High-resolution T2-weighted abdominal magnetic resonance imaging using respiratory triggering: impact of butylscopolamine on image quality

BACKGROUND

Respiratory triggering allows the acquisition of high-resolution magnetic resonance (MR) images of the upper abdomen. However, the depiction of organs close to the gastrointestinal tract can be considerably impaired by ghosting artifacts and blurring caused by bowel peristalsis.

PURPOSE

To evaluate the effect of gastrointestinal motion suppression by intramuscular butylscopolamine administration on the image quality of a respiratory-triggered T2-weighted turbo spin-echo (T2w TSE) sequence of the upper abdomen.

MATERIAL AND METHODS

Images of 46 patients were retrospectively analyzed. Twenty-four patients had received intramuscular injection of 40 mg butylscopolamine immediately before MR imaging. Fourteen of the 24 patients in the butylscopolamine group underwent repeat imaging after a mean of 29 min. Quantitative analysis of the ghosting artifacts was done by measuring signal intensities in regions of interest placed in air anterior to the patient. In addition, image quality was assessed qualitatively by two radiologists by consensus.

RESULTS

Spasmolytic medication with butylscopolamine reduced ghosting artifacts and significantly improved image quality of the respiratory-triggered T2w TSE sequence. The most pronounced effect of butylscopolamine administration on image quality was found for the pancreas and the left hepatic lobe. The rate of examinations with excellent or good depiction of the pancreas and the left hepatic lobe in the group without premedication and in the butylscopolamine group was 55% vs. 96% (pancreatic head), 35% vs. 88% (pancreatic body), 43% vs. 96% (pancreatic tail), and 45% vs. 83% (left hepatic lobe), respectively. Regarding the duration of the effect of intramuscular butylscopolamine, repeat imaging after a mean of 29 min did not result in a significant deterioration of image quality.

CONCLUSION

Intramuscular butylscopolamine administration significantly improves image quality of respiratory-triggered T2-weighted abdominal MR imaging by persistent reduction of peristaltic artifacts. MR imaging of the liver and pancreas in particular benefits from the suppression of gastrointestinal peristalsis by butylscopolamine.

Linking proteins with anionic nanoparticles via protamine: ultrasmall protein-coupled probes for magnetic resonance imaging of apoptosis

Magnetic resonance imaging (MRI) of a target in vivo depends on the surface, size, and particle relaxivity of the target-specific nanoparticles for MRI. Here a new method for decorating very small iron oxide particles (VSOPs) with target-specific ligands is described. The method is based on the electrostatic attraction of the strongly positively charged peptide protamine to the anionic citrate shell of the electrostatically stabilized VSOPs. The protamine coat allows linkage chemistry and chimera technology to functionalize VSOPs or other negative charged surfaces with biologics. Annexin A5 (anxA5)-VSOP utilizing thiol chemistry was generated to couple biologically active anxA5 to VSOPs for in vivo MRI of apoptosis. Annexin A5-VSOP comprises five anxA5 molecules per iron oxide nanoparticle with a high R2 particle relaxivity of 180 000 mM(-1) s(-1) yet small hydrodynamic diameter of only 14.7+/-2.9 nm beneficial for in vivo MRI of extravascular targets.

[Preoperative imaging in 78 living kidney donors using CE-MRA and DSA]

PURPOSE

To evaluate contrast-enhanced 3D magnetic resonance angiography (CE-MRA) and digital subtraction angiography (DSA) in comparison with the intraoperative findings in living kidney donors.

MATERIALS AND METHODS

A total of 156 kidneys in 78 potential kidney donors were prospectively examined using CE-MRA (0.2 mmol Gd/kg, voxel size 1.3 x 0.8 x 2.0) and DSA. Two experienced radiologists assessed the images in consensus regarding the renal vascular anatomy and variants. The results for the 67 candidates accepted for donation were compared to the intraoperative findings. In the other kidneys not accepted for donor nephrectomy, MRA and DSA were compared with each other.

