PubMed Health⌕ Search

Biomedical subjects

J H Langkowski

Publications and source records attributed to J H Langkowski.

17 recordsLinked to original sources
PubMed1994

Liver iron quantification: studies in aqueous iron solutions, iron overloaded rats, and patients with hereditary hemochromatosis.

For the noninvasive liver iron quantification by MRI in human iron overload diseases, fundamental proton relaxation mechanisms were studied in aqueous solutions with ferritin and other iron compounds, in experimentally iron overloaded rats, and in patients with iron overload diseases. MR-relaxation rates as a function of iron concentrations in the range of 0-7.5 mg Fe/g aqueous iron solutions, 0-5.4 mg Fe/g rat liver in vivo, and 0.16-4.9 mg Fe/g human liver in vivo were determined from multi- and sets of single-spin echo sequences (1.5 T imager). As predicted by theory, transverse relaxation rates (1/T2) in aqueous iron solutions, in liver tissue of rats, and in human liver tissue increased linearly with the iron concentration. A preliminary calibration for the liver iron quantification by MRI was performed from in vivo measurements of liver 1/T2-relaxation rates and liver iron quantification by atomic absorption spectroscopy in biopsies from 13 patients. With the single spin-echo method, precise in vivo liver iron quantification in humans also above 2.0 mg Fe/g liver tissue (T2 < 15 ms) should be accomplished on any imager with shortest spin-echo time available, at least TE < 20 ms.

Adult↗
PubMed1994

[Radiation-exposure studies of CT diagnosis with the standard and spiral technics].

Comparison of the radiation exposure during CT quoted in the literature shows considerable variation; this depends on differences in apparatus, methods of examination and measurements. A systematic investigation into radiation dose during CT is therefore necessary to obtain accurate radiation doses during various examinations in order to balance risks against usefulness. The present paper deals with the radiation dose received by the patient during examinations of the cerebrum, neck, thorax, upper and lower abdomen and pelvis, using standard and spiral CT techniques. Organ doses for all organs at risk, surface dose, total body dose and dose profiles along the body axis for each type of examination have been established, which will allow the user to evaluate radiation dose.

Female↗
PubMed1992

Noninvasive liver-iron quantification by computed tomography in iron-overloaded rats.

RATIONALE AND OBJECTIVES: The benefit of computed tomography (CT) for the noninvasive determination of liver-iron concentration in human iron-overload diseases is a controversy in the literature. To study the sensitivity of CT for liver-iron quantification under experimental conditions, the authors measured single- and dual-energy CT numbers in vivo in the livers of iron-overloaded rats. METHODS: Thirty-five rats were subjected to an iron-rich diet for various periods, from 1 to 20 weeks, then scanned by single- and dual-energy CT. CT absorption was correlated to liver-iron content, which was determined by wet ashing and spectrophotometry. RESULTS: Whereas a good correlation (r = 0.99 at 96 kV; r = 0.95 at 125 kV) between CT numbers and liver-iron concentration was found, CT was insensitive to low concentrations of iron. Dual-energy CT scanning results showed greater scattering in liver-iron quantification compared with single-energy CT. CONCLUSIONS: In rats, the sensitivity of single- and dual-energy CT is too low to quantify liver iron in the diagnostically most relevant region of mild liver siderosis (1-3 mg iron/g wet weight [w.wt]).

Animals↗
PubMed1990

[Magnetic resonance tomographic diagnosis of retrobulbar neuritis using inversion recovery sequences].

Inversion recovery sequences with short inversion periods (STIR sequences) are particularly suitable for the examination of the intra-orbital and intracanalicular portion of the optic nerve, since they selectively suppress interference from neighbouring fat. This technique makes possible direct demonstration of retrobulbar neuritis that had to be diagnosed exclusively by clinical criteria up to now. As evidence of inflammatory changes in 15 out of 18 patients with acute retrobulbar neuritis, there were areas of increased signal intensity in the affected nerve; in six cases the nerve was also swollen. In eight normals and five patients with healed retrobulbar neuritis, the signal and calibre of the optic nerves were normal.

Adult↗
PubMed1989

[Quantitative volumetric determinations on MR tomograms in communicating hydrocephalus].

For patients with communicating hydrocephalus the implantation of a cardioventricular shunt is mostly an approved therapy. However, indications are frequently problematic and therefore a shunt operation will not be always successful. The proof of periventricular oedemas in addition to clinical signs seems to be a criterion for an indication for implantation and for the selection of a special valve. With the aid of a newly developed computer programme volume estimation of the ventricular system and the periventricular oedemas has been effected for six patients on T2-weighted MR-tomograms (1.5 tesla). Quotients of the different volumes are correlated with cerebrospinal fluid (CSF) pressure obtained during shunt implantation or lumbar measurement. Distinct indications have been found for a correlation between the volume of the periventricular oedemas and the pressure measurements.

Brain Edema↗
PubMed1989

[Measurement of noise levels in MR tomography at 1.5 Tesla].

The noise levels at the isocentrum of an MR apparatus with a field strength of 1.5 Tesla was measured during various sequences. The rapid switching of the gradients exerts effects on the gradient coils, which result in the development of noise as from a loudspeaker. Measurements were carried out using gradients of 3 and 9.3 mT/m with head and body coils and a variety of sequences. The noise level depended largely on the type of sequence and, under extreme conditions, may attain 96 dB. Because of the short exposure times, we do not consider it necessary to use any form of protection. During the examination of patients with damaged hearing, some protection may be advisable.

