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Biomedical subjects

D D Stark

Publications and source records attributed to D D Stark.

At least 91 records · Page 5Linked to original sources
PubMed1986

Nuclear magnetic resonance of the liver, spleen, and pancreas.

This review includes the initial experience with NMR imaging of the liver, spleen, and pancreas at the University of California, San Francisco, using a prototype 0.35 Tesla system. This experience shows great promise for detection of hepatic metastases using T1-weighted pulse sequences. T2-weighted pulse sequences appear sensitive for detecting cavernous hemangioma of the liver and may allow tissue specific discrimination of the benign lesion from cancer. NMR is also suitable for evaluating diffuse metabolic alterations and is sensitive and specific for the diagnosis of iron overload. Detection of fatty liver requires use of chemical shift techniques as conventional NMR imaging pulse sequences are relatively insensitive. Motion artifacts and lack of an effective bowel contrast agent limits imaging of the pancreas and retroperitoneum, where CT remains the procedure of choice. The normal spleen has longer T1 and T2 relaxation times than liver or pancreas and NMR has not been successful in diagnosing splenic metastases or lymphoma on a routine basis. We conclude that NMR imaging will be valuable in the diagnosis of focal liver disorders; until fast scan techniques and effective magnetic contrast agents are available for oral and/or intravenous use, other abdominal applications will remain limited.

Adenocarcinoma↗
PubMed1986

Magnetic resonance imaging of the kidney.

After a few years of the use of clinically oriented imaging, magnetic resonance (MR) can now be measured against the other cross-sectional radiologic imaging techniques. Its superior sensitivity in demonstrating diseases of the central nervous system and heart has yet to be matched by similar success in the detection of abdominal disease. However, MR is evolving further and improvements in hardware, software, and pulse sequence selection are expected to continue. We present here the experience accumulated to date in the MR evaluation of the kidney in its normal and diseased states.

Adult↗
PubMed1986

Magnetic resonance imaging artifacts: mechanism and clinical significance.

Many types of artifacts may occur in magnetic resonance imaging. These artifacts may be related to extrinsic factors such as patient motion or metallic artifacts; they may be due specifically to the MR system such as power gradient drop off and chemical shift artifacts; they may occur as a consequence of general image processing techniques, as in the case of truncation artifacts and aliasing. Change in patient position, pulse sequence, or other imaging variables may improve some artifacts. Although reduction of some artifacts may require a service engineer, the radiologist has the responsibility to recognize MR imaging problems. The radiologist's knowledge of MR imaging artifacts is important to the continued maintenance of high image quality and is essential if one is to avoid confusing artifactual appearances with pathology.

Diagnostic Errors↗
PubMed1986

Liver metastases: detection by phase-contrast MR imaging.

Forty patients with biopsy-proved metastatic liver cancers were studied by magnetic resonance (MR) imaging using one or more conventional (in-phase) pulse sequences and a corresponding phase-contrast (opposed-phase) pulse sequence. Pulse-sequence performance was quantitated by measuring signal-difference-to-noise (SD/N) ratios between cancerous tissue and liver. The SD/N performance of T2-weighted spin-echo (SE) pulse sequences improved when used with the phase-contrast technique. SE 2,000/30 opposed-phase images showed improved (P less than .001) SD/N in 72% of patients over in-phase images. The SD/N of T1-weighted SE or inversion recovery pulse sequences deteriorated when used with the phase-contrast technique. Changes in measured SD/N correlated well with image appearance and actual lesion detectability in individual cases. Phase-contrast imaging should be employed routinely when T2-weighted SE pulse sequences are relied on to detect liver cancer.

Humans↗
PubMed1986

Detection of hepatic metastases: analysis of pulse sequence performance in MR imaging.