RESULTS

Nineteen arterial variants were identified intraoperatively, of which 11 (58%) were also detected by preoperative CE-MRA and 10 (53%) by preoperative DSA. Of the 10 venous variants found intraoperatively, CE-MRA detected 8 (80%) and DSA 3 (30%). The agreement (kappa test) between MRI and DSA for all 156 evaluated kidneys was 0.7 for arterial variants (McNemar p=0.12) and 0.3 for venous variants (McNemar p=0.01). The preoperative choice of kidney (right or left) made on the basis of the renal vascular anatomy seen on CE-MRA and DSA differed in 22% of the 78 potential donors (McNemar p=0.3).

CONCLUSION

Our results in a large group of potential living kidney donors suggest that CE-MRA and DSA are comparable for detecting arterial renal variants while CE-MRA is superior for identifying venous variants. The preoperative choice of transplant kidney was not significantly influenced by the different results of CE-MRA and DSA.

Whole-heart coronary magnetic resonance angiography: contrast-enhanced high-resolution, time-resolved 3D imaging

OBJECTIVES

To test the feasibility and performance of a 4D magnetic resonance coronary angiography sequence compared with conventional inversion recovery (IR) prepared gradient echo imaging.

MATERIALS AND METHODS

A 4D sequence with 100 milliseconds temporal resolution was implemented on a 1.5 T system. Five minipigs were examined after administration of very small superparamagnetic iron oxide particles. Coronary angiographies with an isotropic resolution of 0.82 mm were performed in the pigs using 4D and IR sequences.

RESULTS

The 4D sequence allowed visualization of the coronary arteries, the effect of their movement and that of the entire heart without prolonging scan time. The contrast-to-noise ratio of the IR images was on average 38% higher than that of the corresponding 4D phase.

CONCLUSIONS

4D magnetic resonance imaging is superior in that no trigger delay time needs to be determined and an additional whole-heart cine study can be obtained.

Magnetic resonance imaging findings of atypical focal nodular hyperplasia of the liver

Atypical focal nodular hyperplasia (FNH) of the liver is a diagnostic challenge as a variety of atypical imaging findings can occur in this entity. There is no potential for malignant transformation, making noninvasive diagnosis welcome in order to avoid invasive steps such as biopsy or surgery. The present pictorial review focuses on the atypical presentation of FNH and comments on different types of contrast media available for magnetic resonance imaging of the liver.

First-Pass Whole-Body Magnetic Resonance Angiography (MRA) Using the Blood-Pool Contrast Medium Gadofosveset Trisodium

OBJECTIVES

To evaluate gadofosveset trisodium for first-pass magnetic resonance angiography (MRA) in the setting of whole-body MRA (WB-MRA).

MATERIALS AND METHODS

Forty patients were examined using either 10 mL gadofosveset trisodium (n = 20) or 30 mL gadopentetate dimeglumine (n = 20), followed by arterial-phase imaging of 4 consecutive anatomic regions. Signal intensity was measured in 2 vessels per region. Relative contrast values (RC) were calculated. Arterial contrast, venous overlay, and image quality were rated by 2 radiologists. The Mann-Whitney U test was used to test for significance.

RESULTS

Compared with gadopentetate dimeglumine, gadofosveset trisodium enhanced imaging revealed higher RC values in 2 vessel regions, with the differences being significant in 3 of 4 vessel segments. Gadofosveset trisodium revealed lower RC values in 2 regions with significant differences in 2 segments. Qualitative evaluation revealed higher ratings for gadofosveset trisodium regarding all 3 criteria with significant differences in 2 regions.

CONCLUSIONS

Gadofosveset trisodium serves well for first-pass imaging in WB-MRA.

3D and 2D delayed-enhancement magnetic resonance imaging for detection of myocardial infarction: preclinical and clinical results

RATIONALE AND OBJECTIVES

The purpose was to verify whether myocardial viability can be detected by a delayed enhancement magnetic resonance imaging (MRI) approach using a rapid three-dimensional inversion-recovery fast low-angle shot (3D IR-FLASH) sequence in a preclinical and clinical setting.

MATERIALS AND METHODS

Nonreperfused myocardial infarctions were induced in eight minipigs. Both the pigs and 15 patients with suspected myocardial infarction underwent MRI using a rapid 3D IR-FLASH sequence and a two-dimensional IR-FLASH sequence as the reference standard.

