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J A Malko

Publications and source records attributed to J A Malko.

30 records · Page 2Linked to original sources
PubMed1985

A count-based algorithm for attenuation-corrected volume determination using data from an external flood source.

We discuss the basic features of a count-based algorithm for attenuation-corrected volume determination, for use with planar gamma camera images. The attenuation correction is arrived at by combining the results of two 180 degrees opposed images with a transmission image obtained with an external flood source. A sample of the imaged radioactive volume is used to convert the attenuation-corrected count to an absolute volume. The algorithm is best suited to the measurement of small to medium-sized volumes of uniform activity, such as are encountered in cardiac blood-pool imaging.

Heart↗
PubMedDate not supplied

Direct hepatic tumor injection in rats: can it be used for analysis of MR imaging contrast agent?

With a recently described rat model technique for direct hepatic injection of tumor cells for imaging research, there were concerns that the injection itself might produce lesions detectable with magnetic resonance (MR) imaging, thereby producing false-positive results. To examine this possibility, the authors prospectively studied 14 Sprague-Dawley rats after direct hepatic injection of cells from a rat hepatoma cell line. The rats were imaged with a variety of pulse sequences before and after intravenous injection of the contrast agent manganese dipyridoxal diphosphate at a dose of 8 mumol/kg. No intrahepatic lesions could be detected with MR imaging during the first 6 days after direct hepatic injection of the tumor cells. Therefore, the direct injection technique should be accurate for evaluating various MR imaging sequences and contrast agents for early hepatic tumor detection.

Animals↗
PubMedDate not supplied

Are hepatic and muscle T2 values different at 0.5 and 1.5 Tesla?

In an effort to determine whether T2 values of liver and muscle change with increasing field strength, 144 abdominal MR examinations were retrospectively evaluated. These patients were evaluated with a dual echo T2-weighted spin-echo sequence. Eighty-two of the examinations were performed at 0.5 Tesla and 72 at 1.5 Tesla (T). Eleven of the patients were evaluated with both MR systems with the same sequences. T2 values were also obtained from a Fe NH4(SO4)2 12H2O phantom. The T2 values of liver decreased from 57.8 +/- 11.3 at 0.5 T to 43.7 +/- 8.3 at 1.5 T. The T2 values of muscle decreased from 44.2 +/- 9 at 0.5 T to 35.4 +/- 7.2 at 1.5 T. Patients who were examined on both systems also demonstrated a decrease in both liver and muscle T2 values. For concentrations in the range of hepatic T2's, the phantom demonstrated a decrease in T2 values from 0.5 to 1.5 T ranging from 20.3 to 23.4%. All the T2 changes were statistically significant (p less than .05). The findings suggest that T2 values may depend on field strength, or may vary due to other hardware-related differences.

Evaluation Studies as Topic↗
PubMedDate not supplied

Controlled eddy currents: applications to MR imaging.

We describe how the artifact caused by eddy currents generated in free standing copper coils may be controlled and used to advantage in magnetic resonance (MR) imaging. The eddy currents distort the excitation field of the MR imager in the vicinity of the coil; the coils may then be used to reduce the signal intensity of tissues adjacent to them. Two examples of how this signal reduction may be used to advantage are given. In one example a coil was used to eliminate an aliasing artifact by removing the signal from an unwanted object. In another example a coil was placed on the anterior abdominal wall of a subject, thereby reducing the high-intensity signal from subcutaneous fat and the resulting ghosting from respiratory motion.

Abdominal Muscles↗
PubMedDate not supplied

Flow-sensitive MR imaging of ventriculoperitoneal shunts: in vitro findings, clinical applications, and pitfalls.

To determine ventriculoperitoneal shunt patency during routine MR imaging of the head, 23 patients were studied with T1-weighted fast-field-echo scans. Without knowledge of the results of previous MR/CT studies or of the patients' clinical history, we reviewed the fast-field-echo studies and divided them according to those judged to have shunt flow (18) and those judged not to have flow (five). Fast-field-echo sequences showed high signal intensity, consistent with CSF flow and shunt patency in 17 medium-pressure systems and one high-pressure system. No signal was seen in five patients with high-pressure valve shunts. Combined clinical evaluation and MR/CT studies showed that three patients had probable shunt malfunction. One patient had true shunt malfunction; and although malfunction was thought to be present in two symptomatic patients, surgical revision showed the shunts to be patent. The possibility of temporary shunt obstruction is postulated to explain the clinical and MR findings in those two cases. The remaining two cases (9% of the patients) had no clinical evidence of shunt malfunction, and the MR findings probably reflected periodic CSF flow. One patient had an intracranial segment that was not connected and showed no flow on MR. No false-positive results (apparent flow in a nonfunctioning shunt) occurred. Using a standard medium-pressure shunt system, we constructed and imaged a phantom, which confirmed our clinical observations. T1-weighted fast-field-echo sequences may be useful in assessing patency of medium-pressure CSF shunt systems.

