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Biomedical subjects

A J Dwyer

Publications and source records attributed to A J Dwyer.

At least 19 recordsLinked to original sources
PubMed1992

Hydrated clearance of gadolinium-DTPA as a measurement of glomerular filtration rate.

Technetium (99mTc)-diethylene triamine pentaacetic acid (DTPA) hydrated clearance studies are accurate for determining GFR but require special facilities for handling and measuring samples. We investigated the potential of a non-radioactive paramagnetic analog, Gadolinium (Gd)-diethylene triamine pentaacetic acid (DTPA), an approved NMR contrast agent, as a glomerular filtration marker. Instead of relying on the radioactivity of technetium, this test is based on the fact that gadolinium induces alterations in the NMR T1 relaxation times in blood and urine samples. Ninety patients underwent simultaneous determinations of GFR using 1 mCi of Tc-DTPA and 0.05 mmol/kg Gd-DTPA (Berlex Labs) IV. The patients were hydrated with oral and intravenous fluid. Following a one hour equilibrium period, three or four consecutive urine collections were obtained; plasma samples were acquired at the beginning and end of each approximately 20-minute interval. 99mTc-DTPA radioactivity was determined with a scintillation counter. T1 relaxation times were measured on a 10 MHz NMR spectrometer. These were converted to Gd-DTPA concentration by comparison with standard solutions. The Gd-DTPA derived GFR closely approximated the 99mTc-DTPA derived GFR which ranged from 15 to 147 ml/min. The equation and correlation coefficient of the regression line is y = 1.04 x -2.2, r = 0.94. Thus, Gd-DTPA is a safe, non-radioactive indicator of GFR that may provide an alternative renal clearance method for clinical studies of progressive renal disease and nephrotoxicity.

Contrast Media↗
PubMed1992

Pulmonary metastases: MR imaging with surgical correlation--a prospective study.

The sensitivity of magnetic resonance (MR) imaging for detection of pulmonary metastases in 11 patients scheduled for thoracotomy and curative resection of metastases was evaluated with a prospective, controlled study. MR imaging performed at 0.5 T was compared with chest radiography, computed tomography (CT), and thoracotomy in 12 cases. (One patient had two separate occurrences of pulmonary metastases.) All images were interpreted in blinded fashion. When all MR sequences were interpreted together, MR imaging enabled correct identification of all patients with pulmonary nodules (100%). CT enabled detection of at least one nodule in all 12 cases (100%) by design; the sensitivity of chest radiography was only 64%. For individual nodules, MR imaging was at least as sensitive as CT (P2 less than .25 [two-sided value]) and significantly more sensitive than chest radiography (P2 less than .01). Among all MR sequences, short inversion time inversion-recovery sequences had the highest sensitivity for detection of individual nodules (82%).

Adult↗
PubMed1992

Distinction between hyperaldosteronism due to bilateral hyperplasia and unilateral aldosteronoma: reliability of CT.

Hyperaldosteronism due to a unilateral adenoma must be distinguished from hyperaldosteronism due to bilateral hyperplasia to enable the proper choice between surgical treatment (for adenoma) or medical treatment (for hyperplasia). To compare the efficacy of computed tomography (CT) and adrenal venous sampling, both examinations were performed in 24 patients with primary aldosteronism. All patients with a diagnosis of adenoma based on findings at venous sampling underwent adrenalectomy. The CT-based diagnosis was unilateral aldosteronoma in 17 patients and hyperplasia in seven patients. On the basis of venous sampling, unilateral adenoma was diagnosed in 22 patients; this diagnosis was confirmed by means of unilateral adrenalectomy in 21 patients. The most common error was diagnosis of hyperplasia based on the presence of bilateral nodules on CT scans: In six of seven patients with such a diagnosis, venous sampling and subsequent surgery revealed a unilateral adenoma. In hyperaldosteronism with multiple bilateral nodules, CT cannot reliably permit distinction between hyperplasia and adenoma.

Adenoma↗
PubMed1992

Mapping of brain tumor metabolites with proton MR spectroscopic imaging: clinical relevance.