Forty-three patients with liver metastases were imaged using 14 different pulse sequences (average, 7.5 sequences per patient) to allow direct comparison of their performance. "T2-weighted" spin-echo (SE) images, "T1-weighted" inversion recovery (IR) images, and "T1-weighted" SE images were obtained using a wide range of timing parameters. Pulse sequence performance was quantitated by measuring liver signal-to-noise (S/N) ratios and cancer-liver signal difference-to-noise (SD/N) ratios. Data were standardized to reflect a constant imaging time of 9 minutes for all pulse sequences. The SE 2,000/120 (TR [repetition time]/TE [echo time]) sequence resulted in the greatest SD/N ratio of the T2-weighted SE sequences but also yielded the low S/N ratios, poor anatomic resolution, and motion artifacts common to all T2-weighted SE images. IR sequence images were also sensitive to motion artifacts because of the use of a long TR (1,500 msec). Short TR/TE T1-weighted SE sequences (SE 260/18) had the greatest SD/N ratio (P less than .05), S/N ratio, and anatomic resolution. Furthermore, extensive signal averaging appears to be a powerful solution to all types of motion artifacts in the abdomen.

Adenocarcinoma↗
PubMed1986

Duodenal hematoma: the ring sign in MR imaging.

Proper management of duodenal hematoma requires that an accurate diagnosis be made using noninvasive radiological methods. Conventional imaging may be nonspecific if there is no history of trauma or coagulopathy. Two cases of duodenal hematoma that were imaged by magnetic resonance (MR) and computed tomography (CT) are described. In both cases the hematoma had a well-defined concentric ring configuration on MR images, a finding which helped establish the diagnosis. MR imaging may provide tissue-specific characterization of duodenal hematomas.

Aged↗
PubMed1986

Oblique planes of section in MR imaging.

Magnetic resonance (MR) imaging allows freedom in choosing oblique planes of section and rotation of the image plane with respect to the frequency-encoded (F) and phase-encoded (P) dimensions. A general method is described for understanding geometric relationships between the fixed magnetic coordinate system, patient positioning, and the flexible observer's coordinate system. Oblique planes of section are clinically useful in studying organs with an axis of symmetry that is oblique to the magnet coordinate system, such as the heart. Rotation of the image plane can be used to move motion artifacts away from anatomic regions of interest, such as the liver and spine. Appropriate use of oblique section selection and image rotation can improve MR image quality and diagnostic value of the patient study.

Humans↗
PubMed1986

Parathyroid imaging: comparison of double-tracer (T1-201, Tc-99m) scintigraphy and high-resolution US.

Parathyroid scintigraphy using a double-tracer (T1-201, Tc-99m) subtraction technique depicted 17 of 23 (74%) parathyroid adenomas in patients with and without previous neck operations. High-resolution (10-MHz) ultrasound (US) depicted 18 (78%) of these adenomas. Average tumor size depicted by US was 17 X 10 X 8 mm (excluding a giant adenoma) and 19 X 10 X 9 mm by scintigraphy. Alone, neither modality was particularly sensitive in the depiction of primary hyperplasia of the parathyroid glands, but combined techniques were more effective than the use of a single modality. With both US and T1-201 scintigraphy, only two of 23 cases of parathyroid adenoma in the neck were missed, and none of the eight cases of secondary hyperplasia were missed. In 11 patients who had previously undergone neck surgery, parathyroid tumors were identified in eight by either US or double-tracer scintigraphy. Preoperative parathyroid imaging with double-tracer scintigraphy and high-resolution US is suggested for patients with hyperparathyroidism, particularly in those patients who have had previous parathyroid surgery.

Adenoma↗
PubMed1986

MR-guided aspiration biopsy: needle design and clinical trials.

Nonferrous needles of pure brass, titanium, or copper, and ferrous needles of different alloys of stainless steel were analyzed for the size, area, and distribution of the image artifact created when the needles were placed in a 0.6-T magnet. Results demonstrated that a stainless steel prototype needle (type 316) would be visible on magnetic resonance images and would provide an artifact similar to that seen in computed tomographic-guided biopsies. Further testing of this prototype included assessment of the effect on the artifact when changes were made in annealing properties, gauge, length, needle-tip geometry, pulse sequence, and orientation relative to the magnetic field. To date, three human liver biopsies have been successfully and safely performed using a stainless steel type 316 needle.

