randomized to either comparing Gd-BOPTA at 1.5 T versus 3 T (n=7) or comparing Gd-BOPTA and Gd-DTPA at 3 T (n=5). Matched T1-weighted spin-echo techniques were used for both comparisons and the order of examinations was randomized. Signal-to-noise ratio (SNR), contrast-to-noise ratio (CNR), and lesion enhancement (LE) were evaluated using a region-of-interest analysis. A veterinary histopathologist evaluated all brain specimens. RESULTS: In the evaluation of Gd-BOPTA at 3 T and 1.5 T, there were significant increases in SNR, LE, and CNR at 3 T. Average increases in brain and tumor SNR were 93% (P<0.0001) and 92% (P<0.0001), respectively. CNR increased by 121% (P<0.0001). Comparison of Gd-BOPTA and Gd-DTPA at 3 T demonstrated significantly higher CNR and LE with Gd-BOPTA. CNR increased by 35% (P=0.002). LE increased by 44% (P=0.03). CONCLUSIONS: Gd-BOPTA provides significantly higher CNR at 3 T compared with 1.5 T and also demonstrates significantly higher CNR when compared with a standard Gd-chelate at 3 T. As a result of transient protein binding, Gd-BOPTA may be superior to standard gadolinium chelates in neurologic imaging at 3 T.     

Enhancement effects of hepatic dynamic MR imaging at 3.0 T and 1.5 T using gadoxetic acid in a phantom study: comparison with gadopentetate dimeglumine

To identify the optimum sequence at gadoxetic acid enhanced hepatic dynamic magnetic resonance imaging in the arterial phase, we studied phantoms that contained gadoxetic acid or gadopentetate dimeglumine diluted in human blood. We obtained magnetic resonance images at 3.0 T and 1.5 T with one vendor (Siemens) using 3D‐gradient echo (GRE)‐, 2D‐fast low angle shot (FLASH)‐, and turbo spin echo sequences. Contrast ratio was highest for 3D‐GRE; at both 3.0 T and 1.5 T it was superior when the contrast agent was gadoxetic acid. With both gadoxetic acid and gadopentetate dimeglumine, contrast ratio peaked at around 5‐and 2 mmol/L on 3D‐GRE‐ and 2D‐FLASH images, respectively. Compared with gadopentetate dimeglumine, at 3.0 T, the peak contrast ratio of gadoxetic acid was 14.1% better on 3D‐GRE images and 14.0% better on 2D‐FLASH images; at 1.5 T it was 16.4% better on 3D‐GRE‐ and 5.7% better on 2D‐FLASH images. With respect to the magnetic field strength, at 3.0 T the peak contrast ratio of gadoxetic acid was 6.0% better than at 1.5 T on 3D‐GRE images and 49.5% better on 2D‐FLASH images; it was 8.5% better on 3D‐GRE‐ and 44.6% better on 2D‐FLASH images than when the contrast agent was gadopentetate dimeglumine. Thus, gadoxetic acid yielded better enhancement on 3D‐GRE images acquired at 3.0 T than at 1.5 T and enhancement was better than that obtained with gadopentetate dimeglumine at the same concentration. Magn Reson Med 66:213–218, 2011. © 2011 Wiley‐Liss, Inc.     

Signal modulation in (1)H magnetic resonance spectroscopy using contrast agents: proton relaxivities of choline, creatine, and N-acetylaspartate.

The effect of gadolinium diethylenetriaminepentaacetic acid (Gd-DTPA) on the proton relaxation properties of choline, creatine and N-acetylaspartate has been assessed quantitatively. The compounds studied, either directly or indirectly as chemical constituents of other compounds, contribute to proton MR spectroscopy observable metabolite resonances. The longitudinal and transverse Gd-DTPA proton relaxivities of the methyl groups of choline, creatine, and N-acetylaspartate have been determined at 1.5 T. The longitudinal relaxivity of lactate has also been measured. Longitudinal and transverse relaxivity values were found to vary in the order N-acetylaspartate < creatine < choline. Using choline as an example, the maximum possible signal enhancement predicted in vivo in the presence of 0.5 mM Gd-DTPA (using a T(1)-weighted sequence, TR = 888 msec, TE = 20 msec) was found to be approximately 100 %. For a T(2)-weighted sequence (TR = 3000 msec, TE = 270 msec) a maximum signal loss of 53 % was calculated. The present study indicates why the use of contrast agents in spectroscopic investigations may lead to significant changes in signal intensities. Magn Reson Med 42:1155-1158, 1999.     

