Biomedical subjects

C C Nolte-Ernsting

Publications and source records attributed to C C Nolte-Ernsting.

17 recordsLinked to original sources

PubMed2001

Diuretic-enhanced gadolinium excretory MR urography: comparison of conventional gradient-echo sequences and echo-planar imaging.

The aim of this study was to investigate the utility of different gadolinium-enhanced T1-weighted gradient-echo techniques in excretory MR urography. In 74 urologic patients, excretory MR urography was performed using various T1-weighted gradient-echo (GRE) sequences after injection of gadolinium-DTPA and low-dose furosemide. The examinations included conventional GRE sequences and echo-planar imaging (GRE EPI), both obtained with 3D data sets and 2D projection images. Breath-hold acquisition was used primarily. In 20 of 74 examinations, we compared breath-hold imaging with respiratory gating. Breath-hold imaging was significantly superior to respiratory gating for the visualization of pelvicaliceal systems, but not for the ureters. Complete MR urograms were obtained within 14-20 s using 3D GRE EPI sequences and in 20-30 s with conventional 3D GRE sequences. Ghost artefacts caused by ureteral peristalsis often occurred with conventional 3D GRE imaging and were almost completely suppressed in EPI sequences (p < 0.0001). Susceptibility effects were more pronounced on GRE EPI MR urograms and calculi measured 0.8-21.7% greater in diameter compared with conventional GRE sequences. Increased spatial resolution degraded the image quality only in GRE-EPI urograms. In projection MR urography, the entire pelvicaliceal system was imaged by acquisition of a fast single-slice sequence and the conventional 2D GRE technique provided superior morphological accuracy than 2D GRE EPI projection images (p < 0.0003). Fast 3D GRE EPI sequences improve the clinical practicability of excretory MR urography especially in old or critically ill patients unable to suspend breathing for more than 20 s. Conventional GRE sequences are superior to EPI in high-resolution detail MR urograms and in projection imaging.

Adult↗

PubMed2001

MR urography: examination techniques and clinical applications.

Modern MR urography is performed on the basis of two different imaging strategies, which can be used complementarily to cover almost all aspects in the diagnosis of upper urinary tract diseases. The first technique utilizes unenhanced, heavily T2-weighted pulse sequences to obtain static-fluid images of the urinary tract. T2-weighted MR urograms have proved to be excellent in the visualization of the markedly dilated urinary tract, even if the renal excretory function is quiescent. Static-fluid MR urography is less suitable for imaging of disorders that occur in the nondilated collecting system. The second MR urography technique is analogous to the methodology of conventional intravenous pyelography and is, therefore, designated as excretory MR urography. For this purpose, a non-nephrotoxic gadolinium chelate is intravenously administered and after its renal excretion, the gadolinium-enhanced urine is visualized using fast T1-weighted gradient-echo sequences. The combination of gadolinium and low-dose furosemide (5-10 mg) is the key for achieving a uniform distribution of the contrast material inside the entire urinary tract and, secondly, to avoid high endoluminal gadolinium concentrations, which cause signal loss of the urine due to T2* effects. Gadolinium excretory MR urography allows to obtain high-quality images of both nondilated and obstructed urinary tracts in patients with normal or moderately impaired renal function. This article reviews the principles of T2- and T1-weighted MR urography in detail and informs how to use these techniques safely in potential clinical applications such as chronic urolithiasis, intrinsic and extrinsic tumor diseases, and congenital anomalies. Magnetic resonance urography performed in combination with standard MR imaging offers a potential to reduce the need for invasive retrograde pyelography. Although the economic aspect is still problematic, it is obvious that MR urography will continue to increase its role in clinical uroradiology.

Female↗

PubMed2001

MR-guided percutaneous drainage of abdominal fluid collections in combination with X-ray fluoroscopy: initial clinical experience.