Brain tumor metabolism was studied with hydrogen-1 magnetic resonance spectroscopy and positron emission tomography with fluorine-18 fluorodeoxyglucose in 50 patients. N-acetylaspartate (NAA) was generally decreased in tumors and radiation necrosis but was somewhat preserved at neoplasm margins. Choline was increased in most solid tumors. Solid high-grade gliomas had higher normalized choline values than did solid low-grade gliomas (P < .02), but the normalized choline value was not a discriminator of tumor grade, since necrotic high-grade lesions had reduced choline values. Serial studies in one case showed an increase in choline as the glioma underwent malignant degeneration. Choline values were lower in chronic radiation necrosis than in solid anaplastic tumors (P < .001). In two cases studied before and after treatment, clinical improvement and a reduction in choline followed therapy. Lactate is more likely to be found in high-grade gliomas, but its presence is not a reliable indicator of malignancy.

Adolescent↗
PubMed1991

Matchmaking and McNemar in the comparison of diagnostic modalities.

Comparative studies of radiologic techniques commonly yield matched data due to the ease and desirability of performing all of the techniques on each of the patients. The two-by-two matched data array and the McNemar analysis provide a succinct format for the presentation and proper analysis of matched comparisons of binary (positive and negative) test results. When comparing tests, it is essential not to rely on just the statistical significance of the differences in sensitivities (or specificities); the magnitude of the differences must also be assessed. Confidence intervals provide a useful form of estimation by providing a range of plausible values and an indication of the precision of the estimate. The matched data array also indicates the complementarity of the diagnostic tests being compared.

Diagnostic Imaging↗
PubMed1991

Detection of ACTH-producing bronchial carcinoid tumors: MR imaging vs CT.

Adrenocorticotrophic hormone (ACTH)-producing bronchial carcinoid tumors tend to occur in the middle third of the lung adjacent to pulmonary vessels. Because they cause signs and symptoms when quite small (by virtue of their ACTH production), they may not be detected by CT. MR imaging was performed in 10 consecutive patients with surgically proved ACTH-producing bronchial carcinoid tumors in order to test the ability of MR to clarify equivocal or indeterminate findings on CT examinations. All bronchial carcinoid tumors had high signal intensity on T2-weighted and short-inversion-time inversion-recovery images, facilitating their distinction from pulmonary vasculature. In eight patients, the CT and MR images were equivalent in the detection of bronchial carcinoid tumors. In two patients, MR showed tumors in the middle third of the lung that were equivocal on CT. MR imaging may distinguish small bronchial carcinoid tumors from adjacent pulmonary vessels in the central third of the lung at a time when the CT study is nondiagnostic or equivocal.

Adrenocorticotropic Hormone↗
PubMed1990

von Hippel-Lindau disease: radiologic screening for visceral manifestations.

The visceral manifestations of von Hippel-Lindau (VHL) disease can cause significant morbidity and mortality. The authors prospectively screened 37 persons from a single kindred. Twenty-five subjects underwent abdominal ultrasound (US), contrast material-enhanced abdominal computed tomography (CT), and nonenhanced abdominal magnetic resonance (MR) imaging. Eight subjects younger than 16 years of age underwent abdominal US and MR imaging only. Scrotal US was employed in 25 male patients. Eleven subjects had renal cysts or tumors. Contrast-enhanced CT depicted renal abnormalities in 10 of these subjects, US in seven, and MR imaging in nine. Among 12 subjects with pancreatic cysts or tumors, CT showed pancreatic abnormalities in all 12, US in nine, and MR imaging in nine. Three subjects (mean age, 34.5 years) had renal tumors, and three had pancreatic masses. Scrotal US revealed epididymal cystadenomas in seven subjects; two of these tumors were surgically verified. A combination of contrast-enhanced CT and scrotal US in male patients appears to be the best way to screen for visceral manifestations of VHL disease.

Adolescent↗
PubMed1990

Detection of malignant bone tumors: MR imaging vs scintigraphy.

