[Molecular and parametric imaging with iron oxides]

Superparamagnetic iron oxide (SPIO) contrast agents, clinically established for high resolution magnetic resonance imaging of reticuloendothelial system containing anatomical structures, can additionally be exploited for the non-invasive characterization and quantification of pathology down to the molecular level. In this context, SPIOs can be applied for non-invasive cell tracking, quantification of tissue perfusion and target specific imaging, as well as for the detection of gene expression. This article provides an overview of new applications for clinically approved iron oxides as well of new, modified SPIO contrast agents for parametric and molecular imaging.

Magnetic resonance angiography follow-up examinations to detect iatrogenic pseudoaneurysms following otorhinolaryngological surgery

Endoscopic endonasal surgery on a 36-year-old man was complicated by perforation of the right internal carotid artery. The immediate, substantial haemorrhage was controlled by packing the sphenoid sinus. Intra-arterial angiography of the right internal carotid artery showed small irregularities proximal to the ophthalmic artery. A follow-up examination two weeks later documented a large pseudoaneurysm in the initially irregular arterial segment, which was successfully treated by endovascular coiling. This case report illustrates the need for angiographic follow-up examinations following traumatic intracranial vessel injury in order to identify late pseudoaneurysm development.

[The "EVA" Trial: Evaluation of the Efficacy of Diagnostic Methods (Mammography, Ultrasound, MRI) in the secondary and tertiary prevention of familial breast cancer. Preliminary results after the first half of the study period]

PURPOSE

To investigate the respective diagnostic accuracies of the different breast imaging modalities, i. e., mammography (Mx), high-frequency breast ultrasound (US), and dynamic contrast-enhanced breast (MRI) regarding the early diagnosis of familial (hereditary) breast cancer.

MATERIALS AND METHODS

A prospective, non-randomized controlled clinical multi-center trial is performed at 4 academic tertiary care centers in Germany (Ulm, Munchen/Grosshadern, Munster and Bonn) for a total period of 4 years, sponsored by the German Cancer Aid. The protocol consists of semiannual clinical visits and breast ultrasound, and annual bilateral two-view Mx, US and MRI. Imaging studies were first analyzed independently, then Mx was read in conjunction with US, followed by Mx combined with MRI, and finally, all three imaging modalities were read in synopsis. We present the concept and first results of this trial.

RESULTS

So far, 748 screening rounds are available for analysis in 613 women. A total of 12 breast cancers have been identified, with 11/12 cases in the pTis or pT1/N0 stage. The mean size of detected invasive cancers was 7 mm. A total of 19 benign lesions were biopsied due to false-positive imaging diagnoses. The breast cancer detection rates were: Mx: 5/12 (42 %), US 3/12 (25 %), MRI 10/12 (83 %), and the positive predictive values: Mx 5/17 (29 %), US 3/15 (30 %), and MRI 10/23 (43 %).

CONCLUSION

The preliminary data suggest that early diagnosis of familial breast cancer is feasible by intensified surveillance, in particular with the addition of MRI.

[Automatic injectors in magnetic resonance imaging and computed tomography: pilot study on hygienic aspects]

PURPOSE

To evaluate hygienic conditions using automatic injectors in magnetic resonance imaging (MRI) and computed tomography (CT) during clinical routine.

MATERIALS AND METHODS

The surfaces of medical devices (e. g., control console) and the palms of the technical and medical staff were microbiologically analyzed by taking imprints before and after hygienic education. In addition, the injector syringes for contrast medium (CM) and saline were checked for microbiological contamination following multiple (MRI: 14 h; CT 8 h) and single use. Furthermore, the potential of retrograde contamination from the patient along the tube was analyzed.

RESULTS

A bacterial contamination with typical dermal bacteria was documented for the surfaces of the medical devices, the palms of the technical and medical staff, and the injection syringes following multiple use (MRI: 10/10 CM syringes, 6/10 saline syringes; CT: 8/10 CM syringes, 5/10 saline syringes). Correct hand disinfection in combination with single use of syringes avoided bacterial colonization. Retrograde bacterial contamination from the patient was not observed.