The aim of this study was to examine the feasibility of a hybrid interventional MR system, which combines a closed bore magnet with a C-arm fluoroscopy unit for percutaneous drainage of abdominal fluid collections. During the past 2 years, we have performed four drainage procedures in four patients (mean age 47 years). Three patients had abscesses (psoas muscle, kidney, subphrenic location) and the fourth patient had a recurrent splenic cyst. All procedures were performed on an interventional MR system consisting of a 1.5-T ACS-NT scanner combined with a specially shielded C-arm. The drainages were guided by T1-weighted fast gradient-echo images, T2-weighted single-shot turbo spin-echo images or both. A standard 18 G (1.2 mm) nonferromagnetic stainless steel needle with a Teflon sheath was used for the punctures following which a 0.89 mm nitinol guidewire was inserted into the fluid collection. Thereafter, the patient was positioned in the immediate adjacent fluoroscopy unit and a drainage catheter was placed under fluoroscopic control. All drainage catheters were successfully placed into the fluid collections, as proven by fluid aspiration and resolution of the collection. The mean time needed for the entire drainage procedure (MR and fluoroscopy) was 110 min. No procedure-related complications occurred. It is feasible to perform drainage procedures on a closed-bore MR scanner. The multiplanar imaging capabilities of MR are particularly helpful for fluid collections in the subphrenic location.

Abdominal Abscess↗

PubMed2001

US-guided nephrostomy with the aid of a magnetic field-based navigation device in the porcine pelvicaliceal system.

PURPOSE: To assess the technique and feasibility of ultrasound (US)-guided nephrostomy performed with the aid of a magnetic field-based navigation device. MATERIALS AND METHODS: Twelve percutaneous nephrostomy procedures were performed in seven domestic pigs under real-time US guidance employing a navigation system. Two magnetic field sensors registered the actual position of the puncture needle and the US transducer. The actual needle position and the aimed puncture tract were graphically projected into the real-time US images, allowing exact navigation of the needle. After placement of the needle into the renal pelvis, the nephrostomy tube was inserted by means of the Seldinger technique. RESULTS: The puncture procedure was successfully performed in each case. The renal pelvis was punctured in a single attempt in 10 of 12 cases. In two cases, multiple attempts were necessary because bending of the puncture needle led to inaccuracies of the navigation system. With exception of two small perirenal urinomas, no complications were seen. CONCLUSIONS: The magnetic field-based navigation device allows easy and accurate performance of nephrostomy guided solely by US.

Animals↗

PubMed2001

Multi-slice CT urography after diuretic injection: initial results.

PURPOSE: To investigate the feasibility of CT urography (CTU) using a multi-slice (MS) scanner and to find out whether a low-dose diuretic injection is advantageous for the opacification of the urinary tract. METHODS: MS-CTU was performed in 21 patients with urologic diseases. In 5/21 patients, 250 ml of physiologic saline Solution were injected. In 16/21 patients, 10 mg of furosemide were injected 3-5 min before contrast material administration. A 4 x 2.5 mm collimation with a pitch of 1.25 and a tube current of 100-150 mA were used. Scan time was 12-16 sec. 3 mm thin axial images with an overlap of 67% were reconstructed. Multiplanar maximum intensity projection (MIP) images were postprocessed to obtain urographic views. Bone structures were eliminated using the volume-of-interest method. RESULTS: Furosemide-enhanced MS-CTU achieved either near complete or complete opacification in 30/32 (94%) ureters and in 32/32 (100%) pelvicaliceal systems up to a serum creatinine of 150 mumol/l. In our series, only one CTU scan per patient was needed to obtain a diagnostic urogram after 10 min of contrast material injection. Ureteral compression was not necessary. When physiologic saline solution was used instead of furosemide, the radiopacity inside the enhanced pelvicalices was 4-5 times higher and more inhomogeneous. Diuretic-enhanced MS-CTU was more accurate in the depiction of pelvicaliceal details. In combination with furosemide, calculi were well identified inside the opacified urine and were safely differentiated from phleboliths. Postprocessing times of up to 20 minutes were problematic as were contrast-enhanced superimposing bowel loops on MIP images. CONCLUSION: Preliminary results demonstrate a good feasibility of furosemide-enhanced MS-CTU for obtaining detailed visualization of the entire upper urinary tract.

