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Biomedical subjects

Elmar M Merkle

Publications and source records attributed to Elmar M Merkle.

At least 19 recordsLinked to original sources
PubMed2007

Abdominal pain: coronal reformations from isotropic voxels with 16-section CT--reader lesion detection and interpretation time.

PURPOSE: To retrospectively assess if reader detection of intraabdominal pathologic findings on coronal reformations from isotropic voxels at 16-section computed tomography (CT) was similar to reader detection on transverse scans. MATERIALS AND METHODS: The institutional review board approved this HIPAA-compliant study, and a waiver of informed consent was obtained. Twenty-nine consecutive patients (12 men, 17 women; mean age, 48 years; age range, 21-93 years) with abdominal pain underwent 16-section CT with coronal reformations. Eight independent readers reviewed randomized scans (transverse and coronal) and identified pathologic findings in multiple organ systems. Timing for each interpretation was recorded. One month later, readers reviewed the scan reformatted in the other imaging plane. Agreement between transverse and coronal scans was measured by using Cohen kappa coefficients. RESULTS: Agreement was moderate to near perfect between transverse and coronal interpretations for intraabdominal anatomic and pathologic findings (kappa=0.59-1.00). For transverse interpretations, more thoracic pathologic findings were noted than for coronal interpretations; for coronal interpretations, more lymph nodes were noted than for transverse interpretations. Mean transverse interpretation time was 4.9 minutes+/-1.1 (standard deviation) (range, 2.9-6.5 minutes); mean coronal interpretation time was 5.1 minutes+/-0.8 (range, 3.3-6.7 minutes). For each reader, there was no statistically significant difference in interpretation time between transverse and coronal scans (P=.06). CONCLUSION: With regard to the presence of intraabdominal pathologic findings, coronal reformations from isotropic voxels are similar to transverse scans in terms of interpretation time and reader agreement.

Abdominal Neoplasms↗
PubMed2006

MR liver imaging and cholangiography in the presence of surgical metallic clips at 1.5 and 3 Tesla.

To evaluate whether clips from prior cholecystectomy impair image quality during magnetic resonance cholangiography (MRC) at 3 Tesla (T) compared with 1.5 T, surgical clips were embedded in a gel phantom and positioned at predefined distances from a fluid-filled tube designed to simulate the bile duct. The maximum clip distance was noted where susceptibility artifacts obscured the fluid-filled tube at 1.5 T and 3 T. Susceptibility artifact size was calculated for each sequence within each magnet class. In vivo analysis included 42 patients postcholecystectomy who underwent MRC at either 1.5 T or 3 T. In vitro, mean area of susceptibility artifacts was 104 mm2 on 3-T and 75 mm2 on 1.5-T MR imaging (MRI). While surgical clips within a 2-mm range impaired visualization of the fluid-filled tube on 1.5-T MRI, this range increased to 4 mm on 3-T MRI. In vivo, MRC image quality was impaired by susceptibility artifacts in three of 21 cases at 3 T and in two of 21 cases at 1.5 T. Overall, biliary pseudo-obstructions due to susceptibility artifacts from cholecystectomy surgical clips were not substantially more common on 3-T MRC in clinical practice, and patients with a history of prior cholecystectomy should not be excluded from a 3-T MRC.

Adult↗
PubMed2006

Pneumobilia: where to look for on hepatic MR imaging?

The presence of pneumobilia is a particular problem in magnetic resonance cholangiopancreatography (MRPC) and may create an appearance that can be mistaken for intraductal stones. Compared with biliary stones, however, pneumobilia causes a susceptibility artifact on hepatic MR imaging and appears as a signal void on a dual echo gradient MR sequence, such as the T1-weighted in-phase and opposed-phase gradient echo sequence. This susceptibility artifact is more pronounced on the gradient echo image with the longer echo time due to the continued decay of the transverse magnetization. Besides identification of hepatic steatosis, the double echo approach is particularly helpful in identification of pneumobilia.

Artifacts↗
PubMed2006

Abdominal magnetic resonance imaging at 3.0 T what is the ultimate gain in signal-to-noise ratio?

