Generative Adversarial Network-Enhanced Ultra-Low-Dose [18F]-PI-2620 τ PET/MRI in Aging and Neurodegenerative Populations

BACKGROUND AND PURPOSE

With the utility of hybrid τ PET/MR imaging in the screening, diagnosis, and follow-up of individuals with neurodegenerative diseases, we investigated whether deep learning techniques can be used in enhancing ultra-low-dose [18F]-PI-2620 τ PET/MR images to produce diagnostic-quality images.

MATERIALS AND METHODS

Forty-four healthy aging participants and patients with neurodegenerative diseases were recruited for this study, and [18F]-PI-2620 τ PET/MR data were simultaneously acquired. A generative adversarial network was trained to enhance ultra-low-dose τ images, which were reconstructed from a random sampling of 1/20 (approximately 5% of original count level) of the original full-dose data. MR images were also used as additional input channels. Region-based analyses as well as a reader study were conducted to assess the image quality of the enhanced images compared with their full-dose counterparts.

RESULTS

The enhanced ultra-low-dose τ images showed apparent noise reduction compared with the ultra-low-dose images. The regional standard uptake value ratios showed that while, in general, there is an underestimation for both image types, especially in regions with higher uptake, when focusing on the healthy-but-amyloid-positive population (with relatively lower τ uptake), this bias was reduced in the enhanced ultra-low-dose images. The radiotracer uptake patterns in the enhanced images were read accurately compared with their full-dose counterparts.

CONCLUSIONS

The clinical readings of deep learning-enhanced ultra-low-dose τ PET images were consistent with those performed with full-dose imaging, suggesting the possibility of reducing the dose and enabling more frequent examinations for dementia monitoring.

Investigating Simultaneity for Deep Learning-Enhanced Actual Ultra-Low-Dose Amyloid PET/MR Imaging

BACKGROUND AND PURPOSE

Diagnostic-quality amyloid PET images can be created with deep learning using actual ultra-low-dose PET images and simultaneous structural MR imaging. Here, we investigated whether simultaneity is required; if not, MR imaging-assisted ultra-low-dose PET imaging could be performed with separate PET/CT and MR imaging acquisitions.

MATERIALS AND METHODS

We recruited 48 participants: Thirty-two (20 women; mean, 67.7 [SD, 7.9] years) were used for pretraining; 328 (SD, 32) MBq of [¹⁸F] florbetaben was injected. Sixteen participants (6 women; mean, 71.4 [SD. 8.7] years of age) were scanned in 2 sessions, with 6.5 (SD, 3.8) and 300 (SD, 14) MBq of [¹⁸F] florbetaben injected, respectively. Structural MR imaging was acquired simultaneously with PET (90-110 minutes postinjection) on integrated PET/MR imaging in 2 sessions. Multiple U-Net-based deep networks were trained to create diagnostic PET images. For each method, training was done with the ultra-low-dose PET as input combined with MR imaging from either the ultra-low-dose session (simultaneous) or from the standard-dose PET session (nonsimultaneous). Image quality of the enhanced and ultra-low-dose PET images was evaluated using quantitative signal-processing methods, standardized uptake value ratio correlation, and clinical reads.

RESULTS

Qualitatively, the enhanced images resembled the standard-dose image for both simultaneous and nonsimultaneous conditions. Three quantitative metrics showed significant improvement for all networks and no differences due to simultaneity. Standardized uptake value ratio correlation was high across different image types and network training methods, and 31/32 enhanced image pairs were read similarly.

CONCLUSIONS

This work suggests that accurate amyloid PET images can be generated using enhanced ultra-low-dose PET and either nonsimultaneous or simultaneous MR imaging, broadening the utility of ultra-low-dose amyloid PET imaging.

