William H. McCartney

Quantitative cardiac SPECT reconstruction with reduced image degradation due to patient anatomy

Patient anatomy has complicated effects on cardiac SPECT images. The authors investigated reconstruction methods which substantially reduced these effects for improved image quality. A 3D mathematical cardiac-torso (MCAT) phantom which models the anatomical structures in the thorax region were used in the study. The phantom was modified to simulate variations in patient anatomy including regions of natural thinning along the myocardium, body size, diaphragmatic shape, gender, and size and shape of breasts for female patients. Distributions of attenuation coefficients and Tl-201 uptake in different organs in a normal patient were also simulated. Emission projection data were generated from the phantoms including effects of attenuation and detector response. The authors have observed the attenuation-induced artifacts caused by patient anatomy in the conventional FBP reconstructed images. Accurate attenuation compensation using iterative reconstruction algorithms and attenuation maps substantially reduced the image artifacts and improved quantitative accuracy. The authors conclude that reconstruction methods which accurately compensate for nonuniform attenuation can substantially reduce image degradation caused by variations in patient anatomy in cardiac SPECT. >

The importance and implementation of accurate 3D compensation methods for quantitative SPECT

The purpose of this study was to investigate the importance of 2D versus 3D compensation methods in SPECT. The compensation methods included in the study addressed two important degrading factors, namely attenuating and collimator-detector response in SPET. They can be divided into two general categories. The conventional methods are based on the filtered backprojection algorithm, the Chang algorithm for attenuation compensation and the Metz filter for detector response compensation. These methods, which were computationally efficient, could only achieve approximate compensation due to the assumptions made. The quantitative compensation methods provide accurate compensation by modelling the degrading effects at the expense of large computational requirements. Both types of compensation methods were implemented in 2D and 3D reconstructions. The 2D and 3D reconstruction/compensation methods were evaluated using data from simulation of brain and heart, and patient thallium SPECT studies. Our results demonstrate the importance of compensation methods in improving the quality and quantitative accuracy of SPECT images and the relative effectiveness of the different 2D and 3D reconstruction/compensation methods. We concluded that 3D implementation of the quantitative compensation methods provides the best SPECT image in terms of quantitative accuracy, spatial resolution, and noise at a cost of high computational requirements.

The role of noninvasive tests versus pulmonary angiography in the diagnosis of pulmonary embolism

We studied 243 patients in whom 248 pulmonary angiograms were performed because of suspected pulmonary embolism. Ventilation and perfusion lung scanning in 140 of them revealed 38 to be in low and high probability groups. Of 19 patients with subsegmental and nonsegmental perfusion defects that were matched with ventilation defects, none had pulmonary embolism. Conversely, angiography was positive in 17 of 19 patients with multiple segmental or lobar perfusion defects in areas of normal ventilation. Doppler flow examinations of the veins of the legs showed normal flow in 61 of 79 (77 percent) patients with pulmonary emboli and, therefore, were insensitive indicators of embolism. There was no mortality from angiography, and serious complications occurred in 2 percent of the patients. Anticoagulation in 83 patients was associated with bleeding in 25, two of whom died. The data indicate that ventilation-perfusion lung scanning can be used to separate many of the patients suspected of having pulmonary embolism who need anticoagulant treatment from those who do not. However, there is a considerable number of patients with nonspecific abnormalities on lung scan. For this group of patients with nonspecific abnormalities, the risk of complications from empiric treatment with anticoagulant drugs is probably greater than the risk of complications from pulmonary angiography. Further, our data show that patients with negative angiography have a very low risk of subsequent pulmonary embolism. In this group of patients, therefore, pulmonary embolism should be demonstrated by angiography before long-term anticoagulant therapy is prescribed.

Role of gallium 67 in inflammatory disease.

Gallium 67 has been found to be extremely useful for detection of inflammatory disease. In the skeletal system it complements the 99m Tc-phosphate compounds in differentiating periatricular osteomyelitis, septic arthritis, and cellulitis. Gallium is particularly useful in documenting successful treatment of bone infection because the phosphate scan remains positive for much longer periods of time. In a variety of chest disorders gallium uptake has been found to correlate well with the active inflammatory state. One of the most frequent uses of gallium imaging has been for localization of inflammatory foci in postoperative patients as well as in patients who present with fever of undetermined origin. Neutrophilic labeling followed by migration to the inflammatory area appears to be the major mechanism of localization of radiogallium. For this reason leukopenic patients constitute a group in which false negative results may be encountered.

Quantitative single-photon emission computed tomography: Basic and clinical considerations

Although quantitative single-photon emission computed tomography (SPECT) has been the goal of much research effort for a number of years, only recently has it received wide interest, especially for clinical applications. It has been increasingly recognized that the achievement of quantitative SPECT will increase the accuracy of measurements, such as dimensions of specific regions of interest, absolute amount of radioactivity, and dosimetry calculations, and substantially reduce reconstruction image artifacts and distortions, thus, greatly improving clinical diagnosis. This article provides a review of the definition of terms, major factors affecting SPECT quantitation and their degrading effects on SPECT image quality, and methods to compensate for these effects. Compensation methods include those that make certain approximations for ease of implementation and those that provide more accurate compensation by modeling the imaging process more exactly, usually at the cost of increased complexity and computational requirements. Different reconstruction and compensation methods may be compared through the use of phantom cardiac and brain SPECT studies. The clinical efficacy of the methods may be demonstrated by applying them to a clinical thallium-201 myocardial perfusion SPECT study. The results clearly demonstrate that, by modeling the imaging process and/or image degrading factors three-dimensionally, quantitative reconstruction and compensation methods provide the best image quality and quantitative accuracy. Important research efforts and developmental work being conducted currently to bring quantitative SPECT into routine clinical use are also discussed.