CONCLUSION

Regular hygienic teaching sessions for technical and medical staff in MRI and CT departments using automatic injectors should be mandatory. Furthermore, the multiple use of syringes should be avoided until investigations addressing the potential of bacterial contamination are performed.

[Tubercular spondylitis with retropharyngeal abscess]

In the industrialized countries, the last 15 years have seen an increasing rate of cases of tuberculosis. However, upper cervical spine tuberculosis involving a cold retropharyngeal abscess is extremely rare. We report on a 58 year old female from Sri Lanka presenting with unspecific neck pain and stiffness. She was diagnosed as having extensive tubercular osteodestruction of the second cervical spine body, including epidural and large retropharyngeal abscesses.

Sensitivity of T2-weighted FSE sequences towards physiological iron depositions in normal brains at 1.5 and 3.0�T

To evaluate the sensitivity of T2-weighted fast spin-echo (FSE) sequences to physiological iron depositions in normal brains at MR imaging field strengths of 1.5 and 3.0 T. T2-weighted FSE sequences acquired at 1.5 and 3.0 T clinical imaging systems (Gyroscan Intera, Philips Medical Systems, Best, The Netherlands) were compared by means of MRI in phantoms ( n=6) and healthy volunteers ( n=10). Contrast-to-noise ratios (CNRs) of tubes doped with iron oxides at different concentrations and of brain areas with physiological iron depositions (nucleus ruber, substantia nigra, globus pallidus) were calculated for either field strength. Apparent susceptibility effects of iron-containing brain structures were qualitatively analyzed by comparing the degree of visible hypointensity by a score system at either field strength. The mean CNR of iron oxide tubes and iron-containing brain areas was significantly decreased at 3.0 T. Qualitative analysis confirmed these measurements. Detection and diagnosis of brain disorders with altered iron content such as neurodegenerative parkinsonian disorders (NPD) or intracerebral hemorrhage should benefit from the increased sensitivity of T2-weighted FSE sequences to susceptibility effects at 3.0 T.

Magnetic resonance imaging protocols for examination of the neurocranium at 3 T

The increasing availability of high-field (3 T) MR scanners requires adapting and optimizing clinical imaging protocols to exploit the theoretically higher signal-to-noise ratio (SNR) of the higher field strength. Our aim was to establish reliable and stable protocols meeting the clinical demands for imaging the neurocranium at 3 T. Two hundred patients with a broad range of indications received an examination of the neurocranium with an appropriate assortment of imaging techniques at 3 T. Several imaging parameters were optimized. Keeping scan times comparable to those at 1.5 T we increased spatial resolution. Contrast-enhanced and non-enhanced T1-weighted imaging was best applying gradient-echo and inversion recovery (rather than spin-echo) techniques, respectively. For fluid-attenuated inversion recovery (FLAIR) imaging a TE of 120 ms yielded optimum contrast-to-noise ratio (CNR). High-resolution isotropic 3D data sets were acquired within reasonable scan times. Some artifacts were pronounced, but generally imaging profited from the higher SNR. We present a set of optimized examination protocols for neuroimaging at 3 T, which proved to be reliable in a clinical routine setting.

[The value of magnetic resonance imaging (MRI) for the follow-up of patients with transjugular intrahepatic portosystemic shunts (TIPS)]

PURPOSE

To prospectively determine the value of magnetic resonance imaging (MRI) with flow quantification in the portal vein for the follow-up of patients with transjugular intrahepatic portosystemic shunt (TIPS).

METHODS

Thirty-six patients with TIPS (23 m, 13 f) were evaluated with MR of the liver parenchyma and quantification of flow in the portal vein. MR examinations were correlated with Doppler sonography and conventional angiography including measurement of the portal pressure gradient (PPG). In cases of re-interventions (dilatation/stent application) additional examinations with MRI and Doppler sonography were performed.

RESULTS

MR flow measurements in the portal vein correlated with Doppler sonography (r = 0.69) whereas no correlation of both methods with the PPG was found. No threshold velocity in the portal vein could be determined to predict shunt stenosis. All shunt occlusions (n = 5) were diagnosed correctly by MRA. Thirty measurements before and after successful angiographic interventions revealed a significant increase in portal flow velocity and a significant decrease of the PPG. Magnetic resonance images enabled a reliable detection of procedural complications (parenchymal bleedings, n = 31; extra and subcaspular hematomas, n = 2 each) and newly occurring hepatocellular carcinomas (n = 2) in the follow-up period.

