Joerg Barkhausen

Hydro-MRI of the Small Bowel: Effect of Contrast Volume, Timing of Contrast Administration, and Data Acquisition on Bowel Distention

OBJECTIVE The purpose of this study was to assess oral contrast agents, volumes of the agents, and time points of data acquisition in regard to small-bowel distention and patient acceptance. SUBJECTS AND METHODS Six healthy volunteers underwent imaging on 16 different days. Four volumes (450, 900, 1,350, and 1,800 mL) of each of the four contrast compounds (0.2% locust bean gum plus 2.5% mannitol, VoLumen containing 2.0% sorbitol, VoLumen containing 1.4% sorbitol, and tap water) were used. Two-dimensional true fast imaging with steady-state free precession data sets were acquired at 5-minute intervals after contrast ingestion. Distention values for small-bowel segments (duodenum, proximal and distal jejunum, ileum) and occurrence of side effects were documented. RESULTS Analysis of bowel distention revealed significantly greater distention for all carbohydrate sugar alcohol-containing solutions compared with water but no significant difference among the three contrast agents. Sufficient duodenal distention was achieved with 900 mL of any of the contrast agents, but imaging had to be performed soon after ingestion. For MRI of the distal jejunum and ileum, a volume of 1,350 mL is preferable, and the time point of data acquisition plays a minor role. Ingestion of 1,800 mL of the carbohydrate sugar alcohol solutions led to a significantly higher rate of side effects such as abdominal cramps than did ingestion of smaller volumes. CONCLUSION The data indicate that sufficient contrast consumption and optimal timing of data acquisition are essential to distention of the small bowel. Oral contrast agent protocols should be adapted to the bowel region in question.

Whole body positron emission tomography/computed tomography (PET/CT) tumour staging with integrated PET/CT colonography: technical feasibility and first experiences in patients with colorectal cancer

Aim: The aim of this study was to implement an imaging protocol for positron emission tomography/computed tomography (PET/CT) colonography and to combine this protocol with whole body PET/CT tumour staging for a single whole body examination for routine clinical use. Subjects and methods: A whole body PET/CT protocol for tumour staging and a protocol for PET/CT colonography were integrated into one examination. Fourteen prospective patients with suspected colorectal cancer underwent whole body PET/CT after aqueous bowel distension and pharmacological bowel relaxation. Colonoscopy and histopathology served as the standards of reference in all patients. Results: The modified PET/CT examination detected all but one lesion in the colon. One additional lesion was detected in a patient with incomplete colonoscopy due to high grade luminal stenosis. One polyp with malignant conversion was identified with the modified PET/CT protocol. PET/CT colonography proved accurate in local lymph node staging and staged nine out of 11 patients correctly. Six additional extracolonic tumour sites were detected based on the whole body staging approach. Conclusion: Whole body PET/CT with integrated colonography is technically feasible for whole body staging in patients with colorectal cancer. Based on these initial diagnostic experiences, this integrated protocol may be of substantial benefit in staging patients with colorectal cancer, focusing on patients with incomplete colonoscopy and those with small synchronous bowel lesions.

Magnetic resonance colonography without bowel cleansing: a prospective cross sectional study in a screening population

Background and aim: To evaluate the diagnostic accuracy of magnetic resonance colonography (MRC) without bowel cleansing in a screening population and compare the results to colonoscopy as a standard of reference. Methods: 315 screening patients, older than 50 years with a normal risk profile for colorectal cancer, were included in this study. For MRC, a tagging agent (5.0% Gastrografin, 1.0% barium sulphate, 0.2% locust bean gum) was ingested with each main meal within 2 days prior to MRC. No bowel cleansing was applied. For the magnetic resonance examination, a rectal water enema was administered. Data collection was based on contrast enhanced T1 weighted images and TrueFISP images. Magnetic resonance data were analysed for image quality and the presence of colorectal lesions. Conventional colonoscopy and histopathological samples served as reference. Results: In 4% of all colonic segments, magnetic resonance image quality was insufficient because of untagged faecal material. Adenomatous polyps >5 mm were detected by means of MRC, with a sensitivity of 83.0%. Overall specificity was 90.2% (false positive findings in 19 patients). However, only 16 of 153 lesions <5 mm and 9 of 127 hyperplastic polyps could be visualised on magnetic resonance images. Conclusions: Faecal tagging MRC is applicable for screening purposes. It provides good accuracy for the detection of relevant (ie, adenomatous) colorectal lesions >5 mm in a screening population. However, refinements to optimise image quality of faecal tagging are needed.

