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Biomedical subjects

V M Runge

Publications and source records attributed to V M Runge.

At least 91 records · Page 5Linked to original sources
PubMed1988

Interactions of paramagnetic contrast agents and the spin echo pulse sequence.

The theoretical equations for paramagnetic contrast agent effects and the spin echo pulse sequence are combined to graph magnetic resonance (MR) intensity as a function of paramagnetic contrast agent concentration for various tissues. Analysis of the graphs and equations demonstrate several technical and clinical implications. These include: (1) positive enhancement is most likely to occur with short TEs and TRs; (2) changes in machine parameters TE and TR will change the concentration of agent at which the peak enhancing MR intensity will occur; (3) there is an absolute maximum MR intensity that can be reached with contrast enhancement; (4) the maximum MR intensity reached with enhancement is dependent on the tissues' T2 and, to a lesser degree, T1 relaxation times; (5) certain TE and TR combinations will cause no enhancement; (6) if positive enhancement does occur, it will usually occur only over a limited range of agent concentration; and (7) the tissues' T1 relaxation time but not its T2 time determines whether positive enhancement will occur and the relative amount of enhancement.

Contrast Media↗
PubMed1988

Physiology of the retrocalcaneal bursa.

To clarify the function of the retrocalcaneal bursa the hindfoot was studied by magnetic resonance imaging at various positions of the ankle joint. In normal individuals a tongue-like extension of the retromalleolar fat pad entered the bursa during plantar flexion as the angle between Achilles tendon and calcaneus widened. The reverse occurred in dorsiflexion. In contrast, in a patient with spondyloarthritis and retrocalcaneal bursitis excessive cavitary fluid prevented the intrusion of the fat pad. The sliding motion of the fat pad in and out of the bursa during ankle motion allows a more caudal, advantageous insertion of the Achilles tendon into the calcaneus.

Achilles Tendon↗
PubMed1988

Gd DTPA. Clinical efficacy.

Both the diagnostic accuracy and sensitivity of the MRI diagnosis of central nervous system neoplasms appear to be improved by the administration of a paramagnetic contrast agent, Gd DTPA.

Brain Neoplasms↗
PubMed1988

The straight and narrow path to good head and spine MRI.

The path to good head and spine images is narrow and treacherous. We have attempted to give the traveller a small but important set of basic rules, enabling him to cross with success. 1. Averaging can be used to achieve sufficient SNR for thin sections, but the cost in terms of scan time is high. Zooming the image (reducing the field of view) should generally be avoided, as the price in terms of SNR is very high. 2. Rectangular pixels and half-Fourier imaging are two methods for decreasing scan time. HFI, which produces high spatial resolution images, can be used when the SNR is not a limiting factor. Rectangular pixels improve the SNR, but decrease resolution. 3. To achieve good T1 contrast with spin echo imaging, set TE less than or equal to 20 msec. and TR less than or equal to 600 msec. For T2 weighted images, a TR between 2.0 and 3.0 sec. is preferred, typically with two echoes: for example, TEs of 25 and 90 msec. 4. Better slice profiles or gaps between slices can be used to combat slice-to-slice interference. This results in improved SNR on T1 weighted images and improved contrast on T2 weighted images. 5. Low bandwidth techniques may be used to improve the SNR on both T1 and T2 weighted images. Chemical shift artifact puts a finite limit on the extent to which this can be applied. 6. Motion compensating gradients are a tremendous boon to MRI and should be utilized in all possible head and spine applications. These reduce image degradation from CSF and vessel pulsation, as well as from involuntary motion. 7. Fast imaging techniques can be used in 2-D multislice mode to decrease scan time. Unfortunately the T2 contrast with this approach is far inferior to that of spin echo technique. 3-D FLASH, with 1 mm. sections, T1 contrast superior to spin echo technique, and the potential for high resolution reformatted images, may replace conventional 2-D, T1 weighted, spin echo imaging. Pulse techniques that combine all the advantages mentioned lie in the future. For example, one possible approach is a T2 weighted head screen that incorporates low bandwidth technique and HFI. This would produce high resolution images with reasonable SNR in approximately half the present scan time. Despite any further new developments, the trade-off between image quality and scan time will likely always remain.(ABSTRACT TRUNCATED AT 400 WORDS)

Head↗
PubMed1988

FLASH: clinical three-dimensional magnetic resonance imaging.

Using 3-D FLASH, high resolution, very thin section T1 weighted images of the CNS, spine, and extremities can be obtained. From these single data sets, reformatted images whose resolution is equal to that of the original data set can be constructed in any desired plane. This approach may lead to the replacement of conventional T1 weighted spin echo imaging by 3-D FLASH techniques.

Brain↗
PubMed1988

MR imaging of rat brain glioma: Gd-DTPA versus Gd-DOTA.

