An optimized collimator for single-photon computed tomography with a scintillation camera.

The problem of nonuniform response, which is inherent in scintillationcamera emission computed tomography, can be minimized by proper collimator design. A specially fabricated collimator, optimized for emission computed tomography, was designed. This collimator has a calculated full width at half maximum of 1 cm at 15 cm in front of the collimator. When this collimator is used in conjunction with averaged opposed views, excellent uniformity across the reconstruction plane is achievable.

The Humongotron--a scintillation-camera transaxial tomograph.

An emission transaxial tomographic system using a scintillation camera as the detector is described. The unit allows accurate positioning of a scintillation camera's detector at any angle around a patient in order to obtain the multiple projection images needed for transaxial tomography, and it is capable of imaging any area of the body. The camera can also be used for all types of conventional imaging procedures. Image processing is performed by a small on-line computer. A convolution algorithm and a mathematical technique for approximate absorption correction are used to obtain high-resolution and high-contrast images with good quantitative accuracy. The operation of the system is described and representative phantom and patient studies are presented to illustrate the capabilities of the system.

Facial bone scanning by emission tomography.

A single-photon emission tomographic system was used to study the normal anatomy of the facial bones and the usefulness of emission computed tomography in evaluating diseases of the bones of the face. The examination was performed following routine bone scintigraphy and took an additional 20-30 min. The anatomy of the facial bones was well defined, with clear separation of deep and superficial structures. Early experience with tumor, infection, bone grafts, and postirradiation osteonecrosis indicates that useful added diagnositc information can be obtained by this method.

Coded-aperture imaging of the heart.

Coded-aperture imaging of the heart combines the advantages of tomography with good sensitivity, high resolution, and accurate size scaling. Since the images are multiplexed, the method may be adapted to small, portable cameras for bed-side use without sacrificing image resolution. A new coded aperture designed especially for cardiac imaging has been constructed and tested. This aperture incorporates significant improvements over previous designs. Longitudinal tomograms are calculated at 1-cm intervals using a modified ART algorithm. Experimental lateral resulution at 140 keV with a portable scintillation camera is 3.8 mm FWHM at 4 cm, and 7.8 mm FWHM at 12 cm. Dpth resolution determined from a sloping line source is 1.1 cm FWHM at 4 cm, and 2.9 cm at 12 cm. The calculated point-source sensitivities in air at 4 cm and 12 cm, respectively, are 20 and 8 cps/microCi. Images of good diagnostic quality have been obtained in phantoms and in a dog model of acute myocardial infarction, using thallium-201, technetium-99m pyrophosphate, and gated ventricular blood-pool imaging with Tc-labeled red blood cells. Preliminary studies in humans confirm the good results in animals.

Calculation of viable and infarcted myocardial mass from thallium-201 tomograms.

The feasibility of determining the mass of both viable and infarcted myocardium from tomographic images of thallium-201 distribution in the heart was studied in two normal dogs and ten dogs with acute infarction. Twenty-four hours after occlusion, thallium-201 was injected and 10 min later the hearts were removed and transaxial emission computed tomograms were obtained. Using the computer, an operator defined the epi- and endocardial surfaces of the left ventricle and the area of infarction in each tomogram. The computer then calculated values for total left-ventricular mass (TLVM) infarcted mass (IM) and the percentage of the left ventricle infarcted (% LVI). The calculated values were compared with measured weights, and good correlation was found between them: for TLVM, r = 0.87; for IM, r = 0.90; and for %LVI, r = 0.87. Good interobserver and intra-observer correlations were also found. Thallium-201 emission computed tomography offers a potential means to measure both myocardial mass and acute myocardial injury.

Monitoring and analysis of oxygenation and ventilation during rigid bronchoscopic neodymium-YAG laser resection of airway tumors.

