Magnetic resonance-assisted imaging of slow flow in the pancreatic and common bile duct in healthy volunteers

BACKGROUND

Magnetic resonance cholangiopancreaticography (MRCP) is commonly used to evaluate the pancreatic (PD) and common bile duct (CBD), and the addition of secretin is used to obtain functional information (S-MRCP). Neither method gives any information on flow velocities within the ducts.

PURPOSE

To evaluate a new, MRI diffusion-based, slow-flow-sensitive sequence for the detection of slow flow changes in the PD and CBD.

MATERIAL AND METHODS

Seven healthy volunteers were examined. A modified single-shot turbo spin-echo sequence was used to detect slow flow changes. Three b factors (0, 6, and 12 s/mm(2)) were used. The flow sensitivity was applied in two directions, vertically and horizontally. Scanning was performed before and after glucagon was given, and again after an intravenous injection of secretin. The sequence gives signal loss from a duct when flow increases, and such changes were recorded.

RESULTS

All images showed the PD with b = 0 (no flow sensitization). After administration of glucagon, artifacts from bowel movements were reduced and visibility of the PD was improved at both b = 6 and b = 12. Significant reduction of the visibility of the PD, indicating increased flow, was recorded both at b = 6 and b = 12 after the administration of secretin. There were no changes in the visibility of the CBD.

CONCLUSION

This study shows that MRI-based detection of slow flow changes inside the PD is possible. Due to the sequence's high sensitivity to any motion, further studies are required before adopting the method for clinical use.

Dynamic first pass 3D EPI of the prostate: accuracy in tumor location

PURPOSE

To evaluate the potential of dynamic contrast enhanced (DCE) 3D EPI in the location of prostate cancer.

MATERIAL AND METHODS

A DCE 3D EPI scan was included in the magnetic resonance imaging protocol for prostate examination. Twenty-eight patients who subsequently underwent radical prostatectomy were included in the study. T2-weighted (T2W) Turbo Spin Echo (TSE) images were initially evaluated by two radiologists. Parametric images reflecting contrast enhancement were added and new evaluations performed. The results were compared with histology from resected specimens. Accuracies and interobserver agreements were calculated.

RESULTS

Interobserver agreement was Kw =49+/-3% for the T2W technique and Kw=30+/-3% for the combined techniques. No statistically significant advantages were found for location of tumor in the prostate or in the seminal vesicles by adding the DCE information.

CONCLUSION

DCE 3D EPI did not improve tumor location compared with that of T2W TSE images. Further investigation is needed on how best to exploit the DCE technique.

Bowel MR imaging with oral Gastrografin: an experimental study with healthy volunteers

Our objective was to evaluate Gastrografin for MR bowel imaging. Twenty-three healthy volunteers in two randomised groups received 300 or 400 ml 50% Gastrografin, drunk continuously during 2 and 3 h, respectively. Images were applied during breath-hold in three orthogonal orientations. The balanced fast-field echo (BFFE) and balanced turbo field-echo (BTFE) sequences, with acquisition times from 13 to 25 s, were used before gadolinium (Gd) DTPA implying 1- to 2-mm-thick slices locally or 6-mm-thick slices through the entire gastrointestinal tract. The Gd-enhanced images were performed using a 3D T1-weighted FFE sequence with water selective excitation (Proset). Image quality, including bowel distention, homogeneity of opacification and wall conspicuity, were evaluated by two experienced reviewers, and the adverse reactions were recorded. Very good or excellent distention, homogeneity and wall conspicuity were achieved in the central segments from the ileum to the left colon flexure in 83-96% of cases, due to the adequate contrast media supply in these regions. Distention, homogeneity and delineation were good in the central segments of the remaining bowels. Diarrhoea was a major problem affecting all participants, followed by nausea. Provided that there is modern fast sequential technology, excellent MR imaging of the bowel can be achieved by the oral administration 50% diluted Gastrografin. Further studies are needed to refine the technique and optimise the quantity and concentration of Gastrografin in order to avoid or reduce adverse reactions.

[Magnetic tomography--new imaging techniques and future perspectives]

BACKGROUND

From the very introduction of MRI into medicine, the modality has presented the user a long list of theoretical tissue contrast parameters. The development of MRI has been aimed at turning these theoretical possibilities into practical options.

MATERIAL AND METHODS

We give an overview of the new MRI techniques and perspectives for the future based on a literature search and our own experience.