Adult↗

PubMed2000

MRI of the inner ear: comparison of axial T2-weighted, three-dimensional turbo spin-echo images, maximum-intensity projections, and volume rendering.

RATIONALE AND OBJECTIVES: To compare the ability of axial T2-weighted, three-dimensional, turbo spin-echo (3D TSE) images, targeted maximum-intensity projections (MIPs), and 3D volume reconstructions to depict anatomic details of the labyrinth. METHODS: In 24 volunteers, 3D TSE images were obtained. MIPs and 3D volume reconstructions were performed from the acquired data. All images were evaluated by three radiologists independently regarding the visualization of the different anatomic structures. RESULTS: In the axial slices, most anatomic details were visible in comparison with observations by the other modalities. The 2.5 windings of the cochlea were best depicted on the MIPs. Volume reconstructions rendered excellent spatial information regarding the vestibule and semicircular canals and were the only technique that demonstrated all three ampullae in all cases. CONCLUSIONS: Axial TSE images, MIPs, and 3D volume reconstructions are complementary modalities that provide different information. Our results suggest that improved diagnostic information can be obtained by applying these volume visualization reconstruction techniques.

Adult↗

PubMed2000

Feasibility and utility of respiratory-gated, gadolinium-enhanced T1-weighted magnetic resonance urography in children.

RATIONALE AND OBJECTIVES: To evaluate the feasibility and utility of respiratory-gated, gadolinium-enhanced T1-weighted magnetic resonance (MR) urography in children. METHODS: In a prospective study, 30 consecutive children, aged 3 weeks to 13.8 years, underwent MR urography. After intravenous injection of low-dose furosemide and gadopentetate dimeglumine, respiratory-gated, coronal, T1-weighted 3D-gradient-echo sequences were obtained at 1.5 T 5 to 30 minutes after contrast administration. Postprocessing of the data was performed using a maximum-intensity projection algorithm. In addition, precontrast half-Fourier rapid acquisition with relaxation enhancement MR urograms were obtained in 29 children. RESULTS: Respiratory-gated, T1-weighted MR urography was successfully performed in all children without the need for sedation. Compared with the final diagnosis, prospective analysis of MR urography images revealed the correct diagnosis in 56 of 58 pelvicaliceal systems (96%). The ureteral morphology was correctly evaluated in 59 of 64 ureters (92%). The method showed limited efficiency for evaluating nonfunctioning renal units. CONCLUSIONS: Respiratory-gated, gadolinium-enhanced T1-weighted MR urography is a feasible and effective diagnostic tool in the assessment of upper urinary tract morphology in children. It is especially useful in depicting nondilated collecting systems and ureters.

Adolescent↗

PubMed1999

[Virtual endoscopy of the upper urinary tract based on contrast-enhanced MR urography data sets].

PURPOSE: To investigate the feasibility of reconstructing a virtual endoscopy from MR imaging data sets of the upper urinary tract. METHOD: The data obtained from 28 contrast-enhanced MR urographic examinations (5 normal; 23 pathologic) were post-processed to reconstruct a virtual ureterorenoscopy (VURS) using a threshold image segmentation. The visualization of the upper urinary tract was based on the acquisition of T1-weighted 3D gradient-echo sequences after intravenous administration of gadolinium-DTPA and a prior injection of low-dose furosemide. RESULTS: The employed MR urography technique created in all 28 cases a complete and strong contrast enhancement of the urinary tract. These 3D sequence data allowed the reconstruction of a VURS, even when the collecting system was not dilated. The best accuracy was provided by the MR urography sequences with the smallest voxel size. Moreover, the data acquisition based on a breath-hold technique has proved superior to that using a respiratory gating. Inside the renal pelvis, all calices could be assessed by turning the virtual endoscope in the appropriate direction. The visualization of the ureteral orifices in the bladder was also possible. All filling defects that were diagnosed by MR urography could be evaluated from the endoluminal view using the VURS. The exact characterization of the lesions based only on the assessment of the surface structure was difficult. CONCLUSION: A virtual endoscopy of the upper urinary tract can be successfully reconstructed using the data sets of high-resolution 3D MR urography sequences.