The enhancement properties of gadolinium diethylenetriaminepentaacetic acid (DTPA) and gadolinium tetraazacyclododecanetetraacetic acid (DOTA) were compared using a rat glioma model. In vitro analysis included the calculation of T1 relaxivity and determination of characteristic curves. Enhancement of the intracerebral glioma was studied in 23 rats approximately 2 weeks after glioma implantation with Gd-DTPA in 12 rats and Gd-DOTA in 11 rats. Six rats were also studied 1 week after implantation. Gd-DTPA exhibited a slightly greater T1 relaxivity in vitro than Gd-DOTA. Enhancement of the glioma was also greater with Gd-DTPA than with Gd-DOTA (P less than .05).

Animals↗
PubMed1988

MR imaging section profile optimization: improved contrast and detection of lesions.

A computer-optimized radio-frequency (RF) pulse for sharper section definition was implemented for T2-weighted magnetic resonance (MR) imaging of the head. Twenty-four patients underwent MR imaging with this technique and also with a conventional spin-echo technique with a sinc pulse filtered with a Hamming window. The contrast between gray and white matter improved 20%-40%, depending on the echo time. In ten patients with multiple sclerosis, use of the computer-optimized RF pulse resulted in detection of 37% more lesions, and power deposition was reduced by 36%. The computer-optimized RF pulse improved image contrast and lesion detection.

Brain↗
PubMed1988

Overcoming motion in abdominal MR imaging.

Anatomic structures that move periodically during the acquisition of data for an MR image become multiple ghosts in the phase-encoding direction. There is a constant spacing in pixels between consecutive ghosts, which is equal to the number of cycles of motion that occurred during the acquisition of data. The intensity of ghosts depends on the intensity of the moving structure and the number of pixels over which the motion occurred. No single method is completely satisfactory at suppressing motion artifacts. The major attributes and limitations of each method are summarized in Table 2, with plus (+) signs denoting merit. Theoretically, some methods perform better in reducing the intensity of ghosts and restoring the image intensity to its proper place. This certainly is not the final criterion, however. Some methods reduce the blurring in addition to suppressing the ghosts, or they suppress ghosts without prolonging the time for imaging. Certain methods also reduce ghosts from other kinds of motion. It is very appealing for a method to function without monitoring. The success of monitoring often depends too much on the cooperation of both the patient and technologist. The theoretical performance, attributes, and deficiencies of the various methods have been combined into a subjective overall rating in the last column of Table 2. All of the methods can be effective under the appropriate circumstances. Moreover, the methods are not mutually exclusive. It is advantageous, therefore, to combine methods to achieve even greater suppression. For example, physical restraint can be used for all but the most uncooperative patients. Most imaging techniques can be designed with gradients that rephase the signals from moving structures. Then other methods, such as averaging or reordering, can be applied as necessary. Fortunately, there are effective motion artifact suppression methods, even though not all are widely available yet on commercial equipment. Consistent suppression of motion artifacts will enhance the quality of MR images. Elimination of motion artifacts will improve the capability of MR to detect lesions and will provide a higher standard of performance for MR in the body.

Abdomen↗
PubMed1988

Magnetic resonance imaging with gadolinium-DTPA for detecting cardiac transplant rejection in rats.

To date, no noninvasive tool has gained widespread acceptance as an adequate substitute for endomyocardial biopsy for the diagnosis and grading of cardiac transplant rejection. We examined the potential role of magnetic resonance imaging with gadolinium (Gd)-diethylenetriamine penta-acetic acid (DTPA) image enhancement for the diagnosis of cardiac graft rejection. We studied 15 rats with heterotopic cardiac transplants, nine of which received no immunosuppression, and six of which received cyclosporine, azathioprine, and methylprednisolone. The animals underwent magnetic resonance imaging, which was immediately followed by sacrifice (2-12 days after transplant). Myocardial image enhancement was assessed on T1-weighted images performed before and after administration of Gd-DTPA, 0.5 mmol/kg. Histological specimens were graded I, II, or III to indicate increasing severity of rejection. In the absence of rejection, Gd-DTPA induced mild homogeneous myocardial enhancement. Ten of 11 cases with Grade II or III rejection manifested one or more areas of intense myocardial enhancement. The extent and distribution of intense myocardial enhancement corresponded to the severity and distribution of histological rejection. Quantitative myocardial enhancement, expressed as the ratio of maximal signal intensity after Gd-DTPA to signal intensity before Gd-DTPA administration, separated Grade I animals (1.61 +/- 0.27; mean +/- SD) from Grades II (2.89 +/- 0.58) and III (3.10 +/- 0.77; p less than 0.01) animals. In conclusion, cardiac transplant rejection is characterized by intense T1-weighted image enhancement after administration of Gd-DTPA. Magnetic resonance imaging with Gd-DTPA thus has potential application in the clinical diagnosis of cardiac transplant rejection.

Animals↗
PubMed1987

The efficacy of tilted axial MRI of the CNS.