CONCLUSION

Magnetic resonance imaging in the follow-up of TIPS enables a morphological assessment of the liver and an accurate velocity mapping, but is not suited to predict shunt dysfunction as a single method.

Amperometric creatinine biosensor for hemodialysis patients

BACKGROUND

Creatinine is an important clinical laboratory parameter for the evaluation of kidney function. It is essential to determine its concentration in serum of patients suffering from renal insufficiency. During hemodialysis treatment, the measurement of creatinine in the effluent dialysate or ultrafiltrate may give additional information on the efficiency of the extracorporal procedure. Therefore, enzyme sensors with co-immobilized creatinine amidohydrolase, creatine amidinohydrolase and sarcosine oxidase have been used to determine creatinine.

METHODS

Enzymatically generated hydrogen peroxide has amperometrically been detected at a platinum-working electrode. To exclude electroactive compounds of the sample matrix, which might interfere with the electrochemical measurement, the sensors have additionally been modified by a Nafion membrane.

RESULTS

Such sensors showed a linear detection range of 0.06-1.7 mg/dl for creatinine. Diluting the sample with measuring buffer, it has also been possible to measure pathological creatinine concentrations up to 11 mg/dl. A good correlation between creatinine concentrations in serum, dialysate and ultrafiltrate determined by the presented enzyme sensors and those obtained by both, conventional colorimetric Jaffé and enzymatic measurements have been achieved.

CONCLUSION

Further developments will aim at the integration of this measuring principle into the concept to low-cost disposable planar sensors.

Three-dimensional contrast-enhanced MR angiography of endovascular covered stents in patients with peripheral arterial occlusive disease

OBJECTIVE

Three-dimensional contrast-enhanced MR angiography was performed to study MR characteristics of Hemobahn devices.

MATERIALS AND METHODS

Changes in endoluminal signal intensities and the precision of the endoluminal diameter measurement were investigated in phantom studies for different concentrations of gadopentetate dimeglumine. Before and after the Hemobahn devices had been implanted, 10 patients with peripheral arterial occlusive disease were examined on MR imaging and three-dimensional contrast-enhanced MR angiography.

RESULTS

Phantom experiments using three-dimensional MR angiography showed stent-related signal void as a dark ring in the axial image orientation, providing a precise delineation of the stent--vessel border (mean endoluminal diameter, 8.2 mm; SD, 0.6 mm). Changes in endoluminal signal intensity were evaluated quantitatively. Stent-related artifacts did not compromise diagnostic imaging quality. All Hemobahn devices were found to be patent without migration of an implanted graft. In one patient, an extensive perigraft reaction (edema and contrast-enhanced perivascular tissue) was postinterventionally detected on MR imaging and corresponded to clinically evident postimplantation symptoms.

CONCLUSION

Three-dimensional contrast-enhanced MR angiography is a suitable tool to follow up the implantation of Hemobahn devices and to detect intra- and extraluminal abnormalities.

Renal tolerance of a neutral gadolinium chelate (gadobutrol) in patients with chronic renal failure: results of a randomized study

PURPOSE

To assess the renal tolerance of 1.0 mol/L gadobutrol as an electrically neutral contrast agent at magnetic resonance (MR) imaging in patients with impaired renal function.

MATERIALS AND METHODS

Twenty-one patients with impaired renal function were enrolled in this prospective randomized study and classified into two subgroups according to their creatinine clearance: group 1 (n = 12), less than 80 mL/min (<1.33 mL/sec) and greater than 30 mL/min (>0.50 mL/sec); group 2 (n = 9), less than 30 mL/min (<0.50 mL/sec) and not requiring dialysis. Gadobutrol (1.0 mol/L) was injected intravenously at randomly assigned doses of either 0.1 or 0.3 mmol per kilogram of body weight. Changes in vital signs, clinical chemistry, and urinalysis results, including creatinine clearance, were monitored before, at 6 hours, and then every 24 hours until 72 hours (group 1) or 120 hours (group 2) after intravenous injection of gadobutrol. Hematologic results were checked every other day.