Adult↗

PubMed1998

[MR-micturating cystourethrography using radical k-space sampling].

PURPOSE: To investigate the feasibility of micturating cystourethrography (MCU) by means of real-time MR imaging with radial k-space sampling. METHODS: The MR-MCU was performed in 7 adult male patients subsequent to a gadolinium(Gd)-DTPA-enhanced excretory MR-urography. The Gd-enhancement of the urethra was visualized by MR-fluoroscopy using a T1-weighted gradient-echo-sequence with radial k-space sampling and a slice thickness of 10 mm. RESULTS: The proposed technique allowed in all 7 patients a dynamic realtime imaging of the Gd-flow inside the urethra during micturition. The normal anatomy of the entire course of the urethra was demonstrated in each patient, while simultaneously the relation to the prostate and pelvic floor became visible. Furthermore, the urinary bladder could be assessed by interactive repositioning of the slice orientation in any preferred direction. The ureters could also be visualized due to the persisting Gd-enhancement of the upper urinary tract after the preceding MR-urography. CONCLUSIONS: MR-MCU using Gd-DTPA and radial k-space data acquisition is a novel imaging modality for a real-time visualization of the urethra during micturition without radiation exposure. This method also allows the assessment of the bladder, the pelvic floor, and the Gd-filled upper urinary tract which suggests a potential for the diagnosis of vesicoureteral reflux and urinary incontinence.

Adult↗

PubMed1998

[MRI-guided percutaneous nephrostomy of the contrast-enhanced, nondilated upper urinary tract: initial experimental results].

PURPOSE: To evaluate technique and practicability of MR-guided percutaneous nephrostomy (MRPCN) in an animal model. METHODS: In three domestic pigs, a unilateral percutaneous nephrostomy tube was placed into the nondilated collecting system using exclusively MR-guidance with a standard 1.5 T scanner. The urinary tract was visualized by intravenous injection of Gd-DTPA and low-dose furosemide. The entire interventional procedure was controlled using a T1-weighted "dual stack" 2 D TFE sequence in two orthogonal planes. RESULTS: In all three animals, the puncture needle was safely directed into the nondilated target calyx. Even slight deviations of the needle from the optimal path were readily detected on both MR image planes which enabled immediate correction. This technique successfully achieved a "first attempt" puncture of the targeted calyx in each animal. Over a nitinol guidewire a 5 F catheter was placed into the renal pelvis. Its dysprosium labelled tip was accurately delineated on contrast-enhanced MR images. CONCLUSIONS: Percutaneous nephrostomy under MR guidance is a very feasible technique for puncturing the nondilated pelvicalyceal system. This procedure offers some advantages over the current standard modalities.

Animals↗

PubMed1998

[Real-time MRI with radial k-radial scanning technique for control of angiographic interventions].

PURPOSE: To test the feasibility of real-time MR controlled guidance of field-inhomogeneity catheters in vitro and in vivo as a first step to MR-guided angiographic interventions. METHODS: Applying a combination of radial scanning with the sliding window reconstruction technique, a frame rate of 23 low resolution images per second was achieved. Field inhomogeneity catheters were steered through a flow phantom and into the renal arteries of a pig. RESULTS: It was possible to visualize flow or, respectively, vessels and to depict catheter movements. This enabled real-time MR-guidance of the catheter into the renal arteries of the flow phantom and into those of the pig. CONCLUSIONS: The new technique yields a sufficiently high temporal resolution for MR-guidance of catheters through vessels.

Angiography↗

PubMed1998

Gadolinium-enhanced excretory MR urography after low-dose diuretic injection: comparison with conventional excretory urography.