RESULTS

In the pigs, a total of 52 segments with myocardial infarction were identified with both sequences and there was good agreement in transmurality of 99.5%. The infarction volume determined with the 3D IR-FLASH in the animal study (2.4 +/- 1.5 cm(3)) showed a good correlation with the histomorphometrically determined volume using triphenyltetrazolium chloride (2.3 +/- 1.2 cm(3), r = 0.98, P < .001) and the two-dimensional IR-FLASH sequence (2.3 +/- 1.4 cm(3), r = 0.99, P < .001). Eleven of 15 patients were found to have myocardial infarction in 37 myocardial segments with both sequences and there was a good agreement in transmurality of 98.8%. There was also a good correlation in the clinical study between the 3D and 2D sequences (6.9 +/- 6.7 cm(3) vs. 6.8 +/- 6.5 cm(3), r = 0.98, P < .001). In Bland-Altman analysis there was no significant under- or overestimation of the myocardial infarction volume using the 3D IR-FLASH sequence in comparison to the two-dimensional reference standard in both the preclinical and clinical study. The contrast-to-noise ratios were not significantly different between 3D and 2D sequences in the animal (34.7 +/- 1.5 vs. 33.8 +/- 2.6; P = .51) and clinical study (31.4 +/- 12.5 vs. 36.7 +/- 11.5; P = .31). The breathhold time for the 3D IR-FLASH sequence in the clinical study (20.4 +/- 2.2 s) was significantly shorter than that of the 2D IR-FLASH sequence (190.1 +/- 20.8 s, P < .001).

CONCLUSIONS

The rapid 3D IR-FLASH sequence detects myocardial infarction with high accuracy and allows a relevant reduction in acquisition time.

Mouse model mimics multiple sclerosis in the clinico-radiological paradox

The value of experimental autoimmune encephalomyelitis (EAE), an animal model of multiple sclerosis, in deriving novel diagnostic and therapeutic input has been subject to recent debate. This study is the first to report a disseminated distribution of plaques including cranial nerves, prior to or at early stages of disease in murine adoptive transfer EAE, irrespective of the development of clinical symptoms. We induced EAE by adoptive proteolipid protein-specific T-cell transfer in 26 female SJL/J mice, and applied high-field-strength magnetic resonance imaging (MRI) scans longitudinally, assessing blood-brain barrier (BBB) disruption by gadopentate dimeglumine enhancement. We visualized inflammatory nerve injury by gadofluorine M accumulation, and phagocytic cells in inflamed tissue by very small anionic iron oxide particles (VSOP-C184). MRI was correlated with immunohistological sections. In this study, we discovered very early BBB breakdown of white and grey brain matter in 25 mice; one mouse developed exclusively spinal cord inflammation. Widely disseminated contrast-enhancing lesions preceded the onset of disease in 10 animals. Such lesions were present despite the absence of any clinical disease formation in four mice, and coincided with the first detectable symptoms in others. Cranial nerves, predominantly the optic and trigeminal nerves, showed signal intensity changes in nuclei and fascicles of 14 mice. At all sites of MRI lesions we detected cellular infiltrates on corresponding histological sections. The discrepancy between the disease burden visualized by MRI and the extent of disability indeed mimics the human clinico-radiological paradox. MRI should therefore be implemented into evaluational in vivo routines of future therapeutic EAE studies.

Improved Evaluation of Myocardial Perfusion and Viability With the Magnetic Resonance Blood Pool Contrast Agent P792 in a Nonreperfused Porcine Infarction Model

OBJECTIVES

To investigate whether a magnetic resonance (MR) blood pool contrast agent enables both evaluation of myocardial perfusion and viability in nonreperfused infarction in pigs.

MATERIALS AND METHODS

An optimized MR protocol using the blood pool contrast agent P792 (0.026 mmol/kg, twice the clinical dose, Guerbet, France) was investigated to evaluate nonreperfused myocardial infarction in an animal model. P792 was compared with the extracellular contrast agent Gd-DOTA (0.1 mmol/kg). The MRI findings were compared with histomorphometry performed with microspheres to evaluate perfusion and triphenyltetrazolium chloride (TTC) to evaluate viability. Contrast-enhanced MR imaging of the heart was performed on a 1.5-Tesla scanner 2 days after instrumentation in 6 minipigs. A saturation recovery steady-state free precession sequence was used for perfusion imaging and an inversion recovery fast low-angle shot sequence for evaluation of myocardial viability.

