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Biomedical subjects

R Maas

Publications and source records attributed to R Maas.

At least 109 records · Page 6Linked to original sources
PubMed1989

[MRT of extracranial hematomas at 1.5 T using spin echo and gradient echo sequences].

Magnetic resonance imaging (MRI) at 1.5 T was performed in 25 extracranial haematomas using spin-echo (SE) and fast-field-echo (FFE) sequences. The age of the haematomas was in 11 cases less than 2 days and in 9 cases more than 14 days. Fresh haematomas were isointense to skeletal muscle on T1-weighted SE images. With T2-weighted SE sequences, fresh haematomas had high signal intensity on the first day, but became inhomogeneous with predominantly low signal intensity on the following days. Areas of low signal intensity could be demonstrated by T2-weighted FFE sequences already on the first day after bleeding. Subacute haematomas were recognised by their high signal intensity on the T1-weighted SE images. Also with T2-weighted SE and FFE sequences, subacute haematomas showed increasingly high signal intensity. The characteristic appearance of haematomas facilitates their identification with MRI.

Hemarthrosis↗
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

[Contribution of endosonography to preoperative staging in esophageal and stomach cancer].

A total number of 113 patients with gastroesophageal cancer (47 esophageal cancer, 66 gastric cancer) were examined by endoscopic ultrasonography (EUS). The depth of tumor infiltration in the wall, involvement of lymph nodes and spread to adjacent organs were the features particularly stressed on. 61 patients (46 with gastric cancer, 15 with esophageal cancer) underwent radical resection thus enabling a comparative study with the histological findings. The accuracy rate of EUS in determining the depth of infiltration was 85% in esophageal cancers and 77% in gastric cancers. Regarding involvement of lymph nodes, EUS was accurate in 80% of esophageal cancers and in 87% of gastric cancers, whereas CT scan was accurate in 47% and 43% respectively. For detecting spread to adjacent organs EUS was also more accurate than CT scan.

Adenocarcinoma↗
PubMed1988

[NMR tomography of thoracic aortic dissection].

The results of magnetic resonance imaging in 10 patients with dissection of the thoracic aorta are presented. In 8 patients, the intimal flap was clearly contrasted from flowing blood in both lumina. In 2 patients the lack of phase shift of the intraluminal signal indicated complete thrombosis of the false lumen. Oblique sagittal sections parallel to the aortic arch and coronal sections through the ascending aorta demonstrated the extent of the dissection and provided information about the involvement of the origins of the coronary arteries and the branch vessels of the aortic arch. In 7 patients, the proximal site of communication between both lumina could be localized.

Aortic Dissection↗
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

[Segmentation of MR tomograms for quantitative volume estimation].

MR tomography yields better contrasts for soft tissues than other imaging methods. This allows a reliable measurement of the volume of brain structures, in particular for the ventricular system and e. g. structures in hydrocephalic states. Therefore a method is proposed for segmentation and volume estimation of MR tomograms that is implemented via a computer program. This method provides an accurate determination of the volume tested on multiple-slice-images of normal patients and a phantom. The substantial features and possibilities of this program usable for all kinds of structures in MR-tomograms are explained here in detail.

Cerebral Ventricles↗
PubMed1987

Quantitative electroelution of oligonucleotides and large DNA fragments from gels and purification by electrodialysis.

We have designed a new device [Biotrap (Elutrap in the U.S.A. and Canada), available from Schleicher & Schuell] for electroelution, -concentration , and -dialysis of DNA and other charged macromolecules above 5 kDa. In an electric field, the DNA migrates in an open channel out of the gel slice through a microporous membrane, BT2, into the trap section, where it is retained by a very dense, non-adsorbant, and inert membrane BT1. Specifically designed for use in an electric field, the matrix of this new membrane is much denser than that of dialysis membranes. In contrast to dialysis membranes, BT1 will not adsorb large DNA fragments nor allow passage of small DNA fragments when subjected to an electric field. In the absence of an electric field, BT1 and BT2 effectively seal the trap, maintaining the final elution volume of the purified sample. The trap can contain from 200-600 microliter and is collected from above with a pipet. In the experiments described here, 85-95% of oligonucleotides (14-mer) and large (150 kb) DNA fragments were recovered, independent of fragment length. The purity of the eluted DNA was demonstrated by restriction enzyme digestion, nick-translation, primer extension, end-labeling with polynucleotide kinase, and ligation. Electrodialysis was successfully used for the complete removal of common contaminants inhibiting the polynucleotide kinase reaction and for the removal of CsCl from DNA samples.