Aged↗
PubMed1986

MRI of the Budd-Chiari syndrome.

Five of six patients with angiographically proved Budd-Chiari syndrome (hepatic venous outflow obstruction) showed multiple specific MRI abnormalities: striking reduction in caliber or complete absence of the hepatic veins, "comma-shaped" intrahepatic collateral vessels, and/or marked constriction of the intrahepatic inferior vena cava. The sixth patient had angiographically proven sinusoidal hepatic venous obstruction and patent central hepatic veins; MRI showed ascites but revealed no specific features of the Budd-Chiari syndrome. Patients with end-stage cirrhosis also showed compressed, distorted hepatic veins; however, these cirrhotic livers were distinguished by their small size, nodular surface, and extrahepatic collateral varices. In patients without cirrhosis or the Budd-Chiari syndrome, normal hepatic, portal, and inferior caval veins were routinely seen when technically adequate MRI examinations were obtained (94 of 100 cases). Four of the six patients with Budd-Chiari syndrome had been treated surgically. In three, MRI identified patent portocaval shunts. In the fourth, angiographically confirmed shunt stenosis was demonstrated by MRI.

Adult↗
PubMed1986

Staging rectal cancer by MR and CT.

Sixteen patients with known rectal cancer were evaluated and staged with CT and MR, and at surgery. Detailed evaluation of the pathologic specimens was performed and correlated with CT and MR to determine the accuracy of staging. Most of the cases were advanced stages, and both CT and MR were equally effective in staging. Prone positioning using an air-distension technique was equally important for CT and MR examinations. Because of a positive contrast material (iodine), adequate CT examinations could be performed without prior bowel preparation; however, bowel cleansing was necessary for MR examinations. Both techniques could identify the primary tumor and invasion into perirectal fat and local organs. Neither CT nor MR were able to assess the extent of bowel-wall infiltration or tumor spread to normal size perirectal lymph nodes.

Air↗
PubMed1986

Dynamic spin-echo MRI of liver cancer using Gadolinium-DTPA: animal investigation.

An animal model of liver cancer was used to demonstrate that with a fast MRI technique, Gadolinium-DTPA increases tumor-liver contrast. A spin-echo pulse sequence with short repetition (TR) and echo-delay (TE) times (TR 250/TE 15/Excitations 1) has a scan time of 0.6 min, which allows early dynamic postcontrast infusion imaging. This is necessary to capture peak compartmental differences when an extracellular contrast agent such as Gadolinium-DTPA is used. This short TR/short TE pulse sequence also increases T1-dependent tissue contrast over the traditional (inversion recovery or spin echo) T1-weighted pulse sequences. Our studies suggest a significant potential for improved detection of liver metastases with Gadolinium-DTPA-enhanced liver MRI.

Adenocarcinoma↗
PubMed1986

Boundary artifact due to truncation errors in MR imaging.

A boundary artifact in MR images due to truncation of the infinite Fourier series necessary to encode tissue discontinuities was investigated by using doped water phantoms and normal volunteers. All images were obtained on 0.3-T permanent and 0.6-T superconducting MR imagers with varying phase and frequency sampling rates. The artifact appeared in both the phase and frequency encoding direction as parallel lines or ringing adjacent to borders or tissue discontinuities. This was unlike motion artifacts, which occur predominantly in the phase direction, and chemical shift misregistration errors, which are most pronounced in the frequency direction. Increasing the sampling frequency from 128 to 512 resulted in higher frequency ringing and more rapid drop-off in amplitude. Low-pass digital filtering also decreased the ringing at the expense of fine detail. The truncation of the infinite Fourier series necessary to encode edges to the 128-512 terms used for most MR imaging produces the artifact. It is important to recognize this common artifact and not mistake it for patient motion or disease.

Diagnostic Errors↗
PubMed1985

Magnetic resonance imaging: present and future applications.