RATIONALE AND OBJECTIVES: The purpose of this study was to calculate the gain in signal-to-noise ratio (SNR) of four human abdominal tissues at 3.0 Tesla (T) compared with standard 1.5 T and to validate this calculation in vivo. MATERIALS AND METHODS: The expected gain in SNR at 3.0 T in the liver, pancreas, spleen, and kidney compared with standard 1.5 T was approximated theoretically for a T2-weighted HASTE (half-Fourier acquisition single-shot turbo spin-echo) and a T1-weighted gradient-echo in- and opposed-phase sequence. Fifteen healthy male subjects underwent abdominal MR imaging using a 1.5 T and 3.0 T scanner. Coronal T2-weighted HASTE images and axial T1-weighted gradient-echo in- and opposed-phase images were acquired using the sequence parameters optimized by the vendor. RESULTS: Except for opposed-phased imaging of pancreatic tissue, in vivo adjusted SNR values of all abdominal tissues were significantly higher at 3.0 T for all sequences (P < .05). The highest overall gain in SNR was achieved with the HASTE sequence ranging from 3.8-fold for renal imaging to 7.4-fold for hepatic imaging. The theoretical calculation of SNR gain was in good agreement with the experimentally measured gain in SNR for the HASTE and the in-phase sequence. CONCLUSION: High-field abdominal MR imaging at 3.0 T offers significantly higher SNR compared with standard 1.5 T MR imaging.

Abdomen↗
PubMed2006

Abdominal MR imaging at 3T.

Body MR imaging at 3T is in its infancy, and should improve substantially over the next several years. Radiologists need to be aware of several limitations that are based on the laws of physics: Overall, the gain in SNR at 3T will be less than twofold (without protocol alteration) compared with a standard 1.5T MR system because of the increase in T'I'1 at ultra high field. Typically, the gain in SNR is greater in T2-weighted sequences than in TI-weighted sequences, because longer TRs allow for a more complete recovery of the longitudinal magnetization, and T2 is independent of Bo. Thus, for example, patients who are referred for an MR cholangiography may benefit from an ultrahigh-field MR examination. Chemical shift artifacts of the first kind are twice as large in ultrahigh-field MR imaging compared with standard 1.5T MR imaging. Conversely, chemical shift artifacts of the second kind do not increase in size, although the timing is altered. The increased difference in resonant frequency between water and fat at 3T also is advantageous because it allows for a better separation of the fat and water peak during MR spectroscopy, and allows better or faster fat suppression using chemical shift techniques, such as fat saturation or water excitation. Susceptibility artifacts are approximately twice as large by volume on 3T MR imaging. Although patients who are referred for a "colon" study may be challenging at ultrahigh field, the search for "gas" (eg, free air or pneumobilia) should be easier. Patients with metal implants should undergo an MR examination at 3T only if the metal-containing device specifically has been proved to be MR safe at this field strength. Usually, standing wave and conductivity effects are not seen in body imaging at a field strength of 1.5T. At 3T, these artifacts are most pronounced in pregnant women in the sec-ond and third trimester, because of the large amount of conductive amniotic fluid and the increased size of the abdomen. Therefore, fetal MR imaging generally should not be performed at 3T because of these artifacts and the increased safety concerns. The same holds true for patients with a large amount of ascites, who also are not well suited for an ultrahigh-field MR examination. Except as noted above, most patients can undergo an abdominal MR imaging study at 3T with a reasonable outcome in terms of image quality.

Abdomen↗
PubMed2006

Review of internal hernias: radiographic and clinical findings.

OBJECTIVE: Internal hernias, including paraduodenal (traditionally the most common), pericecal, foramen of Winslow, and intersigmoid hernias, account for approximately 0.5-5.8% of all cases of intestinal obstruction and are associated with a high mortality rate, exceeding 50% in some series. To complicate matters, the incidence of internal hernias is increasing because of a number of relatively new surgical procedures now being performed, including liver transplantation and gastric bypass surgery. A significant increase in hernias is occurring in patients undergoing transmesenteric, transmesocolic, and retroanastomotic surgical procedures. It is important for radiologists to be familiar with and to understand the various types of internal hernias and their imaging features so that prompt and accurate diagnosis of these conditions can be made. CONCLUSION: This article illustrates the imaging findings of internal hernias, with emphasis placed on the CT findings, especially in transmesenteric, transmesocolic, and retroanastomotic types of internal hernias.

Hernia, Abdominal↗
PubMed2006

Abdominal MRI at 3.0 T: the basics revisited.