A floating wide-band current source for electrical impedance tomography

The quality of reconstructed images in Electrical Impedance Tomography (EIT) depends on two essential factors: first, precision of the EIT hardware in current injection and voltage measurement and second, efficiency of its image reconstruction algorithm. Therefore the current source plays an important and a vital role in EIT instruments. Floating-load current sources constructed using sink and source drivers have better performance and higher output impedance than grounded-load (single-ended) current sources. In addition, a main feature of this kind is that the current source is not connected to the ground potential directly but via a large impedance. In this paper, we first focus on recent studies on designed EIT current sources, and after that, a practical design of a floating-load high output impedance current source-operating over a wide frequency band-will be proposed in detail. Simulation results of the proposed voltage-controlled current source (VCCS), along with some other models, will be shown and compared. At the end, the results of practical tests on the VCCS and a few EIT images, taken using our prototype EIT system coupled with the mentioned VCCS, will be illustrated which proves the quality of the proposed current source.

Memory effects on epidemic evolution: The susceptible-infected-recovered epidemic model

Memory has a great impact on the evolution of every process related to human societies. Among them, the evolution of an epidemic is directly related to the individuals' experiences. Indeed, any real epidemic process is clearly sustained by a non-Markovian dynamics: memory effects play an essential role in the spreading of diseases. Including memory effects in the susceptible-infected-recovered (SIR) epidemic model seems very appropriate for such an investigation. Thus, the memory prone SIR model dynamics is investigated using fractional derivatives. The decay of long-range memory, taken as a power-law function, is directly controlled by the order of the fractional derivatives in the corresponding nonlinear fractional differential evolution equations. Here we assume "fully mixed" approximation and show that the epidemic threshold is shifted to higher values than those for the memoryless system, depending on this memory "length" decay exponent. We also consider the SIR model on structured networks and study the effect of topology on threshold points in a non-Markovian dynamics. Furthermore, the lack of access to the precise information about the initial conditions or the past events plays a very relevant role in the correct estimation or prediction of the epidemic evolution. Such a "constraint" is analyzed and discussed.

Inhibition of human prenatal biosynthesis of all-trans-retinoic acid by ethanol, ethanol metabolites, and products of lipid peroxidation reactions: a possible role for CYP2E1

Biotransformation of all-trans-retinol (t-ROH) and all-trans-retinal (t-RAL) to all-trans-retinoic acid (t-RA) in human prenatal hepatic tissues (53-84 gestational days) was investigated with HPLC using human adult hepatic tissues as positive controls. Catalysis of the biotransformation of t-ROH by prenatal human cytosolic fractions resulted in accumulation of t-RAL with minimal t-RA. Oxidations of t-ROH catalyzed by prenatal cytosol were supported by both NAD+ and NADP+, although NAD+ was a much better cofactor. In contrast, catalysis of the oxidation of t-RAL to t-RA appeared to be solely NAD+ dependent. Substrate Km values for conversions of t-ROH to t-RAL and of t-RAL to t-RA were 82.4 and 65.8 microM, respectively. At concentrations of 10 and 90 mM, ethanol inhibited the conversion of t-ROH to t-RAL by 25 and 43%, respectively, but did not inhibit the conversion of t-RAL to t-RA significantly. In contrast, acetaldehyde reduced the conversion of t-RAL to t-RA by 25 and 87% at 0.1 and 10 mM respective concentrations. Several alcohols and aldehydes known to be generated from lipid peroxides also exhibited significant inhibition of t-RA biosynthesis in human prenatal hepatic tissues. Among the compounds tested, 4-hydroxy-2-nonenal (4-HNE) was highly effective in inhibiting the conversion of t-RAL to t-RA. A 20% inhibition was observed at a concentration of only 0.001 mM, and nearly complete inhibition was produced at 0.1 mM. Human fetal and embryonic hepatic tissues each exhibited significant CYP2E1 expression as assessed with chlorzoxazone 6-hydroxylation, a highly sensitive western blotting technique, and reverse transcriptase-polymerase chain reaction (PCR) (RT-PCR), suggesting that lipid peroxidation can be initiated via CYP2E1-catalyzed ethanol oxidation in human embryonic hepatic tissues. In summary, these studies suggest that ethanol may affect the biosynthesis of t-RA in human prenatal hepatic tissues directly and indirectly. Ethanol and its major oxidative metabolite, acetaldehyde, both inhibit the generation of t-RA. Concurrently, the CYP2E1-catalyzed oxidation of ethanol can initiate lipid peroxidation via generation of a variety of free radicals. The lipid peroxides thereby generated could then be further converted via CYP2E1-catalyzed reactions to alcohols and aldehydes, including 4-HNE, that act as potent inhibitors of t-RA synthesis.