Cerebrospinal Fluid Shunts↗
PubMedDate not supplied

MR measurement of intracranial CSF volume in 41 elderly normal volunteers.

A noninvasive nonplanimetric MR protocol was used to measure the total intracranial CSF volume in 41 normal subjects, aged 60-84 years, who were intensively screened to eliminate CNS disease. The protocol entailed application of MR imaging data acquired with a spin-echo sequence in a single thick slice encompassing the head. The results show a strong correlation between increased intracranial CSF volume and increasing age, and a weaker correlation between increased intracranial CSF volume and increasing total intracranial volume. The possibility of employing a CSF volume measurement as a reflection of brain atrophy to help diagnose dementia is discussed.

Aged↗
PubMedDate not supplied

The bright intervertebral disk: an indirect sign of abnormal spinal bone marrow on T1-weighted MR images.

Two phantoms were constructed and imaged for the purpose of reproducing and understanding the relatively increased signal intensity of intervertebral disks on T1-weighted MR images in three patients with diffuse vertebral metastases. The first phantom simulated a normal spine and showed that the disks and vertebral bodies were of similar intensity. The second phantom simulated an abnormal spine and showed that the disks were brighter than the vertebrae. Prolonged relaxation times from the vertebral bodies as well as manipulation of the window width and level are the factors responsible for the presence of bright disks on T1-weighted images. Variations in the window width and level can accentuate the apparent increase in signal intensity from the disks but not reverse it. Although the presence of bright disks may be subtle, recognition of this sign should raise the possibility of diffuse replacement of normal fatty bone marrow in the vertebrae.

Aged↗
PubMedDate not supplied

The behavior of Pantopaque on MR: in vivo and in vitro analysis.

MR imaging is considered by many to be the procedure of choice in imaging the spinal cord; yet we encountered an important pitfall of this procedure in the form of a patient with retained intraspinal Pantopaque. The results of this case are presented as well as those obtained in another patient with retained Pantopaque. Also described is the behavior of this contrast material when using in vitro imaging data obtained from a CSF/Pantopaque phantom. When T1-weighted imaging sequences are used, Pantopaque gives a high signal and CSF gives a low signal. With long repetition time, (e.g., 4000 ms), the CSF signal is high and the Pantopaque signal is not. With repetition time around 1000 to 2000, both may be isointense. The implications of these findings are discussed.

Adult↗
PubMedDate not supplied

Gadolinium-DTPA and MR imaging of pituitary adenoma: a preliminary report.

Gadolinium-DTPA MR imaging (Gd-MR), unenhanced MR imaging, and contrast-enhanced CT studies were compared prospectively in six patients with surgically confirmed pituitary adenomas and three patients without sellar pathology to determine the utility of Gd-MR in the diagnosis of pituitary adenoma. In normal patients, the pituitary gland, cavernous sinus, and infundibulum enhanced by T1 shortening after gadolinium. In adenoma patients, two of four focal lesions identified with contrast-enhanced CT were identified with Gd-MR, and one was identified with unenhanced MR. The earliest short repetition-time sequence performed after gadolinium injection was best for focal lesion detection. Normal cavernous sinus enhancement by gadolinium made identification of cavernous sinus extension of adenoma difficult. Infundibulum displacement was better seen with contrast-enhanced CT (two vs one); however, unenhanced and Gd-MR were better than contrast-enhanced CT for demonstrating chiasmal compression (four vs three). Contrast-enhanced CT, Gd-MR, and plain MR were equally able to identify gland enlargement, sellar floor erosion, and abnormalities of the diaphragma sellae. In this preliminary series, we found Gd-MR to be promising for imaging adenomas; however, modifications in Gd-MR technique including thinner slices and immediate scanning after gadolinium injection are necessary for the best detection of focal lesions.

Adenoma↗
PubMedDate not supplied

A phantom study of intracranial CSF signal loss due to pulsatile motion.

MR imaging of the head often reveals localized areas of decreased signal intensity (flow voids) within the CSF. These flow voids are caused by turbulence within the CSF resulting from its pulsatile back-and-forth flow through the cerebral aqueduct and foramina. We describe a phantom that mimics the essential features of the CSF flow, and discuss its use in studying the dependence of the CSF flow void (CFV) on spin-echo (SE) and inversion-recovery pulse sequence parameters. The phantom had fluid-filled spaces to represent ventricles, and channels connecting these spaces to represent the aqueduct and foramina. A pump pushed the fluid in a pulsing manner through the phantom at various rates. The CFV was quantified by measuring signal loss relative to nonflowing fluid. The CFV did not appear to depend on repetition time or inversion time. The CFV was, however, strongly dependent on echo time (TE), and for single-echo SE sequences CFV became less severe as TE decreased. An even-echo rephasing effect was observed for multiecho sequences. Slice thickness and field of view also affected the appearance of the CFV, as did gating with respect to the pulsatile motion. These results imply that TE, field of view, slice thickness, and gating must be considered when using the appearance or absence of the CFV in diagnosis.

Cerebrospinal Fluid↗