RESULTS

Today, the modality offers state-of-the-art anatomical details as well as visualisation of several functional parameters such as perfusion, diffusion, blood oxygen saturation, and tissue temperature. In the near future, MRI may provide absolute quantification of regional perfusion and rate of oxygen consumption in a clinical setting. New vascular and gastrointestinal contrast media will further increase the sensitivity and specificity of MRI. A continuous increase in imaging speed has made MRI capable of providing adequate "fluoroscopic" guidance during interventional procedures, and real-time diagnostic imaging is only few years ahead.

INTERPRETATION

The spread of MRI installations will increase as a result of increasing demand for the best and least harmful diagnostic procedure. The main challenge to the MRI community will be to exploit the vast diagnostic possibilities.

[Magnetic resonance--historical and theoretical basis]

Magnetic resonance (MR) imaging is a fast developing modality that has become an indispensable diagnostic tool at numerous disease states. The first MR imager in Norway was installed in 1986; by the end of 1999 Norway will have a total of 39 units, approximately one unit per 114,000 inhabitants. MR technique uses radiowaves and magnetic fields, and no ionising radiation is involved. Imaging is based on the fact that all biological tissues are magnetized when placed in a strong, static magnetic field. Short radiofrequency pulses set the tissue magnetic vector into rotation, and the vector induces electric currents in a receiver coil. The electric signals are spatially encoded by means of magnetic field gradients, thus enabling image reconstruction by means of Fourier transformation. The signal intensities can be made dependent on several tissue parameters, thus creating several unique image contrast possibilities.

MR urography: the future gold standard in paediatric urogenital imaging?

BACKGROUND

Examination of the paediatric urogenital tract is traditionally performed using methods that utilise ionising radiation, such as intravenous urography (IVU), computerised tomography (CT), voiding cystourethrography (VCU), and scintigraphy, in addition to ultrasound (US).

OBJECTIVE

To determine the potential and effectiveness of MR urography (MRU) in infants and children. Materials and methods. 44 MRU examinations were prospectively performed in 39 patients (21 infants, mean age 3.5 months, and 18 children, mean age 6 years 2 months) with known or suspected pathology of the urinary tract. Non-enhanced, fast spin-echo sequences (TSE) were performed in all patients. In 70 % of the patients a contrast-enhanced, fast gradient-echo sequence (TFE) was included. The dynamic sequence was prolonged and supplemented with furosemide provocation in some patients with suspected urinary-tract obstruction.

RESULTS

Nine percent of examinations were non-diagnostic or interrupted due to movement. MRU contributed additional information in 66 %. Nine patients with suspected urinary-tract obstruction were examined with both contrast-enhanced MRU and scintigraphy. Three MRU examinations were less informative and one equal to scintigraphy when obstruction was the diagnosis. When using a technique with a prolonged dynamic sequence, including frusemide provocation, four MRU examinations were equal and one was superior to scintigraphy.

CONCLUSIONS

MRU has the potential to replace traditional diagnostic methods which use ionising radiation in paediatric patients. Further studies are needed before definite conclusions can be drawn.

Functional magnetic resonance imaging of primary visual processing using a 1.0 Tesla scanner

Recent advances in functional magnetic resonance imaging (fMRI) at > or = 1.5 T magnetic field strength and with high speed single-shot echo planar imaging techniques have made it possible to monitor local changes in cerebral blood volume, cerebral blood flow, and blood oxygenation level in response to sensory stimulation, simple motor activity, and possibly also to more complex cognitive processing. However, fMRI has also been accomplished on conventional MR scanners of medium field strength (approximately 1.0 T) using special pulse sequences and appropriate methods for image analysis. We present results from six subjects on photic stimulation using a standard 1.0 T MR scanner together with special software for off-line image analysis. Continuous serial T2-weighted imaging were performed for 6 minutes in the plane of the calcarine fissure. There were 3 repetitions of 1 minute resting state of darkness (OFF) and 1 minute activated state (ON) with 8 Hz flicker stimulation. To directly map these functional images to the underlying anatomy we also acquired a high resolution T1-weighted image from the same axial slice. The results demonstrated that stimulus-related signals can be obtained from primary visual cortex with a conventional 1.0 T MR scanner. Further methodological improvements are discussed and related to present and future possibilities for the use of fMRI within psychophysiology.