Radiologic diagnosis of spondylodiscitis: role of magnetic resonance

PURPOSE: To report the Magnetic Resonance Imaging (MRI) features of acute and chronic spontaneous spondylodiscitis as well as any typical patterns which can be useful for the differential diagnosis between pyogenic and tuberculous forms. MATERIAL AND METHODS: Eleven patients affected with spontaneous spondylodiscitis were selected for the study; they were 7 men and 4 women ranging in age 33-87 years (mean: 64). We excluded the patients with iatrogenic spondylodiscitis. MR images were acquired with a superconductive magnet at 1.5, with the following sequences: sagittal PD and T2-weighted TSE, sagittal T1-weighted SE, axial PD and T2-weighted TSE for the lumbar spine, axial T2-weighted GRE for the cervical and dorsal spine and axial and sagittal T1-weighted SE after contrast agent (gadolinium DTPA) injection. MR images were reviewed by three experienced radiologists and morphological and signal intensity changes of vertebral body and disk were recorded on a standard form. In 9 patients it was possible to compare MR to CT findings. RESULTS: At the time of our observation all patients reported pain at the spine level, associated with fever and weight loss in 50% of cases and with increased values of the inflammatory markers. Three patients had infectious diseases in other organs and 2 were diabetics. Biopsy was performed in two cases only and demonstrated Staphylococcus aureus in one and Mycobacterium tuberculosis in the other patient. MRI allowed the correct diagnosis to be made in all cases, demonstrating the pathological involvement of the paravertebral structures and into the spinal canal earlier and more accurately than CT. A common finding in pyogenic and tuberculous spondylodiscitis was the low signal of the subcortical bone marrow on T1-weighted sagittal images, which enhanced after Gd-DTPA administration and became intermediate or high on T2-weighted images. Moreover, the steady high signal intensity of the disk on T2-weighted images and its contrast enhancement on T1-weighted images is typical for an acute inflammatory process. CONCLUSIONS: Based on our personal experience and literature data, we believe MRI to be the most sensitive technique for the diagnosis of spondylodiscitis in the acute phase, whereas it is comparable to CT in the chronic stage of the disease. At present MRI does not allow to differentiate pyogenic from tuberculous forms.     

Conspicuity of zones of ablation after radiofrequency ablation in porcine livers: comparison of an extracellular and an SPIO contrast agent

PURPOSE: To compare conspicuity of zones of ablation on nonenhanced, gadopentetate dimeglumine-(Gd-DTPA) and ferucarbotran-(SPIO)-enhanced magnetic resonance (MR) images. MATERIALS AND METHODS: In all, 33 radiofrequency ablations (RFA) were performed in 17 healthy porcine livers at 1.5T MR imaging 1 day and 2 and 4 weeks after RFA: T2-weighted (w) ultra turbo spin echo (UTSE), proton density (PD)-w UTSE, T1-w gradient echo (GRE) pre- and 5 minutes postcontrast administration, dynamic T1-w GRE during Gd-DTPA (Magnevist) or SPIO (Resovist) administration, T2-w UTSE, and PD-w UTSE sequences 10 minutes after SPIO administration. Regions of interest (ROIs) for contrast-to-noise ratio (CNR) and signal-to-noise ratio (SNR) were drawn in consensus by two radiologists. RESULTS: PD-w SPIO-enhanced images (23.5 +/- 5.5) showed higher liver-to-lesion CNR than T1-w GRE Gd-DTPA-enhanced images (13.5 +/- 6.1) 1 day after RFA (P < or = 0.05). At all other timepoints, liver-to-lesion CNR of PD-w and T2-w SPIO-enhanced images did not differ significantly from T1-w GRE Gd-DTPA-enhanced images (P > or = 0.05). Nonenhanced T2-w images revealed lower liver-to-lesion CNR (7.0 +/- 7.5/6.5 +/- 5.9/6.8 +/- 5.0, 1 day/2 weeks/4 weeks, respectively) than T2-w SPIO-enhanced (17.4 +/- 4.8/15.3 +/- 4.5/14.2 +/- 5.7), PD-w SPIO-enhanced (23.5 +/- 5.5/16.9 +/- 3.6, 1 day/2 weeks), and T1-w Gd-DTPA-enhanced (15.3 +/- 3.6/12.7 +/- 3.5, 2/4 weeks) images (P < or = 0.05). Liver-to-lesion CNR of SPIO-enhanced dynamic T1-w GRE images after 30, 80, 150, and 240 seconds did not change significantly over time (P > or = 0.05). CONCLUSION: One day after RFA lesion conspicuity on PD-w ferucarbotran-enhanced images is better than on T1-w GRE Gd-DTPA-enhanced images. At all other timepoints, ferucarbotran is not superior to gadolinium. Ferucarbotran- and gadolinium-enhanced images improve lesion conspicuity compared with nonenhanced T2-w images at all timepoints.     

