Two devices for longitudinal emission tomography of the thyroid.

Two devices especially designed for tomographic thyroid imaging are compared on the basis of phantom experiments and four patients studies: a seven pinhole (7P) collimator and a time-coded aperture (TCA). The results of patient studies show that the 7P collimator may miss smaller abnormalities and is prone to incorrect positioning. The TCA reconstructions of patient data confirm the good performance observed in the phantom studies and demonstrate a high degree of lesion detectability. The TCA also provides higher efficiency and shorter imaging times than the 7P collimator. It is therefore concluded that TCA imaging is a promising alternative to multiple view pinhole imaging of the thyroid.

Seven-pinhole tomography of the thyroid.

In this paper we introduce a new application of the sevenpinhole (7P) collimator: tomographic imaging of the thyroid. The collimator design has been reoptimized for this particular application by diminishing the distance from the collimator plate to the crystal and by choosing a smaller pinhole diameter. To reconstruct thyroid images from the two-dimensional projection data we use a method which we developed for 7P tomographic imaging of the heart [1]. Phantom experiments and patient studies demonstrate that this new device is capable of producing tomographic images of good quality and high resolution. Therefore, it seems to offer a promising alternative to conventional planar imaging of the thyroid (using a single-pinhole collimator).

Time-coded aperture tomography: experimental results.

In this paper, we discuss the applicability of a time-coded aperture system especially designed for thyroid tomography on the basis of phantom experiments. Our studies show that 1) the quality of the reconstructions is high (e.g., a cold spot of 6 mm diameter in a thyroid phantom can easily be detected), and 2) the reconstruction can be carried out in less than 11 min on a standard 16 bit minicomputer (HP1000). It is therefore concluded that the clinical potentiality of the device is good.

Regional distribution of ventilation assessed by Kr-81m scintigraphy employing temporal Fourier transform.

Temporal Fourier analysis was applied to Kr-81m ventilation scintigraphy to determine the amplitude (AMP1) and phase (PHA1) of the first harmonic of a single composite respiratory cycle and to compare regional patterns in subjects with obstructive pulmonary disease (COPD) and nonobstructed subjects. Six nonobstructed subjects, three subjects with small airway disease, six subjects with COPD, and one subject with restrictive disease were investigated. The mean value of the functional PHA1 image (PHA1m) correlated negatively with 1-second forced expiratory volume (FEV1) (r = -0.801, P less than .001), with %FEV1/FVC (r = -0.636, P less than .01) and maximum midexpiratory flow rate (FEF25-75%) (r = -0.723, P less than .002), and correlated positively with residual volume (r = 0.640, P less than .01). PHA1m values for the six subjects with COPD were significantly higher (t = 2.359, P less than .05) than for the ten nonobstructed subjects. Display of phase and amplitude functional images permits a visual evaluation of the regional distribution of ventilation to be made. Regional abnormalities of air flow were detected in obstructed subjects, and the presence of airway obstruction could be predicted. Dynamic ventilation imaging, therefore, appears to be a potentially useful noninvasive technique to assess lung impairment on a localized level.

Improved tomographic reconstruction in seven-pinhole imaging.

Cardiac emission tomography using a seven-pinhole collimator has received only little appreciation as a diagnostic imaging technique. The main reasons are the limited angular sampling of the seven-pinhole device and the difficulties encountered in properly positioning the patient relative to the collimator/camera system. In order to overcome these problems, we have developed a modified ART3 algorithm for reconstruction of the radioactivity distribution in the heart. The method is very appropriate for seven-pinhole tomography, as demonstrated by the quality of the reconstructions, by the excellent point source resolution of the system response, and by a comparison to two other suitable reconstruction techniques, viz., SMART and SIRT.

Three-dimensional simulation of time-coded emission tomography.

In this paper we discuss the potentialities of a time-coded single photon emissive imaging system for thyroid tomography. We have performed three-dimensional simulation studies in order to answer two questions: 1) does this coded aperture device produce good quality reconstructions, and 2) can the reconstruction be carried out sufficiently fast on a microcomputer. Our study leads to the conclusion that both questions can be answered affirmatively. Hence, time-coded emission tomography is a potentially useful imaging technique for diagnostic clinical practice.