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K Hittmair

Publications and source records attributed to K Hittmair.

28 records · Page 2Linked to original sources
PubMed1995

Vegetable oil as an MR contrast agent for rectal applications.

The purpose of this study was to evaluate the feasibility of pure vegetable oil as an MR contrast agent for rectal applications. The hypothesis was that vegetable oil highlights the lumen of the rectum after rectal application as a positive contrast medium and offers additional contrast qualities using fat suppression techniques. Eleven MRI examinations were performed on 11 subjects (five healthy volunteers, all males, mean age 35 yr; and six patients, three males, three females, mean age 49 yr). Peanut oil, 200 ml, was applied rectally. In addition, 0.1 mmol/kg GD-DTPA was administered intravenously to the six patients only. Conventional T1-weighted SE sequences and T1-weighted SE images with fat suppression were obtained. Criteria for image evaluation were: overall image quality; uniformity of contrast distribution; chemical shift artifact; and delineation of the rectal wall. Side effects were assessed. There were no complaints reported by the 11 subjects. The image quality was sufficient in all studies. In all five of the volunteers and five of the six patients, the distribution of oil was uniform. Chemical shift artifacts did not deteriorate image quality. After rectal application of vegetable oil, the delineation of the rectal wall was sufficient with and without fat suppression techniques. Vegetable oil highlights the lumen of the rectum in MRI studies and offers additional contrast qualities with fat suppression techniques, acting as a positive as well as a negative contrast agent, depending on the chosen sequence.

Administration, Rectal↗
PubMed1995

Evaluation of solitary pulmonary nodules with dynamic contrast-enhanced MR imaging--a promising technique.

The evaluation of a solitary pulmonary nodule (SPN) is one of the most frequently encountered challenges in thoracic radiology. In addition to a "state-of-the-art" evaluation of SPNs with CT and biopsy techniques, recently the assessment of the enhancement characteristics with iodinized contrast agents has shown its potential to improve the characterization of SPNs. We investigated whether dynamic contrast-enhanced MRI is suitable to assess the degree and kinetics of MR contrast enhancement and whether this technique could help in the noninvasive specification of SPNs. We studied prospectively 21 patients with SPNs. T1-weighted and proton density-weighted spoiled gradient-echo breath-hold images (2D-FLASH) were obtained before and after the administration of Gd-DTPA in a standard dosage of 0.1 mmol/kg body weight. The maximum enhancement and the initial velocity of contrast uptake were assessed and correlated with pathohistological findings. To quantify contrast enhancement, we used the relative signal intensity increase (S(rel)) and the recently introduced enhancement factor (EF) and contrast uptake equivalent (CE). Dynamic contrast-enhanced MRI proved to be well suited for the assessment of the contrast enhancement characteristics of SPNs. Significant differences were found in the degree and kinetics of contrast enhancement for specific types of nodules. Malignant neoplastic SPNs enhanced stronger and faster than benign neoplastic SPNs. The strongest and fastest enhancement, however, was found in a benign type of nodules where histology revealed inflammatory/fibrous lesions. These differences in contrast enhancement between the different pathohistological groups were more significant when EF and CE rather than S(rel) was used for the quantification of contrast enhancement. The results of this study indicate a potential role for dynamic contrast-enhanced MRI in the preoperative noninvasive evaluation of SPNs using EF and CE as contrast uptake assessment parameters.

Contrast Media↗
PubMed1994

[Magnetic resonance imaging of breast implants. Significance compared to mammography and ultrasonography].

Magnetic resonance imaging (MRI), mammography and ultrasonography were performed in 44 consecutive women (mean age 45 [29-70] years) with a total of 73 silicone breast implants. The implant had been inserted after mastectomy for cancer in 15 patients, for cosmetic breast augmentation in 29. MRI proved to be superior to the other two imaging modalities with respect to assessing implant content, capsule and surrounding tissues. In 39 patients MRI clearly demarcated the implant from the residual breast tissue. But in four patients the lateral MRI assessment was impaired by phase artefact and in one other by movement artefacts in a restless patient. Implant thickness was underestimated by mammography and ultrasonography compared with MRI. In nine cases mammography showed retromammary parenchyma, while MRI did so in 20. The posterior wall of the implant was visualized by mammography in only one patient, but in all of them by MRI. Ultrasonography failed in all patients to show the entire implant circumference. In three cases MRI was the only imaging method which revealed a defect in the implant capsule with extrusion of silicone.

Adult↗
PubMed1994

Method for the quantitative assessment of contrast agent uptake in dynamic contrast-enhanced MRI.

