A method has been described to optimize the cutoff frequency of the Butterworth filter for brain SPECT imaging. Since a computer simulation study has demonstrated that separation between an object signal and the random noise in projection images in a spatial-frequency domain is influenced by the total number of counts, the cutoff frequency of the Butterworth filter should be optimized for individual subjects according to total counts in a study. To reveal the relationship between the optimal cutoff frequencies and total counts in brain SPECT study, we used a normal volunteer and 99mTc hexamethyl-propyleneamine oxime (HMPAO) to obtain projection sets with different total counts. High quality images were created from a projection set with an acquisition time of 300-seconds per projection. The filter was optimized by calculating mean square errors from high quality images visually inspecting filtered reconstructed images. Dependence between total counts and optimal cutoff frequencies was clearly demonstrated in a nonogram. Using this nomogram, the optimal cutoff frequency for each study can be estimated from total counts, maximizing visual image quality. The results suggest that the cutoff frequency of Butterworth filter should be determined by referring to total counts in each study.
Tl-201 SPECT was performed on 12 patients with nasopharyngeal carcinoma (NPC) by means of a three-head rotating gamma camera to evaluate whether or not Tl-201 SPECT was useful and reliable for assessing the tumor viability of NPC. Tl-201 clearly accumulated in the tumor in 3 patients before radiation treatment and increased Tl-201 uptake by the lesion ceased after the treatment. Three of 9 patients who were followed up after radiotherapy developed apparent local recurrence and Tl-201 SPECT clearly visualized these recurrent lesions. Tl-201 SPECT was very useful for assessing the tumor response to irradiation and for detecting local recurrent tumor. A high resolution SPECT system employing Tl-201 chloride is a new reliable and accurate diagnostic tool for the assessment of NPC.
Whether a patient with head and neck cancer has mandibular invasion or not is important in determining the method of resection surgery. But, no modality is adequately reliable when used alone in the evaluation of mandibular invasion. Therefore, to more accurately diagnose mandibular invasion in head and neck cancer, we used a new modality, namely, 99mTc methylene diphosphonate (MDP) or 99mTc hydroxymethylene diphosphonate (HMDP) and 201Tl chloride dual isotope single photon emission computed tomography (Tc/Tl SPECT). The aim of this study is to disclose the usefulness of Tc/Tl SPECT in the assessment of mandibular invasion by head and neck cancers. 99mTc-MDP or -HMDP SPECT (Tc SPECT)s and 201Tl chloride SPECT (Tl SPECT)s were performed in 34 patients with suspected mandibular involvement of head and neck cancer. Thirty of 34 cases underwent both TcMTl SPECT and CT examination. Tc/Tl SPECT fusion images were obtained using the Automatic Registration Tool (ART, TOSHIBA, Japan) system. In the diagnosis of mandibular invasion on Tc/Tl SPECT fusion images, a problem was that the range of Tc and Tl uptake was changed by the condition of display used in the reconstruction and expression of the images. Then, prior to clinical evaluation, to reveal the most appropriate upper window level for display, a phantom study was performed. In a clinical study, the upper window level was set at 40 or 50%, which were verified to be the proper values in the preliminary study. The diagnostic accuracy obtained using Tc SPECT, TcMTl SPECT and CT was compared with the histopathological findings. Tc/Tl SPECT at 40 and 50% upper window level had higher specificity, accuracy, and positive predictive value (73.3%, 85.3%, 81.8%) than Tc SPECT alone (21.4%, 67.6%, 64.5%) and higher sensitivity and negative predictive value (94.7%, 91.7%) than CT (70.6%, 72.2%) for detecting mandibular invasion. Tc/Tl SPECT was a useful diagnostic procedure for the assessment of mandibular invasion by head and neck cancers.
Identification of the sentinel lymph nodes in patients with breast cancer is often hampered by high radioactivity from the injection site, since the distance between the injection site and regional lymph nodes is quite short in these patients. We investigated the usefulness of the modified oblique view of the axilla (MOVA) method introduced by Haigh et al., aiming at better discrimination of the target and higher resolution. Compared with the standard anterior view (SAV) of the supine position and conventional oblique view (COV) imaging, MOVA was able to obtain a longer distance between the injection site and axillary lymph nodes in 20 of 21 lymph nodes. MOVA provided more effective information for visual evaluation of the geometry of axillary lymph nodes in half the cases, and one lymph node was detected only with MOVA. In contrast, SAV provided better imaging in one patient. Although our results support the usefulness of MOVA, the combined application of MOVA and SAV is desirable, since sentinel lymph node detection with the gamma-probe is performed in the supine position during surgery.
Submicrometer transistor gates have been fabricated in CMOS/SOS prototype VLSI circuits and GaAs digital integrated circuits. A hybrid lithography approach was used to take advantage of the rapid throughput of optical lithography and the high resolution capabilities of electron-beam lithography. The entire gate levels of these devices were defined with direct write electron-beam lithography. The six remaining lithographies in the CMOS/SOS device and the five remaining levels in the GaAs device were defined with various optical lithography systems. A unique electron-beam fiducial marker fabrication technique was required for each of the two devices. The goal of this approach was to substitute electron-beam lithography for optical lithography in the gate level only, leaving the remaining device process unaltered. Gate lengths as small as 0.6 μm were fabricated in the Si devices and 0.9 μm gates were achieved in GaAs. The CMOS/SOS gates were patterned in PMMA resist over MoSi2 and requires an Al liftoff and ion mill. The GaAs gates were patterned in AZ2400 resist which became an etch mask for underlying SiO2 and Si3N4 films. Circuits in both devices were sucessfully operated.
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