OBJECTIVE: The purpose of our article is to describe the underlying physics concepts of abdominal MRI at 3.0 T and their impact on signal-to-noise ratio, susceptibility artifacts, chemical shift artifacts, and dielectric effects. CONCLUSION: Abdominal MR sequence protocols optimized for 1.5-T scanners should not be transferred to 3.0 T without substantial modification. In addition, specific patient groups--for example, large patients with ascites--are not well suited to undergo an abdominal MRI study at 3.0 T.

Abdomen↗
PubMed2005

Roux-en-Y gastric bypass for clinically severe obesity: normal appearance and spectrum of complications at imaging.

Surgery currently appears to be the most effective method to curtail the effects of morbid obesity and all of its comorbid conditions. Although the ideal procedure has yet to be devised, Roux-en-Y gastric bypass has proved to be successful for many morbidly obese patients pursuing weight loss and increased health. As the technical aspects of this procedure become less cumbersome and the patient population increases, it is vital for radiologists to be proficient in the specific evaluation of these patients, in order to provide optimal care. Complications can be minimized, managed more efficiently, or prevented with prompt evaluation by the radiologist. It is important to appreciate the patency of both the gastrojejunostomy and the jejunojejunostomy, as well as adequate progression of contrast material before the patient is discharged (preferably 24-72 hours after surgery). Follow-up complications include anastomotic leak, staple-line disruption, stomal stenosis, occlusion of the Roux limb, small-bowel obstruction due to adhesions or internal hernia, and obstruction of the enteroenterostomy leading to acute gastric distention. These complications may be life threatening, since clinical symptoms are often inconclusive. To achieve optimal outcome, therefore, conventional radiographic and computed tomographic studies should not be delayed.

Anastomosis, Roux-en-Y↗
PubMed2005

The interventional MR imaging suite: magnet designs and equipment requirements.

Soon after the introduction of MR imaging as an imaging tool, researchers began to investigate its capabilities to guide interventional minimally invasive procedures, such as biopsies. These early efforts have encouraged vendors and numerous research groups worldwide to identify clinical problems in the field of image-guided intervention, for which MR imaging is beneficial as an imaging modality, and to develop and refine soft-ware and hardware components to meet the specific requirements of interventional MR imaging. Over nearly 20 years, continuous advances in magnet and system design have accelerated the progress of MR-guided intervention.

Equipment Design↗
PubMed2005

Functional cardiac CT and MR: effects of heart rate and software applications on measurement validity.

This study sought to validate different software applications for cardiac function analysis using ECG-gated CT and MR datasets in correlation with underlying heart rate. Ten patients and a set of ventricular phantoms underwent concurrent multislice-CT and cine-MR imaging for evaluation of cardiac function. Datasets from both imaging modalities were evaluated utilizing 2 volumetric analysis tools to determine left ventricular volume and mass. Initially, intraobserver measurement variability was assessed. Detected measurement variability was correlated with underlying absolute magnitude of cardiac volumes and masses. Subsequently, results were statistically evaluated by determining significant data variability depending on imaging modality and choice of evaluation software. Finally, the data variability was correlated with underlying heart rates. This study showed that all analyzed datasets uniformly presented intraobserver variations below 2%, and variability was not related to the magnitude of measurement. Significant measurement accuracy was proven in all calculated parameters obtained from the cardiac phantoms. Acquired patient datasets and calculated functional parameters showed significant data homogeneity, with measurement variability coefficients ranging from 0.935-0.955. CT datasets showed maximal data variability at heart rates below 60 BpM. MR datasets showed maximal data variability at heart rates above 90 BpM. In conclusion, CT and MR datasets allowed an interchangeable utilization of volumetric analysis tools. However, reliable volumetric analysis was limited to an optimal range of cardiac rates for each modality, thus emphasizing the necessity of reporting volumetric measurement results in combination with heart rate to allow for consideration of this possible cause for measurement variation.

Adolescent↗
PubMed2005

MR imaging follow-up after percutaneous radiofrequency ablation of renal cell carcinoma: findings in 18 patients during first 6 months.