In previous papers relative signal intensity increase was used as a quantitative assessment parameter for contrast uptake in contrast-enhanced MRI. However, relative signal intensity increase does not only reflect contrast uptake but depends also on tissue parameters (native T1 relaxation time) and sequence parameters (repetition time and flip angle); thus, the contrast uptake cannot be assessed accurately using relative signal intensity increase. Based on an analysis of the contrast behavior of spoiled gradient echo sequences, a method is described in this paper that overcomes the limitations of relative signal intensity increase measurement. A parameter, called "enhancement factor" (EF) is introduced that approximates differential T1 relaxation rate. The enhancement factor scales linearly with contrast uptake and is independent of tissue and sequence parameters. The additional measurement time involved in determining the enhancement factor is less than 1 min and computation is straightforward. The practicality of the new method was confirmed by phantom measurements using T1-weighted and proton density-weighted spoiled gradient echo sequences (FLASH-2D). Enhancing tissues were simulated by water phantoms doped with increasing concentrations of Gd-DTPA.

Algorithms↗
PubMed1994

MR assessment of brain maturation: comparison of sequences.

PURPOSE: To evaluate the role of short-inversion-time inversion-recovery (STIR) sequences in assessment of brain maturation. METHODS: Twenty-seven infants and young children with normal neurologic development were examined by 1.5-T MR using a circularly polarized head coil. Axial T1-weighted and T2-weighted and spin-echo and STIR images were obtained. Signal intensity of different anatomic structures at individual sequences was classified relatively to reference sites and temporal sequence of signal intensity was observed. RESULTS: Signal intensity changes on T1-weighted and T2-weighted spin-echo sequences occurred at ages described in various previous publications. On STIR images intensity changes became apparent at a time between T1-weighted and T2-weighted images. The advantages of the STIR sequence were improved assessment of myelination of subcortical cerebral white matter from 6 to 14 months and good contrast between white matter lesions and cerebrospinal fluid. CONCLUSION: Our results suggest that from 0 to 6 months myelination can be assessed best using a combination of T1-weighted and T2-weighted images; from 6 to 14 months a combination of T2-weighted and STIR images seems to be advantageous; after 14 months the use of only T2-weighted sequences is sufficient. After 14 months STIR images may be useful in detecting small periventricular white matter lesions or in cases with retarded myelination and isointensity between gray matter and white matter.

Brain↗
PubMedDate not supplied

Mathematical analysis of arterial enhancement and optimization of bolus geometry for CT angiography using the discrete fourier transform.

PURPOSE: The goal of this work was to develop a clinically applicable mathematical algorithm to analyze and optimize individual arterial enhancement in CT angiography (CTA). METHOD: Assuming a time-invariant linear system, the discrete Fourier transform was used to calculate the transfer function of the system ("patient function") from the arterial time-attenuation response to a test bolus. The patient function was subsequently used to predict aortic enhancement in five select patients and to calculate optimized biphasic injection protocols in two of these patients undergoing CTA of the abdominal aorta. RESULTS: Arterial time-attenuation curves were accurately predicted in all patients. Optimized biphasic contrast agent injection protocols resulted in uniform aortic enhancement at the predefined level over the entire scanning period in both subjects despite markedly different contrast agent volumes and injection rates used. CONCLUSION: Fourier analysis of the time-attenuation response to a test bolus is a simple and feasible approach to optimize arterial enhancement in CTA.

Angiography↗
PubMedDate not supplied

Accuracy of predicting and controlling time-dependent aortic enhancement from a test bolus injection.

PURPOSE: The purpose of this work was to determine the accuracy of predicting arterial enhancement from peripheral versus central venous test bolus injections at CT angiography (CTA). METHOD: In 40 patients with abdominal aortic aneurysms, aortoiliac enhancement profiles were predicted by mathematical deconvolution of the time-attenuation response to a 16 ml test bolus injection. Injection sites were either a cubital vein (n = 20) or a central venous injection site (n = 20). The accuracy of predicting enhancement was quantified as the "off-predicted deviation" (calculated as mean squared differences between observed minus predicted enhancement values) in all patients. RESULTS: Off-predicted deviation was significantly smaller in the central venous injection group (17 +/- 6 HU) than the peripheral injection group (33 +/- 18 HU) (p < 0.001). CONCLUSION: Arterial enhancement at CTA can be mathematically predicted and controlled more accurately if a central venous injection site is used. Automated saline flushing of the veins might improve the accuracy of the mathematical model for peripheral injections.

Aged↗