The angle between the straight axial plane and the orbito-meatal line was measured in 156 consecutive magnetic resonance examinations. Inconsistent head positioning caused this angle to vary by as much as 44 degrees. Careful positioning of the patient by the technologist can minimize this variability, leading potentially to improved image interpretation. To assess the merit of a standardized orientation for MR examinations of the head, straight axial and tilted axial MR scans were compared in 34 patients. The tilted images were obtained parallel to the orbitomeatal line and were found to be superior for visualization of the cerebellum. When correlative x-ray CTs are available or when an abnormality in the posterior fossa is suspected, tilted axial MR scans should be employed.

Brain Diseases↗
PubMed1987

Optimization of spoiler gradients in FLASH MRI.

The FLASH technique for fast magnetic resonance (MR) imaging often employs strong magnetic field gradients, called spoiler gradients, to dephase the transverse magnetization after it has been measured. Otherwise, image artifacts can develop. The effectiveness of spoiler gradients at suppressing these artifacts was evaluated experimentally on two-dimensional MR images of a uniform phantom and patients. It was informative to compare the magnetization immediately before the RF excitation in each phase encoding step. Only spoiler gradients in the slice selection direction were effective. Spoiler gradients that decreased steadily from a large amplitude in the first phase encoding step to zero in the last minimized the transverse magnetization and suppressed the image artifact, without changing the image contrast.

Humans↗
PubMed1987

Chiari II malformation: MR imaging evaluation.

The purpose of this study was to explore the value of high-detail MR imaging in the diagnosis of the Chiari II malformation. Twenty-four patients with known Chiari II malformation as diagnosed by CT scanning were evaluated with cranial MR scans. Two patients also had spine scans. The sagittal-plane images were the most informative, and abnormalities of the telencephalon, diencephalon, mesencephalon, rhomboencephalon, upper spinal cord, and mesencephalon were shown extremely well. We found MR to be an easy and accurate method for demonstrating the abnormalities of the Chiari II malformation, and it is our procedure of choice.

Adolescent↗
PubMed1986

Primary glioma: diagnosis with magnetic resonance imaging.

Seventeen patients with surgically documented primary glial-origin brain tumors were evaluated by magnetic resonance imaging and high-resolution computed tomography. The exclusion of CT ring-enhancing lesions directed the focus of this study toward lower grade tumors that were more difficult to diagnose. The computed tomography abnormalities were often subtle and included areas of low attenuation, mass effect, and focal enhancement. Spin-echo sequences with both heavy T1 and T2 weighting were utilized. Prolonged T1 and T2 values were observed in all tumors. The T2-weighted spin-echo 1000/120 sequence was the most sensitive in tumor detection and was positive in all cases. Magnetic resonance imaging was superior to computed tomography in tumor detection, tumor localization, assessment of tumor extent, and determination of associated changes, ie, brain stem encroachment. All the magnetic resonance sequences used showed an increase in severity of imaging changes with increasing tumor grade. The T2-weighted sequence showed progressive margin irregularity, whereas the T1-weighted (inversion recovery) sequence showed increasing severity of internal tissue changes. The superior resolution of these changes by magnetic resonance imaging may have implications for better assessment of tumor grade in the future than is currently possible with computed tomography.

Adolescent↗
PubMed1985

Magnetic resonance imaging and other techniques in the diagnosis of multiple sclerosis.

We evaluated 35 patients with multiple sclerosis (MS) by magnetic resonance imaging (MRI), cerebrospinal fluid (CSF) analysis, evoked potential testing, and computed tomographic (CT) scanning. As classified by the McAlpine et al and McDonald and Halliday criteria, 27 patients had definite MS, three had probable MS, and five had possible MS. All of the patients had multiple white matter lesions detectable by MRI that were evident predominantly in the periventricular areas but also in the cerebral or cerebellar white matter. The severity of the MRI abnormality, as judged by the number and size of the lesions, correlated with the likelihood of a positive CT scan but not with the duration of disease, the degree of disability, or positive CSF oligoclonal banding. Magnetic resonance imaging successfully demonstrated brain-stem lesions in 15 patients (none were seen on CT scans). Magnetic resonance imaging seems to be a sensitive indicator of MS lesions, but clinical assessment will continue to be crucial to the diagnosis of MS.

Adult↗
PubMed1985

Particulate oral NMR contrast agents.

Insoluble paramagnetic compounds in suspension can be used to achieve visualization of the gastrointestinal system on magnetic resonance imaging (NMR). Particulate preparations of these agents decrease the T1 and T2 of solutions to which they are added. Gadolinium oxalate, a prototype of these particulate agents, was evaluated in vitro and in vivo (in rabbits) by NMR imaging. The effect of this compound upon T1 and T2 in vitro was also quantitated by NMR spectroscopy. Opacification of the upper gastrointestinal tract was achieved with gadolinium oxalate following oral administration. The colon was visualized following rectal administration.

Administration, Oral↗