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Biomedical subjects

D Thickman

Publications and source records attributed to D Thickman.

At least 37 records · Page 2Linked to original sources
PubMed1989

White matter lesions: role of spin density in MR imaging.

To study the effect of hydrogen spin density (N[H]) on magnetic resonance (MR) image contrast in white matter disease of the brain, T1, T2, and N[H] values were determined for normal white matter and idiopathic white matter lesions (IWMLs) in 21 patients by using multiple spin-echo (SE) sequences. T1 values of IWMLs were significantly greater than those of normal white matter in all patients studied, and T2 values of IWMLs were significantly greater in 20 of 21 patients. N[H] values of IWMLs were greater in 20 of 21 patients, with statistically significant differences from those of normal white matter in 17 of those 20 patients. Averaged over all 21 patients studied, N[H] values of IWMLs were 20% higher than N[H] values of normal white matter. The effect of unequal N[H] values on contrast between IWMLs and normal tissues is to reduce contrast on short SE sequences with a short repetition time (TR) and a short echo time (TE), while enhancing contrast between IWMLs and normal tissues on long TR/TE SE sequences. Elevated N[H] values in IWMLs have a minimal effect on contrast in conventional inversion-recovery (IR) sequences but substantially enhance contrast between IWMLs and normal brain tissues in short inversion time IR sequences.

Brain↗
PubMed1988

Effect of phase-encoding direction upon magnetic resonance image quality of the heart.

In order to optimize overall cardiac image quality on MR images experienced observers were asked to rank and rate MR images of the heart. The effect of phase-encoding direction and use of cardiac triggering with and without respiratory gating was examined in three orthogonal imaging planes. Results indicate that use of both respiratory and cardiac gating yields the best images. Adequate images of the heart can be obtained without respiratory gating. The quality of images of the heart can be optimized by proper selection of the direction of the phase-encoding gradient. These are improved by using horizontal phase encoding in the sagittal plane and vertical phase encoding in transverse and coronal planes.

Heart↗
PubMed1988

Vicarious excretion of water-soluble contrast media into the gallbladder in patients with normal serum creatinine.

Ten patients with normal serum creatinine and no evidence of acute cholecystitis were found to have vicarious excretion of water-soluble contrast media into the gallbladder 20 minutes to 72 hours after injection. Eight of the ten had unilateral renal pathology. Two patients, however, had bilaterally normal kidneys. The patients had been injected with either diatrizoate, iothalamate, or iodamide. The mechanisms and pathophysiology of vicarious contrast excretion are discussed. The vicarious excretion of intravascular contrast in the gallbladder does not in itself indicate renal or hepatobiliary disease. Although commonly associated with unilateral renal pathology, vicarious gallbladder excretion of urographic contrast may be a normal variant in some patients.

Adolescent↗
PubMed1987

Searching for lung nodules. A comparison of human performance with random and systematic scanning models.

The contrast sensitivity of the retina is greatest in the center and decreases rapidly toward the periphery. Therefore, the detection of low-contrast lung nodules depends upon the manner in which the image is sampled by retinal receptors as eye fixations jump across the image during scanning. The scanning performance of two radiologists was compared with two computed models, a systematic and a random scanner. Although radiologists do not seem to have random scanning patterns, their coverage of the image was matched more closely by the random model. This suggests that radiologists employ a scanning strategy that is designed to cover the image of the lungs in a minimum time using the smallest possible visual field. The visual field size that is most effective in detecting nodules during search has a radius of 3.5 degrees visual angle. Nodule detection may be limited by basic neurologic constraints on human scanning performance.

Computer Simulation↗
PubMed1987

Magnetic resonance imaging to evaluate patency of aortocoronary bypass grafts.

