Mark W. Groch

A new heart-sounds gating device for medical imaging

A heart-sounds gating device has been designed and tested which identifies, individually, both the first (S1) and second (S2) heart sound from their timing relationship, providing two trigger points through the cardiac cycle for synchronizing medical images. The gate utilizes dynamically varying timing windows to anticipate the occurrence of S1 and S2. It has been initially applied to nuclear imaging of the cardiac bloodpool, but may be applied to any imaging modality requiring cardiac synchronization.<<ETX>>

An MRI tissue equivalent lesion phantom using a novel polysaccharide material

A new polysaccharide material, TX-150, and method is described which will potentially allow formation of stable, multi-compartment MRI phantoms constructed without intervening septa. TX-150 can be made into water based gels which are nominally tissue equivalent. Although contiguous regions of different water content are not possible, as water diffusion will occur until equilibrium is reached, TX-150 gel T1 and T2 values can be adjusted independently, while maintaining a constant water composition, by appropriate additives. Unlike paramagnetic ions and chelates, metal phthalocyanines have been found to bind tightly to TX-150, thus, permitting formation of stable contiguous regions of differing T1 relaxation properties. Phantom T2 values can be effectively modified with 2-2-diphenyl-1 picrylhydrazyl, which has little affect on gel T1 values, to form septumless lesion phantoms of varying T1 and T2.

Respiratory gating in magnetic resonance imaging: Improved image quality over non-gated images for equal scan time

Magnetic resonance image quality is adversely affected by respiratory (RESP) motion during the scan. Respiratory gating improves magnetic resonance image (MRI) quality and removes artifacts, but has not been widely used, as RESP gating increases scan time. Our RESP-gating device was used to study scan time versus improvement in image quality using various gating modes; with and without combined electrocardiographic (ECG) gating. When RESP scans were acquired for the same time as non-gated scans, by using a wide RESP-gating window bracketing end expiration and a reduced number of pulse sequence repetitions, substantial improvement in image quality (over non-gated scans) resulted, despite the inferior statistical content of the acquisition.

Image normalization and background subtraction in T1-201/Tc-99m parathyroid subtraction scintigraphy. Effect on lesion detection.

The authors have developed two computer algorithms for TI-201/Tc-99m parathyroid subtraction scintigraphy that was performed on patients who subsequently underwent surgical exploration of the neck. Both methods employed a region-of-interest drawn around the thyroid/parathyroid glands for image realignment. The first algorithm normalized the TI-201 and Tc-99m images using the ratio of maximum counts over the thyroid in each image. The second computer algorithm incorporated TI-201 image background correction and normalization by the average of the ratios of maximum counts computed over each quadrant in both images. In 10 patients with confirmed parathyroid adenomas or hyperplasia, the first method yielded a 44% sensitivity. Upon reanalysis with the second algorithm, the sensitivity improved to 100%. Subsequently, in a total of 22 patients with 30 abnormal glands analyzed with the second algorithm, a sensitivity of 80% (94% for adenoma and 62% for hyperplasia) was achieved, with a specificity of 91%, as confirmed by surgery.

Single Photon Emission Computed Tomography

Since the introduction of single photon emission computed tomographic (SPECT; abbreviated SPET in Europe) techniques during the 1960s,123,124 SPECT has become a routine part of virtually every nuclear medicine department. With SPECT, by moving the gamma camera or cameras around the patient and viewing the object from at least 180°, a three-dimensional (3-D) data set can be reconstructed. When this data set is reconstructed by filtered back-projection methods, the SPECT slices are viewed in the transverse, oblique, sagittal, or coronal dimensions or can be formed, by state-of-the-art systems, into a 3-D representation of the organ surface (volume “rendered”). The significance of SPECT is that out-of-plane information is removed, not simply blurred as with earlier forms of tomography in nuclear medicine and radiology.107,108,112,145

A computer method for cardiac radionuclide kymography

Abstract A technique is presented for the generation of cardiac kymograms by a minicomputer from the data collected during routine multi-image gated cardiac blood pool imaging. A radionuclide kymogram is a data processing and display technique which permits quantitative assessment of boundary motion for cyclic functions such as ventricular contraction. Multiple kymograms can be obtained without any modification of the routine patient data collection protocol. The kymograms focus the observers attention on specific segments of the cardiac chambers permitting easier extraction of quantitative information to add to these standard wall motion studies.