Theoretical analysis of gadopentetate dimeglumine enhancement in T1-weighted imaging of the brain: Comparison of two-dimensional spin-echo and three-dimensional gradient-echo sequences

By using a theoretical model, the signal difference-to noise ratios between simulated lesions and normal white matter and gray matter were calculated as a function of lesion concentration of gadopentetate dimeglumine (GD) for two-dimensional (2D) T1-weighted spin-echo (SE), three-dimensional (3D) steady-state spoiled gradient-echo (GRE) (FLASH [fast low-angle shot]), and 3D magnetization-prepared rapid gradient echo (MP-RAGE) pulse sequences. The 3D GRE sequences provided greater contrast enhancement at relatively high [GD], and the 2D SE sequence demonstrated greater enhancement and a higher rate of enhancement at low [GD]. The results predict that at low [GD], certain lesions could probably be detected with the 2D SE sequence but possibly not with one or both of the 3D GRE sequences. At high [GD], certain lesions could probably be detected with one or both of the 3D GRE sequences but possibly not with the 2D SE sequence. This provides a potential explanation for the clinical observation that certain contrast agent enhanced lesions appear less conspicuous on 3D GRE images than on 2D SE images and vice versa. Modified parameter values were derived for the 3D FLASH and 3D MP-RAGE sequences that are predicted to produce contrast enhancement behavior equivalent or superior to that of a conventional 2D SE sequence.     

Quantitative evaluation of the relaxivity effects of iodine on GD-DTPA enhanced MR arthrography

PURPOSE: To quantify the effect of iodine on the gadolinium (Gd) contrast-enhanced signal in MR arthrography. MATERIALS AND METHODS: Saline solutions of Gd contrast agent (0-1 mmol/liter) were mixed with iodinated contrast agent (0-185 mmol/liter). The T1 and T2 relaxation constants of these solutions were measured at 1.5T. Different types of commonly used iodinated contrast agents as well as sodium iodide (NaI) solutions were also analyzed. RESULTS: Iodine caused significant T2 shortening and some T1 shortening in Gd contrast solutions. Both contrast agents independently obeyed the standard relaxation relation, and their mixture obeyed a modified version of this relation. The side chains in various iodine molecules and their viscosities affected the relaxation properties differently. For various spin-echo (SE) sequences, the signal from synovial fluid containing different concentrations of the two contrast agents was calculated. The T2-weighted signal appeared to be most affected by the increase in iodine concentrations. In the absence of Gd contrast, all SE sequences showed an initial increase in signal from iodine contrast. CONCLUSION: A generalized relation for the relaxivities of Gd contrast in the presence of iodine was established. The side chains of iodine contrast were found to alter the relaxivities of Gd contrast. Imaging with proton density (PD)-weighted SE with only iodine contrast agent was found to be feasible.     