To assess the efficacy of magnetic resonance (MR) imaging in evaluating graft patency after coronary bypass surgery, 20 patients who had prior surgery (average 5.5 years, range 1.5 to 14) and recent cardiac catheterization because of chest pain were studied. No patient had surgical intervention or change in symptoms in the time interval between catheterization and MR imaging. These 20 patients had a total of 47 grafts, defined as proximal anastomoses: 20 to the left anterior descending or diagonal artery (LAD), 13 to the left circumflex artery marginal branches (LCX), and 14 to the right coronary artery or posterior descending artery (RCA). The patients underwent cardiac and respiratory gated MR scans in a 0.5 tesla magnet with an echo time of 22 msec and two repetitions in a 128 X 256 matrix. In-plane resolution was 2.7 mm. Every patient had a scan in the transaxial plane and some underwent scanning in the sagittal and coronal planes as well. A graft was considered patent by MR when a signal-free lumen was visualized in an anatomic position consistent with that of a bypass graft, had a lumen larger than the native vessels, was seen on more than one slice, and was seen at a level higher than that of the native vessels. If a known graft was not seen it was considered occluded. The scans were interpreted by consensus of two physicians aware of the operative but not the cardiac catheterization data.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1987

Prior carotid surgery does not affect the reliability of landmarks for location of the internal jugular vein.

Twenty-one volunteer subjects who had undergone prior carotid endarterectomy (CEA) agreed to an ultrasound study of the neck. The transducer was held as one would hold a cannulating needle and ultrasound images were obtained of the great vessels in the neck. Each of two cannulating techniques was simulated on each side of every patient's neck. Photographs of the ultrasound images were analyzed to score "hit" or "miss" for the internal jugular vein (IJV) and the carotid artery (CA), and to measure both the angle between these vessels and the distance from the skin to the IJV. In 11 subjects, the effect of a Valsalva maneuver on IJV width was also determined. Owing to bilateral CEA in 9 of the 21 subjects, there were 12 studies of nonsurgical sides (NSS) and 30 studies of surgical sides (SS). SS and NSS hit frequencies were statistically indistinguishable both for the IJV and the CA. In no photograph did the IJV lie medial to the CA. A Valsalva maneuver did not change IJV width on either the SS or the NSS. These data show that prior CEA does not affect the location of the IJV. Tissue alterations or adhesions may render actual IJV cannulation more difficult or risky. The data suggest but do not prove that prior CEA may not increase the incidence of CA puncture under clinical conditions.

Carotid Arteries↗
PubMed1986

Magnetic resonance imaging of avascular necrosis of the femoral head.

This study investigates the role of magnetic resonance imaging (MR) in identifying avascular necrosis (AVN) of the femoral head and in monitoring its therapy. The detection of AVN, particularly in its early stages, is imperative to give therapeutic intervention the best opportunity for successful management. The results of magnetic resonance imaging are compared with those of the standard diagnostic modalities in evaluation of patients with the lesion. Examinations were performed at 0.12T with a repetition time (TR) of 143 ms and times to echo (TE's) of 10 or 20 ms. This study represents a retrospective review of 90 hips which were examined in 45 consecutive patients. Of these, 52 hips were biopsied as part of treatment. MR was shown to be sensitive in the detection of AVN. Comparison of MR with radionuclide imaging showed comparable sensitivity and specificity. MR was also noted to be sensitive in the detection of early AVN. Preliminary results suggest that MR can monitor treatment of the affected hip, and may even be able to predict patient response to therapy. Although further work is necessary to determine the role of MR in the evaluation of the patient presenting with hip pain, MR is a sensitive method in detecting AVN and in monitoring its course in patients suspected of having the disease.

Adult↗
PubMed1986

Sonographic assessment of the endometrium in patients undergoing in vitro fertilization.

Sonography has an important role in the care of infertile patients undergoing in vitro fertilization. Unlike the ovarian follicle, sonographic changes in the endometrium during induction have not been extensively investigated. To determine whether changes in endometrial thickness or changes in endometrial texture would predict subsequent pregnancy, a randomized, double-blind review of 320 studies was performed. None of the endometrial patterns nor any particular change from one pattern to another during induction was predictive of subsequent pregnancy. Although differences in endometrial thickness between non-pregnant and subsequently pregnant patients were noted, on an individual basis, endometrial thickness was not a useful predictor.

