Optimization of imaging parameters for SPECT scans of [99mTc]TRODAT-1 using Taguchi analysis

Applying Taguchi Methodology to Optimize the Brain Image Quality of 128-Sliced CT: A Feasibility Study

Injuries due to traffic accidents have been significant causes of death in Taiwan and traffic accidents have been most common in recent years. Brain computed tomography (CT) examinations can improve imaging quality and increase the value of an imaging diagnosis. The image quality of the brain gray/white matter was optimized using the Taguchi design with an indigenous polymethylmethacrylate (PMMA) slit gauge to imitate the adult brain and solid water phantoms. The two gauges without coating contrast media were located inside the center of a plate to simulate the brain and scanned to obtain images for further analysis. Five major parameters—CT slice thickness, milliampere-seconds, current voltage, filter type, and field of view—were optimized. Analysis of variance was used to determine individual interactions among all control parameters. The optimal experimental acquisition/settings were: slice thickness 2.5 mm, 300 mAs, 140 kVp, smooth filter, and FOV 200 mm2. Signal-to-noise was improved by 106% (p < 0.001) over a routine examination. The effective dose (HE) is approximately 1.33 mSv. Further clinical verification and the image quality of the ACR 464 head phantom is also discussed.

Gaussian Filter for Brain SPECT Imaging

Background. The presence of a noise component on 3D images of single-photon emission computed tomo­graphy (SPECT) of a brain significantly distorts the probability distribution function (PD) of the radioactive count rate in the images. The presence of noise and further filtering of the data, based on a subjective assessment of image quality, have a significant impact on the calculation of volumetric cerebral blood flow and the values of the uptake asymmetry of the radiopharmaceutical in a brain. Objective. We are aimed to develop a method for optimal SPECT filtering of brain images with lipophilic radiopharmaceuticals, based on a Gaussian filter (GF), for subsequent image segmentation by the threshold method.  Methods. SPECT images of the water phantom and the brain of patients with 99mTc-HMPAO were used. We have developed a technique for artificial addition of speckle noise to conditionally flawless data in order to determine the optimal parameters for smoothing SPECT, based on a GF. The quantitative criterion for optimal smoothing was the standard deviation between the PD of radioactive count rate of the smoothed image and conditionally ideal one. Results. It was shown that the maximum radioactive count rate of the SPECT image has an extremum by changing the standard deviation of the GF in the range of 0.3–0.4 pixels. The greater the noise component in the SPECT image, the more quasi-linearly the corresponding rate changes. This dependence allows determining the optimal smoothing parameters. The application of the developed smoothing technique allows restoring the probability distribution function of the radioactive count rate (distribution histogram) with an accuracy up to 5–10%. This provides the possibility to standardize SPECT images of brain. Conclusions. The research results of work solve a specific applied problem: restoration of the histogram of a radiopharmaceuticals distribution in a brain for correct quantitative assessment of regional cerebral blood flow. In contrast to the well-known publications on the filtration of SPECT data, the work takes into account that the initial tomographic data are 3D, rather than 2D slices, and contain not only uniform random Gaussian noise, but also a pronounced speckle component.

Optimizing cardiac CT angiography minimum detectable difference via Taguchi’s dynamic algorithm, a V-shaped line gauge, and three PMMA phantoms

BACKGROUND: Radiologists widely use the minimum detectable difference (MDD) concept for inspecting the imaging quality and quantify the spatial resolution of scans. OBJECTIVE: This study adopted Taguchi’s dynamic algorithm to optimize the MDD of cardiac CT angiography (CTA) using a V-shaped line gauge and three PMMA phantoms (50, 70, and 90 kg). METHODS: The phantoms were customized in compliance with the ICRU-48 report, whereas the V-shaped line gauge was indigenous to solidify the cardiac CTA scan image quality by two adjacent peaks along the V-shaped slit. Accordingly, the six factors A-F assigned in this study were A (kVp), B (mAs), C (CT pitch), D (FOV), E (iDose), and F (reconstruction filter). Since each factor could have two or three levels, eighteen groups of factor combinations were organized according to Taguchi’s dynamic algorithm. Three welltrained radiologists ranked the CTA scan images three times for three different phantoms. Thus, 27 (3 × 3 × 3) ranked scores were summed and averaged to imply the integrated performance of one specific group, and eventually, 18 groups of CTA scan images were analyzed. The unique signal-to-noise ratio (S/N, dB) and sensitivity in the dynamic algorithm were calculated to reveal the true contribution of assigned factors and clarify the situation in routine CTA diagnosis. RESULTS: Minimizing the cross-interactions among factors, the optimal factor combination was found to be as follows: A (100 kVp), B (600 mAs), C (pitch 0.200 mm), D (FOV 280 mm), E (iDose 5), and F (filter XCA). The respective MDD values were 2.15, 2.32, and 1.87 mm for 50, 70, and 90 kg phantoms, respectively. The MDD of the 90 kg phantom had the most precise spatial resolution, while that of the 70 kg phantom was the worst. CONCLUSION: The Taguchi static and dynamic optimization algorithms were compared, and the latter’s superiority was substantiated.