PURPOSE: To prospectively evaluate the magnetic resonance (MR) imaging findings seen within the first 6 months after radiofrequency (RF) thermal ablation of renal cell carcinoma (RCC). MATERIALS AND METHODS: After providing written informed consent, 18 patients (17 men, one woman; mean age, 71.2 years) with RCC underwent MR imaging-guided percutaneous RF thermal ablation, which was performed by using protocols approved by a comprehensive cancer center protocol committee and the institutional review board for human investigation. The study was Health Insurance Portability and Accountability Act compliant. Follow-up unenhanced T2-weighted MR images and unenhanced and gadolinium-enhanced T1-weighted MR images were acquired immediately, 2 weeks, 3 months, and 6 months after ablation. Thermal ablation zone size was analyzed, and contrast-to-noise ratios (CNRs) were calculated from the signal amplitudes of the thermal ablation zone, perirenal fat, and normal renal cortex on the MR images. Statistical analyses were performed by using the paired Student t test. P < .05 was considered to indicate statistical significance. RESULTS: The mean follow-up time was 16.1 months (range, 6.0-41.2 months). The mean sizes of the thermal ablation zones were 6.8, 7.0, 6.1, and 4.7 cm2, respectively, at immediate, 2-week, 3-month, and 6-month follow-up MR imaging examinations. Thermal ablation zones were uniformly hypointense and had a surrounding bright rim on T2-weighted images and were predominantly hyperintense on T1-weighted images. Thin rim enhancement with central hypointensity was noted on the gadolinium-enhanced images. Gadolinium-enhanced T1-weighted and unenhanced T2-weighted MR images showed significantly higher CNRs than unenhanced T1-weighted MR images. Residual tumor was detected after RF thermal ablation in two cases and was best seen on unenhanced T2-weighted and gadolinium-enhanced T1-weighted MR images. CONCLUSION: After initially increasing in size within the first 2 weeks, renal RF thermal ablation zones involuted during the remainder of the MR imaging follow-up period.

Adult↗
PubMed2005

Remnants of fetal circulation: appearance on MDCT in adults.

OBJECTIVE: The objective of our study was to describe the appearance of the remnants of the fetal circulation in adults on MDCT. CONCLUSION: The use of MDCT allows frequent visualization of the remnants of the umbilical vein, ductus venosus, foramen ovale, ductus arteriosus, and umbilical arteries.

Adult↗
PubMed2004

Assessment of parallel acquisition techniques in adrenal magnetic resonance imaging: does increased temporal resolution significantly improve visualization of adrenal lesions?

RATIONALE AND OBJECTIVES: To compare conventional radiofrequency coil reception techniques with parallel coil array acquisition methods in adrenal tissue visualization and to evaluate the dependence of temporal resolution on image quality in adrenal magnetic resonance magnetic resonance (MR) imaging. MATERIAL AND METHODS: Using a 1.5 T MR imager, conventional and parallel sampled sequences were acquired in 10 healthy volunteers and 10 patients with adrenal lesions. The imaging protocol consisted of: conventional (TR/TE 4,730/125 ms; FA 150 degrees; NA 1; AT 25 s), and two parallel imaging SMASH techniques (TR/TE 4,090/125 ms; FA 150 degrees; NA 1 resulting in an AT of 12 s, as well as NA 2 resulting in an AT of 24 s) with generalized autocalibration T(2)-weighted turbo spin echo sequences with 5 mm slice thickness, 1.6 mm in-plane resolution, and an acceleration factor 2. Severity of breathing motion and aliasing artifact and overall image quality were rated on five-point scales and evaluated with student's t test; a differential receiver operating characteristic (DROC) analysis was performed. RESULTS: Adrenal gland findings included adenomas, metastases, and hemorrhages. Acceleration of conventional turbo spin echo sequence with one signal average led to an increase in diagnostic power (DROC 0.362) as well as significant improvement in overall image quality (P(Volunteers) =.017; P(Patients) =.042) and reduction of breathing motion artifact in patients (P(Patients) =.012) while improving the temporal resolution. Parallel imaging with two signal averages resulted in further improvement of image quality over conventional imaging (DROC 0.303), (P(Volunteers) =.045; P(Patients) =.022), in the same acquisition time as the conventional method. CONCLUSION: Parallel acceleration of sequences used for adrenal tissue visualization leads to a significant increase in diagnostic quality by significantly reducing breathing motion artifacts without sacrificing contrast indispensable for adrenal lesion characterization.