RESULTS

No serious adverse event occurred, and no clinically relevant changes in vital signs, hematologic results, clinical chemistry, or urinalysis results were detected in the observation period. Markers for glomerular filtration (creatinine, cystatin C, beta2-microglobulin, creatinine clearance) and tubular function (N-acetyl-beta-D-glucosaminidase, alpha1-microglobulin) were unaffected by gadobutrol in both groups.

CONCLUSION

Gadobutrol did not affect renal function and, therefore, proved to be a safe MR contrast agent in patients with impaired renal function. Even in patients with marginal excretory function (creatinine clearance, <30 mL/min [<0.50 mL/sec]), prehydration or treatment with diuretics or hemodialysis are not required after the administration of gadobutrol.

[MRI study of left ventricular function in patients with coronary disease and myocardial dysfunction before and after coronary revascularization]

PURPOSE

To evaluate left ventricular (LV) myocardial function in ten patients with coronary artery disease (CAD) preoperatively and 6 months after coronary bypass grafting (CABG) by cardiac MRI.

MATERIAL AND METHODS

Ten patients (mean 65.2 +/- 5.9 years) with angiographically proven CAD and an indication for elective CABG underwent prospective evaluation of global LV function and regional wall motion by Cine-MRI at rest using a multiphase FLASH-2D sequence following regions of interest (ROI)-defined diagnostics of regional myocardial wall motion by means of levocardiography. Within the ROIs a total of 613 LV myocardial segments were analyzed preceding and following surgical revascularization. Results were compared with the data of 10 healthy volunteers.

RESULTS

Preoperatively, patients showed reduced stroke volume and ejection fraction compared with volunteers (p < 0.01). Enddiastolic wall thickness (EDWT) and systolic wall thickening (SWT) were significantly lower in the patients (p < 0.01). Based on preoperative levocardiography ROI-defined myocardial segments showed a significantly lower preoperative EDWT in areas with wall motion abnormalities (7.4 +/- 2.5 mm; p < 0.01) than in normal myocardium (9.2 +/- 2.1 mm). Ejection fraction (p < 0.05), endsystolic wall thickness, and SWT (p < 0.01) improved significantly after bypass surgery. On ROI-defined analysis myocardial segments with impaired preoperative wall motion (n = 243) showed a significant increase of EDWT, ESWT and SWT (p < 0.01).

CONCLUSION

In patients with CAD, cardiac MRI enables the non-invasive determination of postinfarctional LV remodeling with an increased EDWT of myocardial segments with normal regional wall motion and of the improvement in global and regional myocardial function following coronary bypass surgery.

[Gd-BOPTA enhanced excretory MR urography without administration of diuretics]

PURPOSE

To evaluate the feasibility and clinical utility of Gd-BOPTA enhanced excretory magnetic resonance urography without additional administration of diuretics in correlation with conventional urography.

METHOD

15 preoperative patients with pelvic tumors were examined at 1.5 T using a breath-hold high-resolution 3D-FLASH sequence during first-pass as well as 5, 10, 15 minutes after i.v. injection of 0.05 mmol/kg BW Gd-BOPTA (MultiHance) without administration of diuretics. Post-processed coronal and multiplanar MIP reconstructions were compared to conventional excretory urography with regard to morphologic accuracy, anatomic variability, filling defects, cause and level of obstruction or compression, tumor visibility, and time-effectiveness by two independent radiologists.

RESULTS

Visualization of the urinary tract by MRU was comparable to conventional excretory urography in 14 of 15 cases. Caliceal fornices were better delineated on conventional urographies, whereas MRU was considered superior in the assessment of the inferior ureter sections, the urinary bladder and obstructive tumors, whose extents could be clearly marked out. Examination times of both techniques were comparable.

CONCLUSION

These first results show that non-diuretic Gd-BOPTA enhanced MRU is comparable to conventional excretory urography for the preoperative diagnosis of pelvic tumors. Further improvements of this technique seem possible by optimization of examination intervals and injection doses.