MINIMUM DETECTABLE DIFFERENCE OF CT ANGIOGRAPHY SCANS AT VARIOUS CARDIAC BEATS: EVALUATION VIA A CUSTOMIZED OBLIQUE V-SHAPED LINE GAUGE AND PMMA PHANTOM

The minimum detectable difference (MDD) at various beats/min (BPM) of CT angiography (CTA) was evaluated using an oblique V-shape line gauge and poly methyl methacrylate (PMMA) phantom in this study. The customized phantom with the size of [Formula: see text][Formula: see text]cm3 was made from a 1[Formula: see text]cm-thick PMMA. The reciprocating mechanism in the phantom was run by a step motor with an eccentric gear connected to a crank rod to provide a stable harmonic motion, simulating the cardiac beats. The MDD has a unique feature in defining the quality characteristic of CT-scanned images and provides more information than simple line pair/cm in the previous studies. The derived MDD was quantified according to various BPM, and the CTA factor combination was preset following either the conventional recommendation or the optimal one. In doing so, the performance was substantiated by the Taguchi-based signal-to-noise ratio and integrated by another index, namely, figure of merit (FOM). The MDD and corresponding [Formula: see text] (dB) changed from [Formula: see text][Formula: see text]mm to [Formula: see text][Formula: see text]mm and from 16.7[Formula: see text]dB to 14.2[Formula: see text]dB, respectively, for conventional settings; while those obtained for the optimal preset changed from [Formula: see text][Formula: see text]mm to [Formula: see text][Formula: see text]mm and from 12.2 dB to 16.4 dB, respectively of CTA at 0–90 BPM. The integrated FOM values for conventional or optimal cases were 1240 and 1337, respectively. The MDD proved to be a useful technique in justifying the CTA-scanned images. For compliance with previous studies, MDD results can be converted to the line pair/cm results, but it is more informative than the quantized number of line pairs.

OPTIMIZING THE TLD-100H READOUT SYSTEM UNDER VARIOUS RADIOACTIVE I-131 DOSES VIA THE REVISED TAGUCHI DYNAMIC QUALITY LOSS FUNCTION

The TLD-100H readout system performance under various radioactive I-131 exposure doses was optimized by four key factors via the revised Taguchi dynamic quality loss function. Taguchi dynamic analysis and the orthogonal array reorganizing the essential factors are crucial for the optimization of the thermoluminescent dosimeter (TLD) readout system given strict criteria of multiple irradiated environments and long-term exposure for calibrated TLDs. Accordingly, 96 TLD-100H chips were selected and randomly categorized into three batches with eight groups (four TLD chips in each group). Four factors, namely (1) initial temperature, (2) heating rate, (3) maximal temperature, and (4) TLD preheat time before reading were organized into eight combinations according to Taguchi suggestion, whereas each factor was preset at two levels. All 96 [Formula: see text] chips were put in three concentric circles with 30, 60, and 90 cm radii for 48 h, surrounding the radioactive 150[Formula: see text]mCi ([Formula: see text][Formula: see text]MBq) I-131 capsule and exposed to the cumulative doses of 88.2, 18.6, and 8.6[Formula: see text]mSv for the respective radii, accordingly. The TLD readings obtained from each group were analyzed to derive the sensitivity, coincidence, and reproducibility, then those were reorganized to draw four fish-bone-plots for the optimization. The optimal option for the TLD readout system implied the combination of A1 (a [Formula: see text]C initial temperature), B1 (a [Formula: see text]C/s heating rate), C1 (a [Formula: see text]C maximal temperature), and D2 (a 15[Formula: see text]s preheat time), which was further verified by the follow-up measurements. The dominant factors were A (initial temperature) and B (heating rate), whereas C (maximal temperature) and D (preheat time) were minor and provided negligible contributions to the system performance optimization.

Phase I clinical study with different doses of 99mTc-TRODAT-1 in healthy adults

OBJECTIVES

To study the pharmacokinetics, biodistribution, and injection doses of ^99mTc-TRODAT-1 in healthy adults.

METHODS

Thirty healthy individuals comprising 15 females and 15 males were randomly divided into three groups and the injection doses of ^99mTc-TRODAT-1 of group 1, 2, and 3 were 370 MBq, 740 MBq, and 1110 MBq, respectively. Assessments of subjective symptoms and tests were performed before and after injection. Blood and urine collections and whole-body planar imaging were analyzed at various time points. Bilateral brain striatal SPECT images obtained at 3.5 h PI were assessed visually and semiquantitatively.

