Determination of (40)ca(+) in the presence of (40)ar(+): an illustration of the utility of time-gated detection in pulsed glow discharge mass spectrometry.

The glow discharge ionization source operated in the pulsed, or modulated, power mode affords a number of distinct advantages over its steady-state counterpart. It is well-known that pulsed plasma operation permits the application of higher instantaneous powers by allowing time for the sample to cool. This minimizes sample overheating while effecting higher sputtering yields and lower limits of detection. The presence of discrete time regimes affords the added advantage of temporal selectivity. Such selectivity allows the observation of analyte ions during a time regime in which their signal is at a maximum while that of electron ionized background species is declining. Significantly, time regimes are found when no background argon ion signals are observable but analyte ion signals remain. This means that discrimination against isobaric interferences arising from the discharge gas is possible. A prime example of the utility of this advantage arises in the determination of calcium with an argon glow discharge. Both the major argon and calcium isotopes are found at a nominal m/z of 40. Time-gated mass spectrometeric detection during the afterpeak time regime enables the ready determination of (40)Ca(+) in samples at the ppm level. A linear calibration curve is obtained that also demonstrates the elimination of the (40)Ar(+) signal from mass spectra obtained with either a dc or rf glow discharge ion source.

MRI of fistula-in-ano: a comparison of endoanal coil with external phased array coil techniques.

PURPOSE: The objective of our study was to compare MRI of fistulas-in-ano using an endoanal coil with that using a pelvic phased array coil and to assess the value of a combined approach by correlating the findings with those at surgery. METHOD: Twenty consecutive patients with clinical suspicion of perianal sepsis were studied using an endoanal coil immediately followed by a phased array coil. T1 weighted and STIR images in transverse and coronal planes were made with each coil and analysed by noting the presence and site of a collection and primary track, the position of any internal opening, and subcutaneous or supralevator extension. Operative findings were similarly recorded. RESULTS: Of 20 patients with suspected fistulas, 8 had simple fistulas, 8 had complex fistulas, and 4 had no current evidence of infection. The concordance between MR and surgery for identifying the presence and site of the collection, the primary track, and the internal opening in both simple and complex cases was superior using the endoanal coil as compared with the phased array. Both coils together reflected the findings of the endoanal coil used alone. However, for supralevator/subcutaneous extension, concordance was superior using the phased array compared with the endoanal coil, and a combined approach reflected the values of the phased array coil used alone. CONCLUSION: Endoanal MRI is highly sensitive in the delineation of fistulas-in-ano. In combination with phased array techniques, it provides valuable preoperative assessment in both simple and complex cases.

Time-of-Flight Mass Spectrometry with a Pulsed Glow Discharge Ionization Source.

The pulsed glow discharge (GD) plasma source exhibits several characteristics that make it ideally suited for use with time-of-flight mass spectrometry (TOFMS). TOFMS uniquely affords the ability to monitor a narrow temporal window for a time-varying process such as ion formation in the pulsed glow discharge plasma. Pulsed GD-TOFMS exhibited distinct advantages for the direct determination of trace elements in solid state samples. Initially, the pulse-powered GD-TOFMS system used for these investigations exhibited poor resolution. In an effort to improve resolution, a slit was introduced to narrow the ion beam orthogonally entering the extraction region of the TOFMS. In an effort to determine optimal operating conditions, the influence of slit width on TOF performance was investigated. In the course of this study, the slit width was found to influence isotope ratio accuracy as well as resolution. A slit width of 1.0 mm was determined to provide the best compromise between resolution and isotope ratio accuracy. Pulsed GD-TOFMS affords improved sensitivity and selectivity because Penning ionization is enhanced during the time period immediately following the termination of the discharge power. Ions sampled by an extraction pulse applied after power termination also yield a mass spectrum that is free of contributions arising from electron-ionized interferences. This advantage arises because only ions generated via the Penning ionization mechanism persist after the termination of discharge power. Sampling in the "afterpeak" time regime eliminates the saturation of the detector arising from discharge support gas ion signal.

Magnetic resonance imaging of spinal cord in multiple sclerosis by fluid-attenuated inversion recovery.

Magnetic resonance imaging examination of the upper spinal cord was done in sixteen adult patients with clinically definite multiple sclerosis (MS) by T2 weighted fluid attenuated inversion recovery (FLAIR) scanning in which the signal from cerebrospinal fluid was suppressed. These scans were compared with matched images obtained with conventional T1 and T2 weighted pulse sequences (including contrast enhancement). 6 lesions (five patients) were seen with the conventional scans and 37 lesions (fourteen patients) were seen with the FLAIR scans. The FLAIR sequence considerably improves the ability of MRI to demonstrate spinal involvement in MS.

The MR contribution after CT demonstration of supratentorial mass effect without additional localising features.