One hundred six patients with a known or suspected diagnosis of bone cancer (11 patients with biopsy-proved primary tumors, 95 patients with metastatic disease) were evaluated with scintigraphy and MR imaging to determine the relative sensitivity of each technique in the detection of bone disease. MR imaging was performed at 0.5 T as part of the entry evaluation into Intramural Research Board protocols (30%), for evaluation of cord compression, or because of an equivocal scintigram. MR was performed with T1-weighted (e.g., 300-500/10-20 [TR/TE]), T2-weighted (e.g., 2000/80) spin-echo (SE), and a short-TI inversion recovery (STIR) pulse sequence. Scintigrams were performed with 99mTc-methylene diphosphonate. A retrospective analysis showed that in 30 (28%) of 106 patients, MR imaging performed over a limited region of interest revealed a focal abnormality consistent with tumor that was not observed on scintigraphy. Only one patient had an abnormality on scintigraphy, caused by a metastasis, that was not found on MR images. In 73 (69%) of the 106 patients, the results of MR imaging and scintigraphy were equivalent; in 41 cases results of both techniques were normal. A McNemar analysis of the discordant cases showed MR imaging to be more sensitive than scintigraphy was (p less than .001). Our results suggest that although MR imaging has a greater sensitivity in detecting focal disease, scintigraphy is still the most useful screening test for evaluating the entire skeleton. MR imaging should be reserved for clarification of scintigraphic findings when suspicion is high for tumor.

Adolescent↗
PubMed1989

Renal calculi after shock wave lithotripsy: US evaluation with an in vitro phantom.

Fragments of renal calculi from patients who had undergone extracorporeal shock wave lithotripsy (ESWL) were embedded in an in vitro tissue-equivalent ultrasound (US) phantom to assess (a) the accuracy with which such fragments could be measured; (b) the influence of stone composition, stone depth, and transducer frequency; and (c) the effect of fragment "clumping" on size determinations and acoustic shadowing. Fragments as small as 0.8 mm in diameter could be detected at 7.5 MHz, although a practical limitation of 1-2 mm for lower transducer frequencies (3.5 and 5.0 MHz) was observed. Fragment diameter tended to be overestimated with US by a mean of 1 mm. Transducers of 5 and 7.5 MHz were more accurate in determination of size than 3.5-MHz transducers. Struvite fragments were less echogenic and were therefore measured more accurately, but smaller struvite fragments were less detectable than other fragment types. Fragment "clumping" led to significant overestimation of residual stone size even when small fragments were separated by as much as the distance equal to the diameter of one fragment. This study demonstrates that even under the best circumstances the disadvantages of US in assessing residual stone disease are significant.

Humans↗
PubMed1989

Liver metastases: detection with MR imaging at 0.5 and 1.5 T.

Nineteen patients with known liver metastases were examined with two magnetic resonance (MR) pulse sequences at 0.5 T and three pulse sequences at 1.5 T. In addition, the patients were studied with computed tomography (CT) enhanced with ethiodized oil emulsion-13 (EOE-13). At 0.5 T a spin-echo (SE) 300/22 (repetition time/echo time, msec) sequence prospectively demonstrated 92.4% of the detectable liver metastases, while an SE 2,000/80 sequence showed 52.1% of the lesions. At 1.5 T, an SE 300/25 sequence depicted 68.3% and an SE 2,000/80 sequence 71.6%, while the more T1-weighted inversion recovery (IR) 2,000/600 (repetition time/inversion time, msec) sequence demonstrated 89.5% of the lesions. EOE-13 CT scans depicted 93.3%. These findings suggest that T1-weighted imaging is as successful at demonstrating liver metastases at 1.5 T with an IR 2,000/600 sequence as at 0.5 T with an SE 300/22 sequence. At both field strengths, MR imaging of the liver is comparable to state-of-the-art CT.

Humans↗
PubMed1989

Dynamic Gd-DTPA-enhanced MR imaging of the kidney: experimental results.

To determine the normal appearance of dynamic enhanced renal magnetic resonance (MR) images, 25 rabbits were injected with Gd-DTPA and 32 consecutive gradient-recalled images were acquired. Several rabbits were also imaged in dehydrated (five animals) and overhydrated (seven animals) states. A reproducible renal enhancement pattern is observed that can be divided into three phases. During the first phase, a peripheral dark band appears, probably representing arrival of Gd-DTPA within the arterioles and vasa recta. The second phase begins as a second dark band migrating centripetally toward the medulla; this likely represents the concentration of Gd-DTPA in the descending limb of the loop of Henle. The third phase is characterized by a gradual darkening in the papilla, probably caused by concentration of Gd-DTPA within the collecting ducts. Hydration status influences the duration of these phases. These observations can be explained by the anatomy and physiologic characteristics of the nephron, as well as the MR characteristics of Gd-DTPA at different concentrations.

Animals↗
PubMed1989

Gastrinomas: comparison of MR imaging with CT, angiography, and US.