High‐resolution continuously acquired peripheral MR angiography featuring partial parallel imaging GRAPPA

Continuously‐moving‐table MRI, in contrast to traditional multistation techniques, potentially can improve the scan time efficiency of whole‐body applications and provide seamless images of an extended field of view (FOV). Contrast‐enhanced MR angiography (CE‐MRA) in particular requires high spatial resolution and at the same time has rigid scan time constraints due to the limited arterial contrast window. In this study a reconstruction method for continuously acquired 3D data sets during table movement was combined with a self‐calibrated partial parallel imaging algorithm (generalized autocalibrating partially parallel acquisitions (GRAPPA)). The method was applied to peripheral CE‐MRA and compared with a standard continuously‐moving‐table MRA protocol. The gain in scan time was used to increase the data acquisition matrix and decrease the slice thickness. The method was evaluated in five healthy volunteers and applied to one patient with peripheral arterial occlusive disease (PAOD). The protocols were intraindividually compared with respect to the signal‐to‐noise ratio (SNR) and contrast‐to‐noise ratio (CNR) in selected vessel segments, as well as overall vessel depiction. The combination of the continuously‐moving‐table technique with parallel imaging enabled the acquisition of seamless peripheral 3D MRA with increased resolution and an overall crisper appearance. Magn Reson Med, 2006.

Detection of coronary stenoses with contrast enhanced, three-dimensional free breathing coronary MR angiography using the gadolinium-based intravascular contrast agent gadocoletic acid (B-22956)

PURPOSE To determine the diagnostic value of the intravascular contrast agent gadocoletic acid (B-22956) in three-dimensional, free breathing coronary magnetic resonance angiography (MRA) for stenosis detection in patients with suspected or known coronary artery disease. METHODS Eighteen patients underwent three-dimensional, free breathing coronary MRA of the left and right coronary system before and after intravenous application of a single dose of gadocoletic acid (B-22956) using three different dose regimens (group A 0.050 mmol/kg; group B 0.075 mmol/kg; group C 0.100 mmol/kg). Precontrast scanning followed a coronary MRA standard non-contrast T2 preparation/turbo-gradient echo sequence (T2Prep); for postcontrast scanning an inversion-recovery gradient echo sequence was used (real-time navigator correction for both scans). In pre- and postcontrast scans quantitative analysis of coronary MRA data was performed to determine the number of visible side branches, vessel length and vessel sharpness of each of the three coronary arteries (LAD, LCX, RCA). The number of assessable coronary artery segments was determined to calculate sensitivity and specificity for detection of stenosis > or = 50% on a segment-to-segment basis (16-segment-model) in pre- and postcontrast scans with x-ray coronary angiography as the standard of reference. RESULTS Dose group B (0.075 mmol/kg) was preferable with regard to improvement of MR angiographic parameters: in postcontrast scans all MR angiographic parameters increased significantly except for the number of visible side branches of the left circumflex artery. In addition, assessability of coronary artery segments significantly improved postcontrast in this dose group (67 versus 88%, p < 0.01). Diagnostic performance (sensitivity, specificity, accuracy) was 83, 77 and 78% for precontrast and 86, 95 and 94% for postcontrast scans. CONCLUSIONS The use of gadocoletic acid (B-22956) results in an improvement of MR angiographic parameters, asssessability of coronary segments and detection of coronary stenoses > or = 50%.

CT-Guided Biopsy of Small Liver Lesions: Visibility, Artifacts, and Corresponding Diagnostic Accuracy

PurposeOur study aimed to determine the visibility of small liver lesions during CT-guided biopsy and to assess the influence of lesion visibility on biopsy results.Material and MethodsFifty patients underwent CT-guided core biopsy of small focal liver lesions (maximum diameter, 3 cm); 38 biopsies were performed using noncontrast CT, and the remaining 12 were contrast-enhanced. Visibility of all lesions was graded on a 4-point-scale (0 = not visible, 1 = poorly visible, 2 = sufficiently visible, 3 = excellently visible) before and during biopsy (with the needle placed adjacent to and within the target lesion).ResultsForty-three biopsies (86%) yielded diagnostic results, and seven biopsies were false-negative. In noncontrast biopsies, the rate of insufficiently visualized lesions (grades 0–1) increased significantly during the procedure, from 10.5% to 44.7%, due to needle artifacts. This resulted in more (17.6%) false-negative biopsy results compared to lesions with good visualization (4.8%), although this difference lacks statistical significance. Visualization impairment appeared more often with an intercostal or subcostal vs. an epigastric access and with a subcapsular vs. a central lesion location, respectively. With contrast-enhanced biopsy the visibility of hepatic lesions was only temporarily improved, with a risk of complete obscuration in the late phase.ConclusionIn conclusion, visibility of small liver lesions diminished significantly during CT-guided biopsy due to needle artifacts, with a fourfold increased rate of insufficiently visualized lesions and of false-negative histological results. Contrast enhancement did not reveal better results.