Humans↗
PubMed1989

[Diagnostic strategy in liver and pancreatic tumors: imaging diagnosis using MRT].

Because of distinct motion artifacts MR examinations of the upper abdomen are not performed routinely. The development of rapid imaging methods (gradient echoes) makes it possible to obtain an MR image in a few seconds, hence breath-holding is possible. Consequently, images can be obtained without respiratory artifacts. Experiences with 73 patients with liver lesions are reported, using gradient echoes. The MR investigations included T2 weighted images, T1 weighted without and with contrast agent (Gd-DTPA). MR of the liver can differentiate between metastasis and haemangiomas and can help in difficult cases before resection of liver metastases. Development and improvements of artifact-reducing methods, shortening of examination times and development of oral contrast agents and further intravenous contrast agents will extend the range of MR examinations of the upper abdomen.

Carcinoma, Hepatocellular↗
PubMed1988

[Magnetic resonance tomography of the feet and ankle joints].

21 patients with suspected, or known, abnormalities of the feet or ankles were examined by magnetic resonance tomography. The indications were: osteochondritis dissecans of the talus (three cases), osteomyelitis (three cases), suspected tumour recurrence (three cases), undiagnosed pain (six cases) and a further miscellaneous six cases. Although most of these problems could have been solved with other imaging methods, magnetic resonance tomography did add some valuable diagnostic information. Because of its ability to demonstrate bones, synovia, tendons, vessels and subcutaneous fascia in a multi-directional manner, it is superior to all other imaging methods. It saves time by making it unnecessary to use a variety of diagnostic procedures.

Adolescent↗
PubMed1988

[CT morphology of malignant schwannoma].

Thirty patients with histologically confirmed malignant schwannomas were examined. In five patients the lesions were malignant neurofibromas, as part of von Recklinghausen's disease, the others were solitary malignant schwannomas. CT appearances of malignant schwannomas are variable. Shape, structure and attenuation vary considerably. Most malignant schwannomas present with the CT criteria of benign tumours. Altogether neither the solitary schwannomas, nor those associated with von Recklinghausen's disease show specific diagnostic features, whether for the primary tumour or for recurrences. Reliable information on the nature of these lesions is possible in a few cases only.

Adult↗
PubMed1988

[Dacryocystography--conventional technic or digital subtraction technic?].

The lacrimal drainage systems of 92 patients were examined by a digital subtraction technique; 30 patients were examined additionally by a conventional technique, using films obtained during screening for the contrast injection. The digital subtraction dacryocystogram provided excellent demonstration of the lacrymal sac and of the tear ducts, but there is little diagnostic gain when compared with the conventional technique. Both methods are highly reliable. In view of its low radiation dose and rapid and simple course, conventional dacryocystography is regarded as the method of choice for routine examinations. The digital subtraction technique should be reserved for special problems.

Adolescent↗
PubMed1987

[Pulse triggering in magnetic resonance tomography in high-field strength].

Gated images of patients with stronger pulsation artefacts in the brain stem were produced on a 1.5 tesla MR-imager, registering blood pulsations by means of a finger plethysmograph. A minimization of movement artefacts was achieved and thus sufficient diagnostic-value of images in these patients was noticeable. This gating method seems to be a promising simple alternative compared to the well known cardiac gating for imaging of the head and neck area. Its advantages and limitations are demonstrated.

Brain Stem↗
PubMed1987

[Methodologic variants on rapid MR imaging of the liver].

The development of rapid imaging methods makes it possible to obtain T1 and T2-weighted MR images in less than 15 seconds. Consequently images can be obtained without respiratory artefacts. An attempt has been made to obtain optimal factors for the fast-field-echo procedure in order to obtain satisfactory images of the liver with T1 and T2 sequences. By moving the examination couch, it is possible to obtain 10 mm transverse sections without gaps throughout the entire liver in a reasonable time. The additional use of contrast medium (Gd-DTPA) provides information about perfusion and leads to an increase in contrast between lesions and normal liver tissue with adequate image quality. The method is particularly valuable before surgery for liver metastases.

Contrast Media↗
PubMedDate not supplied

Pre-operative localized in vivo proton spectroscopy in cerebral tumors at 4.0 Tesla--first results.

Sixteen patients with prediagnosed cerebral lesions were studied with stimulated echo localized 1H-spectroscopy at 4 Tesla. Initially, CT cerebral angiography and MR investigation at 1.5 Tesla were performed. After selecting a patient and receiving his agreement the high field examination started with the acquisition of an MR image of the known tumor at 4 Tesla using head or surface coil. 1H-spectroscopy was performed by selectively exciting a cubic volume between 8 to 20 cubic centimeters in the center of the tumor, in one case below 4 ccm (pinealoma). If possible, in a second examination the corresponding opposite side of the brain was studied. The extirpation of the tumor followed during the next days. Macroscopic aspects, histology and grading of the investigated lesions were determined. In some cases, specimens of the tumors were cooled in cooking salt solution and in liquid nitrogen, respectively, in order to perform in vitro proton MRS at 8.4 Tesla. The evaluable in vivo spectra showed good resolution and significant differences between corresponding cerebral areas with and without tumor as well as between different types of tumor histologies like medulloblastoma, astrocytoma and meningeomas. Often a good correspondence between in vivo and in vitro spectroscopy was seen. No clinically relevant side effects or complications were observed during the in vivo high field examination.

Adult↗