RESULTS

P792 tended to depict areas of reduced perfusion more accurately than Gd-DOTA (17.2% +/- 11.1% versus 13.7% +/- 8.0%) in comparison to the gold standard of histomorphometry with microspheres (18.2% +/- 9.8%). Moreover, P792, but not Gd-DOTA, depicted ischemic areas for 30 minutes after intravenous injection. The change in myocardial signal intensity during first pass was not significantly different after P792 compared with Gd-DOTA (140.3% +/- 64.4% versus 123.3% +/- 22.5%, P = 0.56). P792 was highly accurate in depicting infarcted areas (11.1% +/- 7.1%) compared with Gd-DOTA (12.1% +/- 8.2%, r = 0.98, P < 0.001) and histomorphometry with TTC (12.2% +/- 8.0%, r = 0.99, P < 0.001).

CONCLUSIONS

Unlike Gd-DOTA, the blood pool contrast agent P792 allows evaluation of myocardial perfusion for a period of 30 minutes and shows good agreement with histomorphometry. P792 must be examined in further studies to evaluate its potential in evaluating early myocardial lesions and reperfusion. In addition, P792 also allows for evaluation of myocardial viability.

Gadobenate dimeglumine-enhanced MR angiography: Diagnostic performance of four doses for detection and grading of carotid, renal, and aorto-iliac stenoses compared to digital subtraction angiography

PURPOSE

To determine the diagnostic performance of contrast-enhanced MR angiography (CE-MRA) with four doses of gadobenate dimeglumine for detection of significant steno-occlusive disease of the carotid, renal, and pelvic vasculature.

MATERIALS AND METHODS

Eighty-four patients with suspected disease of the renal (n = 16), pelvic (n = 41), or carotid (n = 27) arteries underwent CE-MRA (3D-spoiled gradient-echo sequences) at 1.5T. CE-MRA was performed with gadobenate dimeglumine at 0.025, 0.05, 0.1, or 0.2 mmol/kg (23, 24, 19, and 18 patients, respectively) administered at 2 mL/sec. Accuracy, sensitivity, specificity, and positive and negative predictive values (PPV and NPV, respectively) for detection of significant disease (>50% stenosis or occlusion for renal/pelvic arteries; >70% stenosis or occlusion for carotid arteries) was determined by three fully blinded, independent radiologists using conventional digital subtraction angiography (DSA) as reference standard. All comparisons were tested statistically (ANOVA, chi-square, and Mantel-Haenszel tests as appropriate) and reader agreement (kappa) was assessed.

RESULTS

Values for accuracy, sensitivity, specificity, PPV, and NPV on CE-MRA were consistently higher for 0.1 mmol/kg gadobenate dimeglumine (accuracy = 95.2-97.3%, sensitivity = 84.2% (all readers), specificity = 96.9-99.2%, PPV = 80.0-94.1%, NPV = 97.6-97.7%). The greater accuracy of the 0.1 mmol/kg dose was significant (P < 0.01, all readers) compared to all other dose groups. Agreement between the three readers was good for all dose groups (kappa >/=0.58), with the highest percent agreement (85.7%) noted for the 0.1 mmol/kg dose.

CONCLUSION

Significantly better diagnostic performance on CE-MRA of the renal, pelvic, and carotid arteries is achieved with a gadobenate dimeglumine dose of 0.1 mmol/kg bodyweight.

Cine magnetic resonance imaging of the small bowel: comparison of different oral contrast media

PURPOSE

To evaluate several substances regarding small bowel distension and contrast on balanced steady-state free precession (bSSFP) cine magnetic resonance (MR) images.

MATERIAL AND METHODS

Luminal contrast was evaluated in 24 volunteers after oral application of two different contrast agent groups leading to either bright lumen (pineapple, blueberry juice) or dark lumen (tap water, orange juice) on T1-weighted images. Bowel distension was evaluated in 30 patients ingesting either methylcellulose or mannitol solution for limiting intestinal absorption. Fifteen patients with duodeno-jejunal intubation served as the control. Quantitative evaluation included measurement of luminal signal intensities and diameters of four bowel segments, qualitative evaluation assessed luminal contrast and distension on a five-point scale.