Neodymium-YAG (yttrium-aluminum-garnet) laser resection of obstructing and inoperable tumors of the large airways is used as palliative therapy to improve the quality of survival in patients by alleviating airway obstruction. Rapid changes in oxygenation and ventilation can occur during these procedures. In a study of 14 patients, transcutaneous oxygen (PtcO2) and carbon dioxide (PtcCO2) monitors responded slowly to these changes and frequently provided misleading values. Pulse oximetry (SNO2) accurately reflected arterial oxygen saturation but did not indicate severe desaturation until arterial oxygen tension approached dangerously low values. Thus, we did not find PtcO2 or PtcCO2 monitoring to be clinically useful during neodymium-YAG laser resection of airway tumors through a rigid bronchoscope. SNO2 was clinically useful and accurate; however, a large decrement in oxygenation may occur before changes in oxygen saturation ensue and are detected.

Bronchoplastic procedures in the treatment of carcinoid tumors of the tracheobronchial tree.

Sixteen patients, aged 10 to 70 years, had carcinoid tumors of the lower respiratory tract treated by various resective tracheobronchoplastic procedures. These represent 8.8 percent of 181 patients with carcinoid lesions treated during a recent 20 year period. All 16 patients had respiratory symptoms, and one patient also had the carcinoid syndrome. Roentgenographic changes ranged from a mass or atelectasis (or both) through unilateral lung hyperinflation to clear lungs with subtle filling defects in major airways. All tumors were visualized endoscopically, and 13 patients had biopsies. Histopathologically, all tumors were "typical" carcinoids . Before operation, the patients had minimal or no respiratory insufficiency, although flow-volume and ventilation-perfusion abnormalities were noted when major airways were affected. Surgical management at thoracotomy was as follows: (1) simple wedge tracheobronchotomy without lung resection (five patients); (2) bronchial sleeve resection without lung resection (three patients); and (3) bronchial sleeve with upper lobe resection (eight patients). These 16 operations were performed with eight technical anatomic variations. No early or late deaths occurred. One patient had early transient atelectasis, and three patients required late endoscopic removal of suture granulation tissue. All patients were alive without recurrence of tumor or carcinoid syndrome or other respiratory complications 6 months to 19 years postoperatively. Pulmonary resection should be avoided unless there is histologic evidence of tumor extension into lung parenchyma or irreversible pulmonary suppuration distal to the obstructive tumor.

The lower limits of flammability of halothane, enflurane, and isoflurane.

Halothane, enflurane, and isoflurane, generally regarded as nonflammable, can be ignited under laboratory conditions. Attainment of similar conditions during clinical anesthesia is most unlikely. Nevertheless, early in the course of anesthesia while the concentration of the agent is still high, electrosurgery is best avoided if nitrous oxide is part of the anesthetic mixture and the operative field is exposed directly to the inflowing gases (as during certain laryngeal procedures).

Myocardial infarct quantification in the dog by single photon emission computed tomography.

Radionuclide techniques for sizing acute myocardial infarction have been hampered by the intrinsic limitations of the scintillation camera. Emission computed tomography can overcome these limitations. Single photon emission computed tomograms of the distribution of technetium-99m pyrophosphate in acute anterior and posterior infarcts were obtained in 16 dogs after death. Tomograms were also obtained in 10 dogs during life without gating. The size of the infarcts was determined by staining gross sections of the heart with nitro blue tetrazolium, dissecting out the infarcted tissue and weighing it. Infarct sizes were determined from the tomographic images and compared with the measured infarct sizes. Good images showing the location and three-dimensional extent of the infarcts were obtained in all dogs. The measured and calculated infarct sizes correlated well (r = 0.85). Comparison of the calculated sizes in the living (non-gated) and dead ("physiologically" gated) animals showed reasonable agreement (r = 0.87). Single photon emission computed tomography is a feasible and useful technique for localizing and sizing acute myocardial infarctions.

Myocardial imaging using emission computed tomography.

Single-photon emission computed tomography (ECT) was evaluated during myocardial studies in dogs. Acute anterior and posterior infarcts were imaged following injection of 99mTc-pyrophosphate or 201Tl. In most cases, tomographic delineation of infarct location and extent correlated with tissue section. The 99mTc images were far superior to the 201Tl images. ECT improves delineation of tracer within the myocardium.