The contribution of magnetic resonance (MR) imaging was retrospectively evaluated in 24 patients in whom CT demonstrated a supratentorial mass effect without significant additional localising features. Using a combination of T1-weighted inversion recovery (IR) and T2-weighted spin echo sequences, the MR images localised the lesion with greater precision than CT in 80% of cases. Areas of contrast enhancement were visible on the IR images in five of nine (56%) patients assessed after intravenous gadolinium-diethylenetriamine pentaacetic acid, where no comparable enhancement was seen on CT. Twenty of the 24 patients subsequently underwent surgery; eight had biopsies and 12 had resections. Magnetic resonance accurately predicted the site of the tumour in all these patients. Three of the remaining four cases were treated with radiotherapy on the basis of the MR findings without a tissue diagnosis being sought. Magnetic resonance produces better localization than CT and provides a sound basis for further diagnostic and therapeutic procedures.

Ultrasound, CT, and MRI comparison in primary and secondary tumors of the liver.

Thirty-five patients with surgically removed or percutaneous biopsy-proven tumors were examined by ultrasound, computed tomography (CT), and magnetic resonance imaging (MRI). This retrospective study describes the appearance of the primary tumors and metastases and compares the sensitivity and specificity of the 3 imaging methods. Ultrasound, CT, and MRI examinations as well as clinical, operative, and/or histologic data were available for all 35 patients. Paramagnetic contrast agent gadolinium-diethylenetriamine pentaacetic acid (Gd-DTPA) was used in 23 patients and a short TI inversion recovery MRI sequence was used in 23 patients, in addition to various spin echo MRI sequences. Thirteen patients were examined using both Gd-DTPA and the short TI inversion recovery sequence. Our comparative study--based on the following criteria: detection, size, location of the tumor, and portal vein involvement and bile duct dilatation--demonstrated an advantage of MRI over ultrasound in 16 of 35 cases, equal results in 17 of 35 cases and a disadvantage of MRI compared to ultrasound in 2 of 35 cases. With the identical criteria, MRI proved to be more informative than CT in 10 of 35 cases, equal in 21 of 35 cases, and less informative in 4 of 35 cases.

Magnetic resonance imaging of the solitary hepatic mass: direct correlation with pathology and computed tomography.

Magnetic resonance images (MRI) of the liver were obtained using a combination of short time inversion recovery (STIR) and spin echo (SE) sequences. These were correlated with comparable tissue slices generated from resected specimens obtained at partial hepatectomy. All 10 cases appeared to have solitary masses on contrast enhanced computed tomography (CT). Histological examination revealed five primary tumours (two hepatocellular carcinomas, two haemangiomas and one cholangiocarcinoma) and five metastatic tumours. The STIR images demonstrated a high signal intensity in all areas of viable tumour involvement and reduced signal intensity in regions of confluent necrosis with superimposed haemorrhage or calcification. This sequence also demonstrated additional areas of high signal intensity adjacent to several lesions which were not visible on CT. Microscopy of these regions in the specimens demonstrated no tumour involvement or steatosis and their precise cause remains obscure. All the lesions demonstrated on the CT images were visible on MRI and no additional lesions were discovered on detailed microscopical examination of the specimens. Delineation of the extent of the cholangiocarcinoma was a problem with both techniques. MRI showed no major advantage over CT except for a higher contrast of the lesion compared with normal liver and also a better delineation of the tumour mass.

Bone marrow in leukemia and aplastic anemia: MR imaging before, during, and after treatment.

Serial magnetic resonance (MR) studies of the cervical bone marrow were performed in five patients undergoing bone marrow transplantation for chronic granulocytic leukemia and in four patients with aplastic anemia who were treated with antilymphocytic globulin. Findings were compared with those from a group of healthy volunteers. Chemical shift imaging techniques were used to exploit the presence of protons in fat and water in the red marrow. Characteristic changes were seen in aplastic anemia before treatment, but derivation of images representing fat and water fractions was necessary to distinguish leukemic marrow. Acute changes during the treatment of leukemia may reflect the effects of chemotherapy and radiation therapy, whereas changes in the chronic phase of both diseases may prove useful in predicting treatment outcome. MR studies are likely to be useful in the assessment and treatment of hematologic disorders.

MR imaging in progressive multifocal leukoencephalopathy.

The MR imaging appearance of progressive multifocal leukoencephalopathy is described in four cases that were confirmed by brain biopsy. Characteristic aspects are long T1 and long T2 lesions limited to white matter. At first the lesions are round or oval, then confluent and large. There is no mass effect. The involvement is most often asymmetric and distant from the periventricular region. The differential diagnosis includes other diseases affecting white matter: demyelination, infarction, infection, and tumors.

Magnetic resonance imaging of the retroperitoneum.