Whole-body magnetic resonance imaging featuring moving table continuous data acquisition with high-precision position feedback

A novel setup for whole‐body MR imaging with moving table continuous data acquisition has been developed and evaluated. The setup features a manually positioned moving table platform with integrated phased‐array surface radiofrequency coils. A high‐precision laser position sensor was integrated into the system to provide real‐time positional data that were used to compensate for nonlinear manual table translation. This setup enables continuous 2D and 3D whole‐body data acquisition during table movement with surface coil image quality. The concept has been successfully evaluated with whole‐body steady‐state free precession (TrueFISP) anatomic imaging in five healthy volunteers. Seamless coronal and sagittal slices of continually acquired whole‐body data during table movement were accurately reconstructed. The proposed strategy is potentially useful for a variety of applications, including whole‐body metastasis screening, whole‐body MR angiography, large field‐of‐view imaging in short bore systems, and for moving table applications during MR‐guided interventions. Magn Reson Med, 2005.

MR-guided core biopsy with MR fluoroscopy using a short, wide-bore 1.5-Tesla scanner: Feasibility and initial results

To evaluate MR fluoroscopy in a short, wide‐bore 1.5T MRI suitable for near real‐time biopsy guidance.

Reference Right Atrial Function Determined by Steady-State Free Precession Cardiovascular Magnetic Resonance

BACKGROUND There is agreement that measurements of atrial volumes and ejection fraction (EF) are superior to atrial diameters for accurate determination of atrial size, follow up studies and prognosis. However, reference values for right atrial volumes and EF for cardiovascular magnetic resonance (CMR) have not been established but are crucial to identify patients with impaired right atrial function. METHODS AND RESULTS Atrial function was studied in 70 healthy subjects (52+/-16 years, 38 male) with both the standard short axis method (SA) and the area-length method (AL) using steady-state free precession gradient-echo cine imaging (SSFP). Intraobserver, interobserver (n=70) and interstudy (n=10) variability was assessed for both methods. Maximal volumes, minimal volumes and EF for SA and AL were 101.0+/-30.2 mL, 50.3+/-19 mL and 47.2+/-8.3%, and 103.2+/-32.6 mL, 50.8+/-20.2 mL and 51.4+/-9.2%, respectively. Maximal volumes, minimal volumes and EF were higher with AL than with SA (mean difference: 2.2+/-4.6 mL, 3.5+/-3.5 mL and 2.8+/-2.8%, respectively). Atrial function measurements were not related to gender (p>or=0.387) and age (rho<or=0.16) with either method. Intraobserver, interobserver and interstudy variability for volumes and EF was lower for SA compared to AL, with narrower limits of agreement. Analysis was faster with AL than with SA (62+/-18 s versus 7+/-2 minutes). CONCLUSION Normal ranges for right atrial function vary significantly between methods. AL is faster, but less reproducible than SA. Appropriate reference ranges should be used to differentiate normal from abnormal right atrial function.

Safety Measurements for Heating of Instruments for Cardiovascular Interventions in Magnetic Particle Imaging (MPI) - First Experiences

Magnetic particle imaging (MPI) has emerged as a new imaging method with the potential of delivering images of high spatial and temporal resolutions and free of ionizing radiation. Recent studies demonstrated the feasibility of differentiation between signal-generating and non-signal-generating devices in Magnetic Particle Spectroscopy (MPS) and visualization of commercially available catheters and guide-wires in MPI itself. Thus, MPI seems to be a promising imaging tool for cardiovascular interventions. Several commercially available catheters and guide-wires were tested in this study regarding heating. Heating behavior was correlated to the spectra generated by the devices and measured by the MPI. The results indicate that each instrument should be tested separately due to the wide spectrum of measured temperature changes of signal-generating instruments, which is up to 85°C in contrast to non-signal-generating devices. Development of higher temperatures seems to be a limitation for the use of these devices in cardiovascular interventions.