PURPOSE: To evaluate the clinical utility and morphologic accuracy of gadolinium-enhanced excretory magnetic resonance (MR) urography after low-dose diuretic injection and to correlate the results with those of conventional urography. MATERIALS AND METHODS: In 71 patients with urologic symptoms, excretory MR urography was performed after intravenous injection of 5-10 mg furosemide and, 30-60 seconds later, 0.1 mmol of gadopentetate dimeglumine per kilogram of body weight. The MR urograms were interpreted by three radiologists, who were blinded to the clinical outcome, and subsequently compared with conventional urograms. RESULTS: Injection of furosemide before contrast material led to rapid, uniform gadolinium distribution inside a sufficiently distended collecting system such that there was no excessive concentration of gadolinium in the urine. In patients with normal or moderately reduced excretory function, this effect allowed complete visualization of the urinary tract within 5-20 minutes of contrast material injection while minimizing gadolinium-related endoluminal T2* effects. The clinical course helped verify almost all MR urographic results. The MR urographic technique was significantly superior to conventional urography in the assessment of the ureters and bladder (P < .0001). Delineation of small caliceal abnormalities is still problematic. The best depiction of the pelvicaliceal system was obtained with fat-suppressed MR imaging, although it was still slightly inferior to conventional urography (P < .05). CONCLUSION: Gadolinium-enhanced excretory MR urography performed after low-dose diuretic injection is a promising and accurate alternative to conventional excretory urography for imaging the morphology of the urinary tract.

Adult↗

PubMed1997

[Flow direction-sensitive spin-echo MR angiography].

New blood pool contrast agents yield a significant shortening of T1 of blood. Consequently, the usual techniques of time-of-flight and phase-contrast angiographies cannot produce angiograms sensitive to one flow direction, even if saturation slabs are applied. It was our aim to test the hypothesis of displaying arterial and venous flow selectively with a specially designed spin echo sequence even after administration of contrast agents. Parallel slice selective 90-degree and 180-degree pulses were applied. The distance between slices could be varied. It was attempted to obtain MR angiographies that were flow sensitive for one direction only. We performed flow phantom studies without the use of contrast media and first in vivo experiments in pigs after administration of iron oxide particles. With our modified spin echo sequence unidirectional flow can be displayed, whereas stationary tissue is totally suppressed. There are no special demands for the hardware and no additional postprocessing needs to be performed. The locally off-centred 90-degree and 180-degree pulses are responsible for this. Exclusively, protons excited by the 90-degree pulse and flowing into the slice of the 180-degree pulse will be refocused and only such protons will give rise to signal in the images.

Animals↗

PubMed1996

Optimizing joint imaging: MR imaging techniques.

For optimizing MR imaging of the joints, a sophisticated knowledge of MR system hard- and software conditions and coil technologies, sequence and contrast preparation techniques, and the use of paramagnetic contrast agents is necessary. This review article discusses the basic principles of the appropriate use of surface coils as well as the different conventional and fast imaging sequences, including three-dimensional (3D) MR imaging. In addition, the applications of contrast agents as well as the most important contrast preparation techniques are reviewed.

Humans↗

PubMed1996

MRI of degenerative bone marrow lesions in experimental osteoarthritis of canine knee joints.