RESULTS

Quantitative and qualitative evaluation of the four contrast agents revealed no significant differences regarding luminal contrast on bSSFP images. Quantitative evaluation revealed significantly lower (P<0.05) small bowel distension for three out of four segments (qualitative evaluation: two out of four segments) for methylcellulose in comparison to the control. Mannitol was found to be equal to the control.

CONCLUSION

Oral ingestion of tap water or orange juice in combination with mannitol is recommended for cine MR imaging of the small bowel regarding luminal contrast and small bowel distension on bSSFP sequences.

Uterine Fibroids: Contrast-enhanced MR Angiography to Predict Ovarian Artery Supply—Initial Experience

PURPOSE

To prospectively evaluate the diagnostic performance of contrast material-enhanced magnetic resonance (MR) angiography in helping predict ovarian artery supply of uterine fibroids by using postembolization conventional aortography as the reference standard.

MATERIALS AND METHODS

The protocol for the study was approved by the institutional review board, and each patient gave informed consent. Ninety consecutive women (mean age, 42.5 years; range, 33-63 years) underwent MR angiography before uterine artery embolization (UAE). The number and origin of the ovarian arteries were determined. Ovarian artery supply of fibroids was graded as very unlikely, possible, or very likely by using a scoring system based on a combination of MR angiographic findings. MR angiographic results were compared with those of conventional aortography performed after UAE in all patients and followed by selective angiography in case of a suspected ovarian artery supply of fibroids. Analysis of the association between MR angiographic grading and conventional angiography as the standard of reference was performed with a chi(2) trend test. Sensitivity and specificity, including exact 95% confidence intervals (CIs), of MR angiography were determined.

RESULTS

MR angiography depicted 18 ovarian arteries (four bilateral, 10 unilateral), one with an atypical origin. Five ovarian arteries were classified as very likely; three, as possible; and 10, as very unlikely sources of arterial fibroid supply. Seven (39%) of 18 ovarian arteries detected at MR angiography were visible at conventional aortography. Fibroid supply was verified at selective angiography in five ovarian arteries in five (6%) of 90 patients. There was a strong association between MR angiographic grading and the results of conventional angiography (P = .002). Sensitivity of MR angiography in depicting ovarian artery supply (grade, possible or very likely) was 100% (five of five, 95% CI: 48%; 100%) and specificity was 77% (10 of 13, 95% CI: 46%; 95%).

CONCLUSION

Contrast-enhanced MR angiography can help predict ovarian artery supply of uterine fibroids.

Local staging of rectal cancer: the current role of MRI

With the advent of powerful gradient coil systems and high-resolution surface coils, magnetic resonance imaging (MRI) has recently extended its role in the staging of rectal cancer. MRI is superior to endorectal ultrasound, the most widely used staging modality in patients with rectal tumors, in that it visualizes not only the intestinal wall but also the surrounding pelvic anatomy. The crucial advantage of MRI is not that it enables exact T-staging but precise evaluation of the topographic relationship of a tumor to the mesorectal fascia. This fascia is the most important anatomic landmark for the feasibility of total mesorectal excision, which has evolved into the standard operative procedure for the resection of cancer located in the middle or lower third of the rectum. MRI is currently the only imaging modality that is highly accurate in predicting whether or not it is likely that a tumor-free margin can be achieved and thus provides important information for planning of an effective therapeutic strategy, especially in patients with advanced rectal cancer.

Combination of free-breathing and breathhold steady-state free precession magnetic resonance angiography for detection of coronary artery stenoses

PURPOSE

To analyze the incremental diagnostic value of a combination of two approaches (free-breathing and breathhold) vs. the sole free-breathing approach to coronary magnetic resonance angiography (CMRA) for detection of significant stenoses.

MATERIALS AND METHODS

Thirty patients were consecutively included in this prospective trial. CMRA was performed on a 1.5-T MR scanner (Magnetom Sonata, Siemens) using a balanced steady-state free precession (SSFP) sequence during free-breathing (2.4 x 0.9 x 0.7 mm3). Breathholding acquisitions (3.0 x 1.5 x 0.7 mm3) were only performed in cases in which the quality of free-breathing CMRA precluded assessment. Patients with contraindications to CMRA, claustrophobia, or nonassessable images were not excluded from the assessment of diagnostic accuracy (intention-to-diagnose design).