Magnetic resonance (MR) imaging has created considerable excitement in the medical community, largely because of its great potential to diagnose and characterize many different disease processes. However, it is becoming increasingly evident that, because MR imaging is similar to computed tomography (CT) scanning in identifying structural disorders and because it is more costly and difficult to use, this highly useful technique must be judged against CT before it can become an accepted investigative tool. At present MR imaging has demonstrated diagnostic superiority over CT in a limited number of important, mostly neurologic, disorders and is complementary to CT in the diagnosis of certain other disorders. For most of the remaining organ systems its usefulness is not clear, but the lack of ionizing radiation and MR's ability to produce images in any tomographic plane may eventually prove to be advantageous. The potential of MR imaging to display in-vivo spectra, multinuclear images and blood-flow data makes it an exciting investigative technique. At present, however, MR imaging units should be installed only in medical centres equipped with the clinical and basic research facilities that are essential to evaluate the ultimate role of this technique in the care of patients.

Abdomen↗
PubMed1985

Magnetic resonance imaging of constrictive pericardial disease.

Gated magnetic resonance imaging of 5 patients with suspected constrictive pericardial disease was performed using a superconducting magnet operating at 0.35 Tesla. Results were compared with those of echocardiography and hemodynamic measurements in all patients, with chest films in 5, computerized tomography in 2 and with histologic findings in 3. Pericardial thickness exceeded 5 mm in 4 patients and was 5 mm in 1 patient. Absence of magnetic resonance signal from the thickened pericardium was observed with extensive calcific deposits, and increased intensity of the thickened pericardium was associated with inflammatory disease. Dilatation of the right atrium, venae cavae and hepatic veins, and right ventricular narrowing was observed in all patients. The ventricular septum was straight in all patients. Magnetic resonance imaging allows both measurement of pericardial thickness and depicts internal cardiac anatomy without exposure to radiation or use of contrast medium. Satisfactory imaging with a large field of view can be performed in the presence of lung disease, thoracic deformity or surgical "hardware"--conditions that limit echocardiography and computerized tomography. The inherently 3-dimensional data permit imaging in any plane without loss of resolution. Thus, magnetic resonance appears to be the noninvasive method of choice for the diagnosis of constrictive pericardial disease.

Calcinosis↗
PubMed1985

Magnetic resonance imaging and spectroscopy of hepatic iron overload.

Experimental animals that had been given excess iron in their diet were studied by magnetic resonance (MR) imaging in vivo and by magnetic resonance (MR) spectroscopy in vitro. Hepatic iron overload in patients with transfusional iron excess was studied by MR imaging, and isolated iron protein fractions were studied in vitro by MR spectroscopy. The spin echo image intensity of livers with iron overload was decreased because of the extreme decreases in T2 compared with normal; T1 was decreased only moderately. The relaxation rates 1/T2 and 1/T1 both showed a linear relationship to hepatic iron levels. Ferritin solutions showed moderate decreases in T2 and mild decreases in T1. The T2 relaxivity of ferritin, which is due to the iron core rather than the apoferritin protein shell, does not appear sufficient to account for the extreme decrease in T2 observed in hepatic iron overload. Low molecular weight cytosol iron is present in lower concentrations than ferritin but potentially has much greater relaxivity and may contribute to the MR findings. These techniques may be useful in other studies of iron metabolism.

Adolescent↗
PubMed1985

Obstetrical magnetic resonance imaging: maternal anatomy.

Eleven patients whose pregnancies were at 34-36 weeks of gestational development underwent magnetic resonance (MR) imaging. Images of the maternal pelvis were assessed for anatomical changes of pregnancy in comparison with MR images of five non-pregnant volunteers. The relationship of the fetal presenting part to the internal os of the cervix was seen in all patients. Effacement of the cervix was identified when present. The maternal spine demonstrated disk abnormalities in nine patients. Changes in venous flow patterns were readily identified in all patients. The inferior vena cava was flattened or obliterated, a high signal was present in the iliac vessels (TE 56), and large collateral vessels were present.

Adult↗