Reduced iopromide elimination in hemodialysis with cuprophan membranes

PURPOSE

To evaluate the influence of different membrane materials on the efficiency of iopromide elimination.

MATERIAL AND METHODS

Twenty stable patients with chronic renal failure after coronary angiography were investigated for contrast medium elimination during hemodialysis directly after contrast medium application.

RESULTS

Clearance during hemodialysis with cuprophan membranes was 102 +/- 7 mg/ml in contrast to 153 +/- 4 mg/ml in polysulfone membranes. Elimination half-time was 94 +/- 5 min in cuprophan and 79 +/- 3 min in polysulfone membranes, and the elimination rate after 120 min was 59 +/- 2% and 66 +/- 1.5% respectively. Plasma clearance of iopromide was elevated in polysulfone membranes (188 +/-17 ml/min); however, not significantly different to cuprophane membranes (153 +/-11 ml/min). Accordingly, 24-h urinary iopromide excretion was reduced to 26 +/- 4 g/24 h vs. 32 +/- 7 g/24 h.

CONCLUSION

Hemodialysis for iopromide elimination with polysulfone membranes is more effective than with cuprophan membranes.

Influence of dialysis procedure, membrane surface and membrane material on iopromide elimination in patients with reduced kidney function

Haemodialysis for the elimination of contrast medium in patients with advanced renal failure is a common procedure. Even though sufficient elimination with the use of regular low-flux membranes is documented, large differences in results have been reported in prior investigations. We, therefore, compared Cuprophan and polysulfone dialysers with different surface areas to haemofiltration with different amounts of substitution fluid in 40 patients with compromised renal function after coronary angiography. Plasma iodine concentrations were measured by fluorescent excitation analysis. At constant blood flow rates of 200 ml/min, Cuprophan membranes with 1. 3 m(2) surface area had a clearance rate of 87 ml/min, whereas polysulfone membranes of comparable size displayed a significantly higher clearance rate of 147 ml/min. Polysulfone membranes with 1.8 m(2) surface area showed a small but insignificant increase in the iodine clearance (162 ml/min), while Cuprophan membranes displayed an increase in clearance rates (121 ml/min). Additional ultrafiltration led to a further increase in the plasma clearance of both membranes and reduced urinary iodine excretion. Haemofiltration was comparable to haemodialysis in terms of efficacy and thus represents an alternative method. Clearance of iopromide during haemodialysis with polysulfone membranes is higher than with Cuprophan membranes. Elimination rates can be further increased by additional ultrafiltration. Haemofiltration is comparable to haemodialysis regarding contrast medium elimination.

Detection of articular cartilage lesions: experimental evaluation of low- and high-field-strength MR imaging at 0.18 and 1.0 T

The objective of this study was to compare the diagnostic performance of a dedicated orthopedic magnetic resonance (MR) imaging system (0.18 T) and a conventional MR imaging system (1.0 T) in the detection of articular cartilage lesions. Fifty knee joint specimens of pigs with artificially created articular cartilage lesions of different diameters, grades (2-3), and localizations, as well as 50 joints with intact articular cartilage, were imaged at 0. 18 and 1.0 T. Diagnostic performance was determined by means of receiver operating characteristics (ROC) analysis with three independent observers. For none of the pulse sequences used at 0.18 T or 1.0 T areas under ROC curves (A(z)) showed significant differences between the three observers. A(z) values from averaged data were as follows: a) 0.18 T: T1-weighted spin echo (SE): 0.70, proton-density-weighted SE: 0.59, T2-weighted SE: 0.61, two-dimensional (2D) gradient-echo (GRE): 0.73, 3D GRE: 0.75; and b) 1.0 T: T1-weighted SE: 0.73, fat-suppressed T2-weighted turbo-SE: 0. 79, 2D fast low-angle shot (FLASH): 0.79, fat-suppressed 3D FLASH: 0. 96, and water-excited 3D double-echo steady state (DESS): 0.96. With the use of 3D pulse sequences, the high-field system demonstrated a significantly better diagnostic performance than the low-field system in the detection of grades 2 and 3 articular cartilage lesions (P < 0.001).