RESULTS

In 60% of all free-breathing coronary acquisitions the image quality was adequate for diagnostic assessment. For the remaining 40% of the cases, breathhold acquisitions were obtained. The sensitivity, specificity, nonassessable rate, and accuracy in identifying main coronary branches with significant stenoses using the combination of both breathing approaches and the free-breathing approach alone were 65% vs. 32%, 73% vs. 53%, 24% vs. 52%, and 71% vs. 46%, respectively (P < 0.001).

CONCLUSION

In this consecutive cohort of patients, the combination of free-breathing and breathhold CMRA significantly improved diagnostic accuracy. Nevertheless, even this combination did not reach accuracies sufficient for routine clinical application.

Noninvasive detection of coronary artery stenoses with multislice computed tomography or magnetic resonance imaging

BACKGROUND

Multislice computed tomography (CT) and magnetic resonance imaging (MRI) are the main candidates for noninvasive coronary angiography; however, multislice CT, unlike MRI, exposes patients to radiation and an iodinated intravenous contrast agent.

OBJECTIVE

To compare the diagnostic accuracy of multislice CT and MRI for noninvasive detection of clinically significant coronary stenoses (> or =50%).

DESIGN

Prospective intention-to-diagnose study.

SETTING

Single tertiary referral center, Berlin, Germany.

PATIENTS

129 consecutive patients with suspected coronary artery disease.

INTERVENTIONS

Multislice CT and MRI were both performed within a median of 1 day before conventional coronary angiography, which served as the reference standard.

MEASUREMENTS

Diagnostic performance of multislice CT and MRI.

RESULTS

129 patients completed the study. Altogether, 108 patients with 430 vessels could be examined with both multislice CT and MRI and were used for analysis. In the per-patient analysis, the sensitivity of multislice CT (92% [95% CI, 82% to 96%]) was significantly higher than that of MRI (74% [CI, 61% to 83%]; P = 0.013). The sensitivity for detecting clinically significant stenoses was 82% for multislice CT and 54% for MRI (P < 0.001). Specificity and negative predictive value of multislice CT and MRI in the per-vessel analysis were 90% versus 87% (P = 0.73) and 95% versus 90% (P = 0.032), respectively. The effective radiation dose used with multislice CT (mean, 12.3 mSv [SD, 1.4]) in a consecutive subgroup of 73 patients was not significantly different from that used with diagnostic cardiac catheterization (11.4 mSv [SD, 4.8]) (P = 0.169). Most patients (74%) indicated that they would prefer multislice CT for future diagnostic imaging (P < 0.001).

LIMITATIONS

This was a single-center study with 129 patients.

CONCLUSIONS

In patients referred for conventional coronary angiography, multislice CT compares favorably with MRI for noninvasive detection of coronary stenoses.

Wie sicher ist die MRT bei Patientinnen mit kontrazeptiven Implantaten?

When patients with an implanted contraceptive device undergo MRI, it must be ensured that the examination involves no risk to the patient (MR safety) and that the diagnosis is not affected by artifacts or the function of the device compromised (MR compatibility). Two basic types of intrauterine devices can be distinguished: the metal-containing/metal-free intrauterine device (IUD) and the hormone-containing implant, the fully metal-free intrauterine system (IUS), as well as the ESSURE insert made of stainless steel, which has been approved for use in Europe since February 2001. The metal-containing and metal-free IUDs and ESSURE are MRI compatible up to a magnetic field strength of 1.5 T. They do not interact in any relevant way with the external magnetic or high-frequency field and the temperature increase is within the physiologic range. The implants merely produce a local signal void with a shape that depends on their orientation relative to the magnetic field lines. At 3 T, only the metal-free IUD and the IUS are MRI safe in terms of the material used. In contrast, metal-containing IUDs and the ESSURE have not yet been fully evaluated in the 3 T field, which is why they represent a contraindication to MRI. No data are available on the MRI compatibility at 3 T for any of these devices.