Treatment of calcinosis universalis with low-dose warfarin

Patients with calcinosis universalis secondary to dermatomyositis or systemic sclerosis have increased levels of the calcium-binding amino acid, gamma-carboxyglutamic acid. The enzyme that effects gamma carboxylation of glutamic acid is warfarin-sensitive. Four patients with calcinosis universalis were treated with 1 mg per day of warfarin for 18 months in a non-blind initial study. Two patients had both decreased gamma-carboxyglutamic acid urinary concentration and decreased extra-skeletal uptake on technetium 99m-diphosphonate whole-body nuclear scanning. In a subsequent double-blind placebo study, two thirds of the patients receiving 1 mg per day of warfarin had decreases in extra-skeletal nuclear tracer uptake after 18 months, compared with none of the four patients receiving placebo. No patient had a change in clinical assessment, bleeding complication, or baseline normal prothrombin time. This low-dose warfarin regimen appears to have no demonstrable adverse effects, and these results suggest a beneficial effect on the progression of calcinosis in these rheumatic diseases.

Psychophysical responses to a speech stressor: Correlation of plasma beta-endorphin levels at rest and after psychological stress with thermally measured pain threshold in patients with coronary artery disease

OBJECTIVES We tested the hypothesis that psychological stress alters plasma levels of opioid peptides and that these plasma levels are related to pain perception in patients with coronary artery disease. BACKGROUND Public speaking psychological stress has previously been shown to be associated with silent ischemia. METHODS After instrumentation and a 30-min rest period, venous blood samples for beta-endorphin were obtained before and immediately after psychological stress in 20 patients with coronary artery disease. Pain threshold was then assessed using a thermal probe technique at baseline and immediately after stress. Patients gave three brief speeches lasting a total of 15 min about real-life hassle situations. RESULTS Psychological stress significantly increases plasma beta-endorphin levels (4.3 +/- 0.9 pmol/liter [mean +/- SE] at rest to 8.3 +/- 2 pmol/liter after stress, p < 0.05). There was a significant positive correlation between pain threshold and beta-endorphin levels after stress (r = 0.577, p = 0.008). This significant positive correlation was still present while rest blood pressure and change in blood pressure during stress were controlled for by analysis of covariance techniques. CONCLUSIONS In patients with coronary artery disease and exercise-induced ischemia, public speaking produces psychological stress manifested by increased cardiovascular reactivity and causes an increase in plasma beta-endorphin levels that is significantly correlated with pain thresholds. These findings may explain the predominance of silent ischemia during psychological stress in patients with coronary artery disease.

Quantitative myocardial perfusion SPECT

In recent years, there has been much interest in the clinical application of attenuation compensation to myocardial perfusion single photon emission computed tomography (SPECT) with the promise that accurate quantitative images can be obtained to improve clinical diagnoses. The different attenuation compensation methods that are available create confusion and some misconceptions. Also, attenuation-compensated images reveal other image-degrading effects including collimator-detector blurring and scatter that are not apparent in uncompensated images. This article presents basic concepts of the major factors that degrade the quality and quantitative accuracy of myocardial perfusion SPECT images, and includes a discussion of the various image reconstruction and compensation methods and misconceptions and pitfalls in implementation. The differences between the various compensation methods and their performance are demonstrated. Particular emphasis is directed to an approach that promises to provide quantititve myocardial perfusion SPECT images by accurately compensating for the 3-dimensional (3-D) attenuation, collimator-detector response, and scatter effects. With advances in the computer hardware and optimized implementation techniques, quantitatively accurate and highquality myocardial perfusion SPECT images can be obtained in clinically acceptable processing time. Examples from simulation, phantom, and patient studies are used to demonstrate the various aspects of the investigation. We conclude that quantitative myocardial perfusion SPECT, which holds great promise to improve clinical diagnosis, is an achievable goal in the near future.

The Value of Carcinoembryonic Antigen (CEA) as an Adjunct to the Radiological Colon Examination in the Diagnosis of Malignancy

The relative value of the carcinoembryonic antigen immunoassay was assessed as an adjunct to the radiological colon examination in the diagnosis of carcinoma. The serum CEA examination was less specific and accurate than the colon examination in diagnosing new cases of primary colonic malignancy; however, when the two studies were combined, the percentage of cases detected increased from approximately 65% and 90%, respectively, to approximately 95%. The CEA assay was superior in detecting recurrence or metastasis in patients with prior resection for colon carcinoma. Once again, the combined detection rate of the two examinations was better than that of either individual procedure.

Computerized tomography applied to gynecologic oncology

Forty patients on the gynecologic oncology service at the University of North Carolina were evaluated with CT scans. Accuracy and clinical benefit of these scans were compared to those of manual clinical examinations. The CT scans were generally superior and had fewer (9) verified errors in the regions of the pelvic wall and para-aortic area than did the manual examinations (17). Both the CT and bimanual examinations had the same number of verified errors (3) in the central pelvic region. The authors found the CT scans to be beneficial in evaluation of pelvic wall and para-aortic regions for treatment planning of either primary or recurrent cancer.