In this prospective study, magnetic resonance (MR) imaging was used to localize gastrinoma in 24 patients with Zollinger-Ellison syndrome. The results were confirmed by means of either surgery or percutaneous liver biopsy and compared with results of computed tomographic (CT) scanning, selective abdominal angiography, and abdominal ultrasound (US). For primary extrahepatic gastrinoma (intra-or extrapancreatic), MR imaging had a sensitivity of 20% and a specificity of 100%, with a positive predictive value of 100% and a negative predictive value of 11%. For metastatic gastrinoma in the liver, MR imaging had a sensitivity of 43% and a specificity of 100%, with a positive predictive value of 100% and a negative predictive value of 81%. The ability of MR imaging to depict extrahepatic gastrinomas was directly related to tumor size; no tumors smaller than 1 cm were detected, and 50% of tumors 3 cm or larger were detected. MR imaging was as effective as abdominal US but less effective than either CT scanning or selective abdominal angiography for the detection of extrahepatic gastrinoma. In seven patients with hepatic gastrinoma, three gastrinomas were detected with MR imaging and with abdominal US, while five were detected with CT scanning and with selective abdominal angiography. These results indicate that, at the present time, MR imaging is generally not useful in the initial attempt to localize gastrinomas.

Adult↗
PubMed1989

Prospective evaluation of hepatic imaging studies in the detection of colorectal metastases: correlation with surgical findings.

Nineteen patients with isolated colorectal liver metastases were preoperatively evaluated with five hepatic imaging studies. The results of these studies were correlated with operative findings. One study involved the use of EOE-13, an intravenously administered lipid contrast agent that enhances liver parenchyma on computed tomography (CT) scans (EOE-CT). Another study, arterial portography (AP-CT), was performed with injection of a water-soluble contrast agent into the superior mesenteric artery during CT scanning. Delayed CT scanning (DS-CT) was completed 4 hours after AP-CT. In addition, T1- and T2-weighted magnetic resonance imaging (MRI) (T1-MRI, T2-MRI) scans were done. All patients subsequently underwent laparotomy with identification of 78 lesions. A lesion-by-lesion analysis revealed that the sensitivity of EOE-CT (83%), AP-CT (78%), DS-CT (82%), and T1-MRI (84%) was comparable. T2-MRI had a significantly lower sensitivity (64%) compared with EOE-CT, DS-CT, and T1-MRI. The false-positive rate for AP-CT was 31%, which was significantly higher than that of all other studies. The T1-MRI examination had the lowest false-positive rate and proved to be the best hepatic imaging study in the detection of colorectal metastases. EOE-CT and DS-CT were comparable, whereas AP-CT and T2-MRI proved to be inferior tests.

Colorectal Neoplasms↗
PubMed1988

Macronodular adrenal hyperplasia in Cushing disease.

Computed tomographic (CT) scans of the adrenal glands were obtained in nine patients with Cushing disease as a result of an adrenocorticotropic hormone (ACTH)-secreting pituitary adenoma and macronodular hyperplasia of the adrenal glands. The findings were compared retrospectively with those in six patients with Cushing syndrome as a result of an autonomous adrenal adenoma and 16 with Cushing syndrome as a result of ectopic ACTH production. Seven of nine patients with macronodular adrenal hyperplasia had hyperplastic adrenal glands in addition to single or multiple focal adrenal nodules. The six patients with hypercortisolism caused by an autonomous adrenal adenoma showed atrophic (four patients) or normal (two patients) ipsilateral and contralateral adrenal glands. Fourteen of 16 patients with the ectopic ACTH syndrome had hyperplasia of the adrenal glands without nodularity, and only two had focal nodules.

ACTH Syndrome, Ectopic↗
PubMed1988

Spinal cord artifacts from truncation errors during MR imaging.

The significance of linear regions of altered signal intensity that appear in sagittal magnetic resonance (MR) images along the length of the spinal cord was investigated. Examinations were performed on ten healthy volunteers and one patient with spinal cord edema. A 0.5-T or a 1.5-T MR system was used. Sampling-related effects (Gibbs phenomenon) at spinal cord edges and cerebrospinal fluid interfaces can lead to different signal patterns within the spinal cord and canal. These artifacts cause problems in interpretation, especially with the use of small object-to-pixel size ratios, by obscuring anatomy and simulating pathologic conditions such as pseudosyringes. Analysis of these intensity variations and of their dependence on sampling may improve the clinical accuracy of MR imaging.

Humans↗