Characterization of interintestinal and intraintestinal variations in human CYP3A-dependent metabolism

Cytochrome P450 3A (CYP3A) metabolizes a diverse array of clinically important drugs. For some of these (e.g., cyclosporine, verapamil, midazolam), CYP3A in the intestinal mucosa contributes to their extensive and variable first-pass extraction. To further characterize this phenomenon, we measured CYP3A content and catalytic activity toward the probe substrate midazolam in mucosa isolated from duodenal, jejunal and ileal sections of 20 human donor intestines. For comparison, the same measurements were performed for 20 human donor livers, eight of which were obtained from the same donors as eight of the intestines. Excellent correlations existed between homogenate and microsomal CYP3A content for the three intestinal regions. Median microsomal CYP3A content was greatest in the duodenum and lowest in the ileum (31 vs. 17 pmol/mg of protein). With respect to midazolam 1'-hydroxylation kinetics, the median Km for each intestinal region was similar to the median hepatic Km, approximately 4 microM. In contrast, the median Vmax decreased from liver to duodenum to jejunum to ileum (850 vs. 644 vs. 426 vs. 68 pmol/min/mg). Intrinsic clearance (Vmax/Km) followed a similar trend for the intestinal regions; median duodenal intrinsic clearance was comparable to hepatic intrinsic clearance (157 and 200 microl/min/mg, respectively). Vmax correlated with CYP3A content for all tissues except the ileum. Duodenal and jejunal Vmax and CYP3A content varied by >30-fold among donors. Microsomes prepared from every other 1-foot section of six intestines were also analyzed for CYP3A as well as for two coenzymes. In general, CYP3A activity, CYP3A content and CYP reductase activity rose slightly from duodenum to middle jejunum and then declined to distal jejunum and ileum. Cytochrome b5 content and cytochrome b5 reductase activity varied little throughout the intestinal tract. Regional intrinsic midazolam 1'-hydroxylation clearance was greatest for the jejunum, followed by the duodenum and ileum (144, 50 and 19 ml/min, respectively). Collectively, these results demonstrate that the upper small intestine serves as the major site for intestinal CYP3A-mediated first-pass metabolism and provides a rationale for interindividual differences in oral bioavailability for some CYP3A substrates.

High-titer bicistronic retroviral vectors employing foot-and-mouth disease virus internal ribosome entry site

Bicistronic retroviral vectors were constructed containing the foot-and-mouth disease virus (FMDV) internal ribosome entry site (IRES) followed by the coding region of beta-galactosidase (beta-gal) or therapeutic genes, with the selectable neomycin phosphotransferase gene under the control of the viral long terminal repeat (LTR) promoter. LNFX, a vector with a multiple cloning site 3' to foot-and-mouth disease virus IRES, was used to construct vectors encoding rat erythropoietin (EP), rat granulocyte colony-stimulating factor (G-CSF), human adenosine deaminase (ADA) and beta-gal. In transduced primary rat vascular smooth muscle cells the cytokines were expressed at high levels, similar to those obtained from vectors employing the viral LTR promoter. LNFZ, a vector encoding beta-gal, had a 10-fold increase in titer over that of LNPoZ, a comparable vector containing the poliovirus (Po) internal ribosome entry site. Primary canine vascular smooth muscle cells infected with LNFZ and LNPoZ expressed similar activities of beta-gal and neomycin phosphotransferase (NPT). Overall, these vectors had titers between 10(6) and 2 x 10(7) c.f.u./ml, indicating that foot-and-mouth disease virus IRES provides high-titer bicistronic vectors with high-level two gene expression.