Double-Blind Method↗
PubMed1986

Postoperative peritoneal cysts.

Peritoneal cysts are an infrequent postoperative complication. Few cases have been reported in the literature. This paper presents four cases seen after gynecologic operations. The cysts occurred 1.5 to 8 months postoperatively. The patients presented with pain and a large pelvic mass. No patient showed clinical or laboratory evidence of acute inflammation. Ovarian neoplasm was the leading diagnosis in three cases; the correct preoperative diagnosis of peritoneal cyst was made in only one case. Three patients were managed successfully with resection. One patient was treated with percutaneous drainage, though nine months was required for complete resolution. There were no recurrences at one-year follow-up.

Adult↗
PubMed1985

Vascular occlusions detected by magnetic resonance imaging.

Early experience with magnetic resonance imaging (MRI) indicates that it is well suited as a noninvasive vascular imaging modality. Blood flow at physiologic velocities results in a low signal within the vessel lumen and this property allows the separation of flowing blood from surrounding soft tissues. While flow effects, aneurysms, and mural lesions have been emphasized in the literature, vascular occlusions have received less attention. We evaluated 21 patients with documented venous or arterial occlusions on a 0.12-T developmental resistive unit. Venous occlusions caused by thrombus generally appeared as focal regions of increased signal. In 3 of 10 cases the venous thrombus itself could not be identified but the absence of a low-signal lumen in a normal location confirmed the impression of thrombus. In 2 of 17 venous occlusions a rim of low signal was noted around the thrombus. Venous collaterals were commonly seen. Tumor thrombus tended to have signal characteristics similar to the main bulk of the tumor from which it arose. There were four arterial occlusions including two cases of emboli, one arteriosclerotic occlusion, and one case of tumor invasion. Vascular calcifications, clearly evident on plain radiographs, were not seen on MRI. MRI appears to be a potentially useful noninvasive means of detecting vascular occlusions.

Adolescent↗
PubMed1985

Controversies in the radiologic diagnosis of pelvic malignancies.

Although vast differences exist among the many pelvic malignancies, several unifying concepts emerge from this discussion. First, there is a different role for diagnostic imaging for each type of pelvic malignancy. The radiologist should be aware that although the radiographic findings may be similar, the clinical impact varies greatly with a particular tumor. Second, although clinical staging is notoriously inaccurate, nevertheless diagnostic imaging techniques only improve upon but do not replace it because of false-positive and false-negative results. Third, because of the high false-negative rates of most of the modalities in use, negative studies do not in fact rule out the presence of disease. A surgical procedure may still be needed. Finally, several new techniques, including MRI and transrectal or transurethral ultrasound, may improve the accuracy rates. These developments will probably further enliven the controversies surrounding the radiologic evaluation of pelvic malignancies.

Female↗
PubMed1984

Nuclear magnetic resonance imaging in gynecology.

Nuclear magnetic resonance proton imaging is a new imaging technique that holds promise for gynecologic diagnosis. Without the use of ionizing radiation, it provides images with excellent definition of the major pelvic organs. The extent and nature of disease are well demonstrated. In this report, an introduction to the principles of nuclear magnetic resonance imaging is given and several clinical examples that reveal the potential uses of nuclear magnetic resonance imaging in the female pelvis are shown.

Adult↗
PubMed1984

MR imaging of the mediastinum: a retrospective comparison with computed tomography.

Magnetic resonance (MR) imaging of the mediastinum was performed with a 0.12 T resistive magnet and compared with the results of CT. On T1 weighted images with partial saturation technique, soft tissue masses, lymphadenopathy, lipomatosis, and vascular anatomy were comparable with MR and CT imaging in 19 of 30 patients (63.3%). In the remaining 11 patients only slight differences between the two modalities were observed. Our experience suggests that MR imaging at low field strength is equivalent to CT in the morphologic assessment of the mediastinum without the need for administration of intravenous contrast medium or exposure to ionizing radiation.