The results of magnetic resonance imaging (MRI) examinations in 50 patients with histological or clinical diagnoses of retroperitoneal disorders and 20 normal volunteers are presented. An increase in relaxation time (T1) was recognised in most pathological conditions except for four liposarcomas and one adrenal cortical neoplasm and one metastatic lesion of the same gland. Inversion recovery (IR) provided the best tissue contrast, enabling the detection of small lesions. Flow-dependent sequences and sagittal imaging planes were particularly helpful in the evaluation of aortic aneurysms. Ferric ammonium citrate used as an oral paramagnetic contrast agent and a short T1 inversion recovery sequence gave encouraging initial results in recognising bowel loops. Gadolinium-DTPA injected intravenously provided tumour enhancement, indicating vascular perfusion and demarcating tumour margins. An attempt to eliminate motion artefacts was carried out in 15 volunteers and six patients either by a new software system (respiratory ordered phase encoding) or by using short T1 inversion-recovery to suppress the high signal from fat. The same pulse sequence results were useful in demonstrating subcutaneous fistulous tracts by eliminating the adjacent fat. The actual role of MRI in the investigation of the retroperitoneum in view of current technical developments is discussed.

Contrast-enhanced magnetic resonance imaging of tumours of the central nervous system: a clinical review.

The clinical application of the intravascular paramagnetic contrast agent gadolinium-DTPA for magnetic resonance imaging (MRI) imaging of tumours of the central nervous system (CNS) has been assessed over the past 3 years. Various patterns of contrast enhancement were observed, and situations in MRI where the administration of contrast medium may be useful have been defined. These include lesions which are isointense with normal brain matter, the separation of tumour from surrounding oedema, evaluation of the degree of blood-brain barrier breakdown, delineation of tumours obscured by overlying calcification on computed tomography (CT) and in the investigation of lesions in anatomical areas where CT has known limitations (brain stem, cervical spine). Changes in relaxation times in normal and abnormal tissues following contrast medium, toxicity and dosage of gadolinium-DTPA, and MRI pulse sequence techniques are reviewed.

Periventricular leukomalacia: evaluation with MR imaging.

We reviewed 24 magnetic resonance (MR) images of 12 infants diagnosed as having periventricular leukomalacia based on ultrasound results. Abnormalities were identified on the MR images of every patient and were divided into three categories: distribution of low-signal-intensity areas within the cerebral white matter, degree of ventriculomegaly and brain atrophy, and extent of myelination. Follow-up examinations on six patients were also compared for significant changes. Abnormalities noted on MR images that most consistently related to poor outcome for the patient were low-signal-intensity lesions involving all four cerebral lobes, moderate to severe delays in myelination, lack of progression of myelination, and moderate to severe cortical atrophy. MR imaging was able to depict the extent and progression of myelination, and it may be used to continue follow-up of these patients beyond the time of fontanel closure.

Present and future clinical position of magnetic resonance imaging.

Following the appearance of the first clinical reports on magnetic resonance imaging (MRI) five years ago, stock is now taken of the clinical value of this new imaging technique and its future potential is assessed. Contrast and spatial resolution as well as specificity of CT and MRI are compared and the multiplicity of sequences, multiplanar facility, and flexibility of MRI over CT are analyzed. The dominant role of MRI over CT in the study of some disorders of the central nervous system is assessed and so are the limitations. In this context the usefulness of paramagnetic contrast media is also evaluated. The difficulties of body imaging are discussed. The solutions of overcoming cardiac and respiratory motions artifacts are evaluated and areas where MRI has already achieved a high level of clinical application are identified. Mention is made of additional information obtainable by MRI as, for example, sodium imaging, blood flow measurements, and the combination of imaging with spectroscopy. Possible future prospects are analyzed, for example, high-resolution imaging, alternative sequences to those commonly used in particular the short TI IR sequence (STIR), chemical shift imaging, and the possibility of utilizing susceptibility for imaging purposes. The problem of radiofrequency receiver coil design is approached and so is the choice of magnetic fields. The future relationship of MRI with established noninvasive techniques is stressed.

Gadolinium-DTPA in the assessment of liver tumours by magnetic resonance imaging.

The effect of gadolinium-DTPA (Gd-DTPA, Schering AG) as a magnetic resonance imaging (MRI) contrast agent was studied in 15 patients with liver tumours. A dose of 0.1 mmol/kg was used. An analysis of the time-course of enhancement, a comparison of four different pulse sequences, and a dose-comparison study were carried out with monitoring of haematological and biochemical parameters before and after injection of Gd-DTPA. Maximum enhancement, that is, increase in signal intensity, was noted on IR1400/400/13 between 10 and 20 min after injection while on SE580/40 and SE580/80 maximum enhancement was noted 30 min after injection. In some cases enhancement was noted up to 120 minutes after injection. SR1000/13f sequences showed very little enhancement. On comparison with contrast-enhanced X-ray computed tomography (CT), enhancement was greater on MRI in seven cases, equal in six and less in two, as assessed subjectively. Additional lesions were shown in one case using Gd-DTPA compared to precontrast enhanced MRI scans. However, no additional lesions were seen on contrast-enhanced MRI scans compared to contrast-enhanced CT scans. Gd-DTPA is capable of enhancing liver tumours on MRI and may have a place in the assessment of the operability of such lesions.