MR imaging of liver metastases at 1.5 T: similar contrast discrimination with T1- and T2-weighted pulse sequences

The authors evaluated soft-tissue contrast on spin-echo (SE) proton density-weighted, SE T2-weighted, SE short-echo-time (TE) T1-weighted, and gradient-echo (GRE) images of 34 patients with known hepatic tumors who underwent high-field-strength (1.5-T) magnetic resonance imaging. For solid liver tumors, the difference in the mean lesion-liver contrast-to-noise ratios (C/Ns) with T1- (GRE and SE) and T2-weighted pulse sequences was not statistically significant (P greater than .05). For nonsolid liver tumors, the T2-weighted images provided significantly greater (P less than .05) mean lesion-liver C/N than T1-weighted GRE images. Mean liver signal-to-noise ratio was significantly greater on T1-weighted GRE (P less than .0001) and T1-weighted SE (P less than .05) images than on T2- and proton density-weighted images. Qualitative analysis of T1-weighted (SE and GRE) images and proton density- plus T2-weighted images showed that lesion conspicuity was similar in 25 of 32 patients (78%). The results suggest that liver tumor imaging at high field strength can be performed with short-TE T1-weighted (SE or GRE) or conventional T2-weighted pulse sequences.     

In vivo measurements of relaxivities in the rat kidney cortex

The aim of this study was to implement a novel noninvasive method to derive the in vivo T1 relaxivity (R1) and T2 relaxivity (R2) in the rat kidney cortex. A two-compartment gadolinium diethylene triamine pentaacetic acid (Gd-DTPA) distribution model was established to estimate the bolus and infusion dosages of Gd-DTPA necessary for obtaining the required steady-state concentration levels. After a single bolus injection of (99m)Tc-DTPA, several blood samples were collected. Based on considerations from the applied two-compartment model, a steady-state concentration was predicted approximately 5-10 minutes after the bolus injection. The plasma concentration levels of Gd-DTPA were measured by simultaneous injection of (99m)Tc-DTPA. Three regions in the cortex (upper, central, and lower) of both rat kidneys were used. A statistical evaluation resulted in the following in vivo relaxivities found at 7 T: R1 = 1.04 +/- 0.08 mM(-1)s(-1) and R2 = 10.78 +/- 0.83 mM(-1)s(-1). Using a 95% confidence interval, no intracortical differences were detected. The relaxivities R1 and R2 calculated in the intact rat kidney cortex were distinctly different from relaxivities found in human plasma: (22 degrees C) 4.42 +/- 0.07 mM(-1)s(-1) (r2> 0.98) and R2 = 5.75 +/- 0.17 mM(-1)s(-1) (r2> 0.98), respectively. The measurements showed a marked difference between in vitro and in vivo relaxivities. Comparison of the distribution rates in pig, human, and rats shows a distinct proportionality between size and renal function.     

Dual contrast enhanced magnetic resonance imaging of the liver with superparamagnetic iron oxide followed by gadolinium for lesion detection and characterization

AIM: Iron oxide contrast agents are useful for lesion detection, and extracellular gadolinium chelates are advocated for lesion characterization. We undertook a study to determine if dual contrast enhanced liver imaging with sequential use of ferumoxides particles and gadolinium (Gd)-DTPA can be performed in the same imaging protocol. MATERIALS AND METHODS: Sixteen patients underwent dual contrast magnetic resonance imaging (MRI) of the liver for evaluation of known/suspected focal lesions which included, metastases (n = 5), hepatocellular carcinoma (HCC;n = 3), cholangiocharcinoma(n = 1) and focal nodular hyperplasia (FNH;n = 3). Pre- and post-iron oxide T1-weighted gradient recalled echo (GRE) and T2-weighted fast spin echo (FSE) sequences were obtained, followed by post-Gd-DTPA (0.1 mmol/kg) multi-phase dynamic T1-weighted out-of-phase GRE imaging. Images were analysed in a blinded fashion by three experts using a three-point scoring system for lesion conspicuity on pre- and post-iron oxide T1 images as well as for reader's confidence in characterizing liver lesions on post Gd-DTPA T1 images. RESULTS: No statistically significant difference in lesion conspicuity was observed on pre- and post-iron oxide T1-GRE images in this small study cohort. The presence of iron oxide did not appreciably diminish image quality of post-gadolinium sequences and did not prevent characterization of liver lesions. CONCLUSION: Our results suggest that characterization of focal liver lesion with Gd-enhanced liver MRI is still possible following iron oxide enhanced imaging.Kubaska, S.et al. (2001). Clinical Radiology, 56, 410-415 Copyright 2001 The Royal College of Radiology.