Humans↗
PubMed1984

CT imaging of the unusually shaped bladder.

In the CT evaluation of a cystic pelvic mass it is important to identify the urinary bladder and assess its relationship to the mass. Although this is generally an easy task, we have encountered cases where delayed opacification of the bladder created diagnostic difficulties. Following intravenous contrast medium infusion, patients with normal renal function may have unopacified bladders due to (a) delayed transit from kidney to bladder and (b) rapid CT imaging of the bladder before opacification can occur. If one is aware of these problems, diagnostic dilemmas may be reduced by obtaining delayed scans of the pelvis or by obtaining postvoid films. Two cases are presented to illustrate these points.

Aged↗
PubMed1984

MR imaging of cerebral abnormalities in utero.

In view of the lack of ionizing radiation, ability to image in a variety of planes, and high contrast resolution, magnetic resonance (MR) imaging may have a role in obstetrical management. Three fetuses with severe cerebral abnormalities were studied by MR in utero. The findings were correlated with ultrasound examinations and with autopsy results. Ventricular dilatation and progression of hydrocephalus were detected by MR. Although fetal motion may affect image quality, diagnostically useful images were obtained with imaging times of 2.5 min.

Autopsy↗
PubMed1984

Magnetic resonance evaluation of hydronephrosis in the dog.

The ability of magnetic resonance (MR) imaging to detect and distinguish various stages of obstruction in the canine kidney was investigated. MR images were obtained at acute, subacute, and chronic stages of experimentally produced hydronephrosis. The renal cortex was distinguished from the renal medulla in the normal dog and in the acute and subacute stages of hydronephrosis. T1 relaxation times of the renal cortex and medulla were measured in vitro in 14 normal and nine experimental animals. These values were used to compute the amount of tissue contrast between the cortex and medulla and were compared with the degree of corticomedullary differentiation seen in the image. A relationship was noted between increasing T1 values and increasing water content. Corticomedullary contrast decreased with obstruction. The variation in corticomedullary image contrast may be useful for assessing the duration of hydronephrosis.

Animals↗
PubMed1984

Nongated cardiac magnetic resonance imaging: preliminary experience at 0.12 T.

Nongated cardiac magnetic resonance imaging (MRI) has been reported previously to be inadequate for obtaining diagnostic information. This study explored the role of pulse sequence in the degradation of the nongated cardiac image. Images of diagnostic quality were obtained by using single spin-echo sequences with a very short echo time (10-20 msec TE) on a 0.12-T developmental MR unit. Marked degradation of the image was noted with longer TEs, and it is concluded that the previous unfavorable reports using a nongated technique may have been due to the longer TEs used in other units. Short-TE technique was used to examine 34 patients with a variety of cardiac diseases. Eleven patients had ventricular aneurysms. These cases showed thinning of the myocardium, and four of them showed increased signal within the aneurysm, perhaps related to regionally slower blood flow. Twenty patients had enlargement of one or more cardiac chambers. Three of these patients had thrombus within an enlarged chamber, which was readily identified on MRI. Twelve patients had left ventricular hypertrophy that was concentric in 11. One patient demonstrated asymmetric septal hypertrophy. All four pericardial effusions were low in signal intensity, but this was related to the pulse sequence used. Six patients had extrinsic masses displacing the heart and distorting the chamber contour. One patient showed intracardiac invasion of tumor; this finding was not evident on the CT. One patient with ventricular septal defect (VSD) and corrected transposition was scanned. In addition to identifying the VSD and chamber hypertrophy, the malposition of the great vessels at the base of the heart was seen. Four postoperative patients were scanned; wire suture artifact did not preclude imaging. In conclusion, diagnostic information can be obtained from nongated cardiac images provided that the TE is very short (10-20 msec). Although quantitative functional data are not available from nongated images, qualitative and diagnostic information is possible and may suffice in certain circumstances.

Cardiomegaly↗