RESULTS

No serious adverse events or deaths were observed in our study. The pharmacokinetic analysis showed that ^99mTc-TRODAT-1 was eliminated rapidly from the circulation, with just about 4% of the injected dose remaining in blood at 1 h post-injection. The mean cumulative urinary excretion over 24 h was just 2.96 ± 0.96%ID. The time-activity curve demonstrated that the radioactivity was mainly in liver and abdomen. The highest absorbed dose was in the dose-limiting organ, liver (20.88 ± 4.45 × 10^-3 mSv/MBq). The average effective dose was 5.22 ± 1.05 × 10^-3 mSv/MBq. The clarity of striatal images assessed visually in group 1 was worse than that in group 2 and 3. The semiquantitative analysis showed that there were no differences in striatum/cerebellum between the three groups (group 1: 1.77 ± 0.11, group 2: 1.62 ± 0.14, and group 3: 1.75 ± 0.20; P = 0.088).

CONCLUSIONS

^99mTc-TRODAT-1 was safe to use in humans and showed the status of dopaminergic neurons specifically and clearly. The injection dose we suggested was 740 MBq.

TAGUCHI METHOD-BASED OPTIMIZATION OF THE MINIMUM DETECTABLE DIFFERENCE OF A CARDIAC X-RAY IMAGING SYSTEM USING A PRECISE LINE PAIR GAUGE

Objective: To optimize the minimum detectable difference (MDD) of a cardiac X-ray imaging system using the Taguchi L8(27) analysis and a precise line pair (LP) gauge. Methods: The optimal combination of the four critical factors of the cardiac X-ray imaging system, namely X-ray focus, kilovoltage (kVp), milliamper-seconds (mAs) and source image distance (SID), providing the MDD was calculated via the Taguchi analysis and experimentally verified. Two (low and high) levels were assigned for each factor, and eight combinations of four factors were used to acquire instant X-ray images using an NDT commercial LP gauge (with a gauge length of 64[Formula: see text]mm and a width of [Formula: see text][Formula: see text]mm). The latter had five lines and was split gradually from top to bottom for the inspection of X-ray images, whose quality was ranked by three well-trained radiologists according to the double-blind criterion. The ranking grade was given by sharp contrast, low noise and precision to distinguish the LP. Accordingly, the MDD was derived to represent the spatial resolution of instant X-ray images by the revised Student’s [Formula: see text]-test analysis. The optimal combination of factors was experimentally identified and clinically verified in the follow-up inspections. Results: For the conventional setting, Group No. 7 (which obtained the highest grade among eight groups) and the optimal setting, the obtained MDD values were [Formula: see text], [Formula: see text] and [Formula: see text][Formula: see text]mm, respectively, while the LP (line pair/mm) interpolated from the gauge scale amounted to [Formula: see text], [Formula: see text] and [Formula: see text][Formula: see text]LP/mm, respectively. Conclusion: The Taguchi L8 analysis was proved to be instrumental in optimizing the cardiac X-ray imaging system MDD and is recommended to be used jointly with the revised Student’s [Formula: see text]-test analysis for improving the spatial resolution of instant X-ray images.

Degree of dopaminergic degeneration measured by 99mTc-TRODAT-1 SPECT/CT imaging

To prevent and treat Parkinson’s disease in its early stages, it is essential to be able to detect the degree of early dopaminergic neuron degeneration. Dopamine transporters (DAT) in the striatum regulate synaptic dopamine levels, and striatal ^99mTc-TRODAT-1 single-photon emission computed tomography (-SPECT) imaging is a marker for presynaptic neuronal degeneration. However, the association between the degree of dopaminergic degeneration and in vivo^99mTc-TRODAT-1 SPECT imaging is unknown. Therefore, this study investigated the association between the degree of 6-hydroxydopamine (6-OHDA)-induced dopaminergic degeneration and DAT imaging using ^99mTc-TRODAT-1 SPECT in rats. Different degrees of nigrostriatal dopamine depletion were generated by injecting different doses of 6-OHDA (2, 4, and 8 μg) into the right medial forebrain bundle. The degree of nigrostriatal dopaminergic neuron degeneration was assessed by rotational behavior and immunohistochemical staining. The results showed that striatal ^99mTc-TRODAT-1 binding was significantly diminished both in the ipsilateral and the contralateral sides in the 4 and 8 μg 6-OHDA groups, and that DAT ^99mTc-TRODAT-1 binding in the ipsilateral striatum showed a high correlation to apomorphine-induced rotations at 8 weeks post-lesion (r = –0.887, P < 0.01). There were significant correlations between DAT ^99mTc-TRODAT-1 binding in the ipsilateral striatum and the amount of tyrosine hydroxylase immunoreactive neurons in the ipsilateral substantia nigra in the 2, 4, and 8 μg 6-OHDA groups at 8 weeks post-lesion (r = 0.899, P < 0.01). These findings indicate that striatal DAT imaging using ^99mTc-TRODAT-1 is a useful technique for evaluating the severity of dopaminergic degeneration.