DNA↗
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

[Risks and artifacts in MRT (1.5 tesla) caused by metallic foreign bodies. Studies on phantoms and 60 patients].

Our experience of the effects of metallic foreign bodies on MRT high field examinations is described. In vitro measurements showed moderate magnetic torsion or displacement in a few cases. The findings in 60 patients with various metal foreign bodies and the resulting artifacts are discussed. Despite local loss of information, in the majority of cases there is additional evidence provided by MRT, which suffers less from foreign body artifacts than does CT. Stainless steel implants result in some signal loss and geometric distortion, but do not usually constitute a danger to the patient and do not affect the diagnostic information from surrounding structures.

Foreign Bodies↗
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↗
PubMed1987

Synthetic oligonucleotide probes complementary to rRNA for group- and species-specific detection of mycoplasmas.

A variety of genetic probes has been used for the detection of pathogenic bacteria. Here we present a straightforward approach for the development of group- and species-specific oligonucleotide probes complementary to mycoplasmal rRNA. These probes are useful not only for the identification of mycoplasmas in clinical specimens, but also for the detection of Mollicutes in contaminated cell cultures. Radiolabeled rDNA probes detected less than 1 x 10(3) organisms in an RNA-DNA hybridization procedure.

Cells, Cultured↗
PubMed1986

[Realtime sonography of intrascrotal space-occupying lesions].

In 848 examinations of the testes in 317 patients, including 253 follow-up and/or multiple follow-up examinations and 36 unilateral testicle examinations (e.g., orchidectomy, aplasia or nondescent) it was shown that sonography is a diagnostic method which is on the one hand capable of clearly differentiating cystic from solid space-occupying processes, and on the other hand also offers certain possibilities for evaluating the status of solid findings. Histologic identification of malignant tumors was only achieved with teratomas. The differential diagnostic problem was in differentiating scrotal tumors from focal orchitis, chronic epididymitis, testicular torsion and contusion, and in differentiation between paratesticular neoplasms and epididymitides. The testicular findings included testicular neoplasms, cicatrization and cysts of the tunic, sequelae of trauma, orchitis, cryptorchism, hypoplasia, aplasia, and testicular cysts. Paratesticular findings included hydroceles, spermatoceles, varicoceles, paratesticular neoplasms, epididymitides, paratesticular scars, and thickening of the testicular coat.

Diagnosis, Differential↗
PubMed1985

Cell transformation by the left terminal regions of the adenovirus 40 and 41 genomes.

To study the transforming capacity of the two fastidious adenoviruses 40 and 41 (Ad40 and Ad41), we have cloned the left terminal regions of their genomes. Transfection with plasmids containing these regions leads to transformation of primary baby rat kidney (BRK) cells. Cell lines derived from transformed cells show an intermediate transformed phenotype. The left terminal region was present in at least 50 copies in cells transformed by Ad41 and in 2-3 copies in Ad40-transformed cells. The integration patterns of the plasmids containing the left terminal region of Ad41 were similar in three different cell lines.

Adenoviruses, Human↗
PubMed1985

[Changes in the peripheral lymph nodes seen by ultrasonics].

Sonographic examinations of 1 416 patients performed between 1980 and 1983 with particular reference to the inguinal, axillary and neck regions have shown that it is quite possible to effect sonographic differentiation between enlarged lymph nodes with cicatricial indurations after non-specific inflammation on the one hand, and primary lymphomas or metastases of lymph nodes on the other. In many cases, it is also possible to differentiate between the enlargement of a total lymph node (acute inflammatory, primary malignant) and metastases in a lymph node. Positive findings in the soft parts were seen in 278 patients; of these, 175 were confirmed histologically and cytologically (via puncture with sonographic control). One finding was revealed as false positive. In 102 patients the sonographic finding was confirmed by means of lymphographies (n = 12), computed tomography (n = 27) or via the subsequent clinical course, proving the fact that it is also possible to detect sonographically the ability of lymphomas to respond to treatment with antibiotics, cytostatics, and radiation; the effects can be recognised and interpreted via changes of the echo patterns.

Biopsy, Needle↗