OBJECTIVE: The objective of this study was to determine the value of MRI in the detection of degenerative bone marrow abnormalities in an animal osteoarthritis model. DESIGN: In 10 dogs with experimentally induced unilateral osteoarthritis of the knee, MRI was performed using two-dimensional spin-echo (2D-SE) and three-dimensional gradient-echo (3D-GE) imaging. Contrast enhanced T1-weighted 2D-SE sequences were also obtained after injection of gadolinium-DTPA. The results were compared with the gross and histopathologic findings and with radiography. RESULTS: Histopathologic specimens revealed 21 osteosclerotic lesions and 5 intraosseous cysts. On 2D-SE images, 24 of 26 lesions were detected, while 21 of 26 lesions were identified on 2D-GE sequences. Radiography, including conventional tomography, demonstrated 9 of 26 lesions. Regardless of the sequence weighting, all osteosclerotic lesions appeared hypointense on MRI. Signal loss in bone sclerosis resulted primarily from the reduction of intact fat marrow, the increased bone density being of secondary importance. Quantitative signal analysis allowed approximate estimation of the grade of sclerosis. On postcontrast images, sclerotic bone remained hypointense, although significant but non-specific enhancement relative to the normal fat marrow was observed. The extent of contrast enhancement did not correlate with the grade of osteosclerosis. All five cysts were readily diagnosed by MRI. Cysts displayed either central or marginal contrast enhancement within their cavities. CONCLUSIONS: MRI provides a sensitive method for the diagnosis of osteoarthritic bone abnormalities, allowing their differentiation from most non-degenerative subarticular lesions.

Animals↗

PubMed1995

[The MRT of osteophytosis in experimental gonarthrosis].

PURPOSE: The value of MRI for the detection of knee osteophytosis was determined in an animal osteoarthritis model. METHODS: 10 dogs with experimentally induced unilateral osteoarthritis of the knee were investigated with MRI including 2-D-spin echo (SE) and 3-D-gradient echo (GE) imaging. The results were correlated with gross and histopathologic findings and with radiography. RESULTS: Osteophyte formation appeared early in the osteoarthritic process. Pathological analysis yielded 65 osteophytes. With 3-D-GE imaging, 91% of the osteophytes were detected, while 68% were visible on 2-D-SE images. With two-level radiography, 43% of the osteophytes were diagnosed. Additional use of tunnel view and conventional tomography increased the detection rate to 65%. Independent of the imaging technique, MRI revealed three different signal patterns of the osteophyte bone structure. Compared with the histologically evident fat marrow content and the grade of bone sclerosis, best agreement was achieved with 2-D-SE sequences. However, a discrepancy remained in 22%. A fibrocartilaginous layer at the osteophyte surface could be delineated especially on 3-D-GE images. CONCLUSIONS: MRI provides the highest standard in non-invasive diagnosis of osteophytes in the knee. 3-D-GE imaging in particular can demonstrate early and small osteophyte formation.

Animals↗

PubMedDate not supplied

MR imaging-guided percutaneous nephrostomy and use of MR-compatible catheters in the nondilated porcine urinary tract.

PURPOSE: To investigate technique and practicability of MR-guided percutaneous nephrostomy (MRPCN) and to test magnetic resonance (MR)-compatible catheters inside the urinary tract. MATERIALS AND METHODS: In 10 healthy pigs, a percutaneous nephrostomy tube was placed into the nonobstructed pelvicaliceal system with use of exclusive MR guidance with a standard 1.5-T magnet. The urinary tract was visualized by intravenous injection of Gd-DTPA in combination with low-dose furosemide. The procedure was controlled with use of a T1-weighted turbo gradient-echo sequence in two orthogonal planes. The equipment for MRPCN included an 18-gauge MR-compatible puncture needle, a nitinol guide wire, and different 5-F MR catheters. RESULTS: In all 10 animals, the puncture needle was safely directed into the nondilated target calix. Slight deviations of the needle were detected on both MR image planes, which enabled immediate correction. This technique achieved a "first attempt" puncture of the targeted calix in each animal. MR images accurately demonstrated the dysprosium labelled tip of the different inserted catheters. It proved essential to inject a gadolinium-insaline solution via these catheters to preserve the endoluminal contrast enhancement as long as necessary. Balloon catheters were directed and inflated inside the ureter under exclusive MR guidance. Complications such as perforation and leakage were visualized by MR imaging. CONCLUSIONS: MRPCN is a promising technique for puncturing the pelvicaliceal system. The ability to successfully enter the urinary tract, even when it is nondilated, underscores the accuracy achievable with multiplanar MR imaging.

Animals↗