Adenoma↗
PubMed2004

Comparison of MR imaging sequences for liver and head and neck interventions: is there a single optimal sequence for all purposes?

RATIONALE AND OBJECTIVES: To compare the appropriate pulse sequences for interventional device guidance during magnetic resonance (MR) imaging at 0.2 T and to evaluate the dependence of sequence selection on the anatomic region of the procedure. MATERIALS AND METHODS: Using a C-arm 0.2 T system, four interventional MR sequences were applied in 23 liver cases and during MR-guided neck interventions in 13 patients. The imaging protocol consisted of: multislice turbo spin echo (TSE) T2w, sequential-slice fast imaging with steady precession (FISP), a time-reversed version of FISP (PSIF), and FISP with balanced gradients in all spatial directions (True-FISP) sequences. Vessel conspicuity was rated and contrast-to-noise ratio (CNR) was calculated for each sequence and a differential receiver operating characteristic was performed. RESULTS: Liver findings were detected in 96% using the TSE sequence. PSIF, FISP, and True-FISP imaging showed lesions in 91%, 61%, and 65%, respectively. The TSE sequence offered the best CNR, followed by PSIF imaging. Differential receiver operating characteristic analysis also rated TSE and PSIF to be the superior sequences. Lesions in the head and neck were detected in all cases by TSE and FISP, in 92% using True-FISP, and in 84% using PSIF. True-FISP offered the best CNR, followed by TSE imaging. Vessels appeared bright on FISP and True-FISP imaging and dark on the other sequences. CONCLUSION: In interventional MR imaging, no single sequence fits all purposes. Image guidance for interventional MR during liver procedures is best achieved by PSIF or TSE, whereas biopsies in the head and neck are best performed using FISP or True-FISP sequences.

Adult↗
PubMed2004

Comparison of ECG-gated rectilinear vs. real-time radial K-space sampling schemes in cine True-FISP cardiac MRI.

PURPOSE: To compare three k-space sampling schemes in cine True-FISP cardiac magnetic resonance imaging and to evaluate changes in calculated quantitative functional cardiac parameters as a function of underlying k-space sampling techniques. MATERIAL AND METHODS: Using a 1.5 T MR imaging system (Magnetom Sonata, Siemens Medical Solutions, Erlangen, Germany), three k-space data-sampling schemes: rectilinear (2.96 ms/1.58 ms/70 degrees /12 s TR/TE/FA/AcquisitionTime), and two radial k-space acquisitions, with filtered back-projection (RADIAL) (2.45 ms/1.25 ms/ 50 degrees /3.3 s TR/TE/FA/AT), and steady-state projection imaging with dynamic echotrain readout (SPIDER) (3.39 ms/1.62 ms/55 degrees /1.8 s TR/TE/FA/AT) of a True-FISP sequence were applied in 10 healthy volunteers. Long- and short-axis breath-hold series were acquired and signal-to-noise ratios (SNR) for blood and myocardium were determined, as was contrast-to-noise ratios (CNR). Quantitative cardiac functional analysis included: determination of end-systolic/end-diastolic volumes, ejection fraction, and left ventricular mass. Functional analysis was performed by two independent readers three times for each volunteer and k-space sampling strategy. Statistical analysis evaluated the accuracy of the measurements obtained from each of the three sampling techniques and the intra- and interobserver reliability. RESULTS: Intraobserver and interobserver reliability measures of functional data were homogeneous without statistically significant differences. Intraobserver correlation coefficients ranged from 0.94-0.99; interobserver correlation coefficients ranged from 0.97-0.99. Direct comparison of SPIDER- and RADIAL-sampled True-FISP sequences showed no statistically significant differences in measured functional parameters with interstudy correlation coefficients from 0.88-0.98. RADIAL and SPIDER images had better temporal resolution and were qualitatively judged to provide superior wall/blood border definition. Statistically significant differences were identified in each volumetric functional parameter when results from the rectilinear sampling acquisitions were compared with either radial or SPIDER sampling techniques. RADIAL and SPIDER results were consistently higher than volumetric measures obtained from the rectilinear data set. CONCLUSION: Employing faster sampling schemes led to enhanced signal homogeneity while maintaining the necessary CNR for estimation of functional cardiac parameters. Enhanced signal homogeneity and maintained CNR will most likely improve the accuracy of the cardiac functional parameter determination.

Adult↗