Investigation of (11)C-PiB equivocal PET findings

Semiquantitative Approach to Amyloid Positron Emission Tomography Interpretation in Clinical Practice

Objective  Amyloid positron emission tomography (PET) plays a vital role in the in vivo detection of β-amyloid accumulation in Alzheimer's disease. Increasingly, trainees and infrequent readers are relying on semiquantitative analyses to support clinical diagnostic efforts. Our objective was to determine if the visual assessment of amyloid PET may be facilitated by relying on semiquantitative analysis. Methods  We conducted a retrospective review of [ ¹⁸ F]-florbetaben PET/computed tomographies (CTs) from 2016 to 2018. Visual interpretation to determine Aβ+ status was conducted by two readers blinded to each other's interpretation. Scans were then post-processed utilizing the MIMneuro software, which generated regional-based semiquantitative Z-scores indicating cortical Aβ-burden. Results  Of 167 [ ¹⁸ F]-florbetaben PET/CTs, 92/167 (reader-1) and 101/167 (reader-2) were positive for amyloid deposition (agreement = 92.2%, κ = 0.84). Additional nine scans were identified as possible Aβ-positive based solely on semiquantitative analyses. Largest semiquantitative differences were identified in the left frontal lobe (Z = 7.74 in Aβ + ; 0.50 in Aβ - ). All unilateral regions showed large statistically significant differences in Aβ-burden ( P ≤ 2.08E-28). Semiquantitative scores were highly sensitive to Aβ+ status and accurate in their ability to identify amyloid positivity, defined as a positive scan by both readers (AUC ≥ 0.90 [0.79-1.00]). Spread analyses suggested that amyloid deposition was most severe in the left posterior cingulate gyrus. The largest differences between Aβ +/Aβ- were in the left frontal lobe. Analyses using region-specific cutoffs indicated that the presence of amyloid in the temporal and anterior cingulate cortex, while exhibiting relatively low Z-scores, was most common. Conclusion  Visual assessment and semiquantitative analysis provide highly congruent results, thereby enhancing reader confidence and improving scan interpretation. This is particularly relevant, given recent advances in amyloid-targeting disease-modifying therapeutics.

From clinical phenotype to proteinopathy: molecular neuroimaging in neurodegenerative dementias

Neurodegenerative dementias are characterized by the abnormal accumulation of misfolded proteins. However, its diagnostic criteria are still based on the clinical phenotype. The development of biomarkers allowed in vivo detection of pathophysiological processes. This article aims to make a non-systematic review of the use of molecular neuroimaging as a biomarker. Molecular neuroimaging is based on the use of radiotracers for image acquisition. The radiotracer most used in PET is 18F-fluorodeoxyglucose (FDG), with which it is possible to study the regional brain glucose metabolism. The pattern of regional hypometabolism provides neuroanatomical information on the neurodegenerative process, which, in turn, has a good specificity for each type of proteinopathy. FDG is very useful in the differential diagnosis of neurodegenerative dementias through the regional pattern of involvement, including dementia with Lewy bodies and the spectrum of frontotemporal dementia. More recently, radiotracers with specific ligands to some of the pathological proteins have been developed. Pittsburgh compound B (PIB) labeled with 11C and the ligands that use 18F (florbetapir, florbetaben and flutemetamol) are the most used radiotracers for the detection of insoluble β-amyloid peptide in Alzheimer's disease (AD). A first generation of ligands for tau protein has been developed, but it has some affinity for other non-tau protein aggregates. A second generation has the advantage of having a higher affinity for hyperphosphorylated tau protein, including in primary tauopathies.

Lung carcinoma-associated cognitive impairment in a patient with Alzheimer's disease pathology: A case report

A patient with Alzheimer's disease (AD) pathology when cognitive impairment is detected tends to be diagnosed with AD. However, before diagnosing, we make an effort to exclude other diseases, for example, carcinoma.

A 4-Year Follow-Up of Subjects with Visually Equivocal Amyloid Positron Emission Tomography Findings from the Alzheimer's Disease Neuroimaging Initiative Cohort

Background

To date, the clinical significance of visually equivocal amyloid positron emission tomography (PET) has not been well established.

Objective

We studied the clinical significance of equivocal amyloid PET images from the Alzheimer's Disease Neuroimaging Initiative (ADNI).

Methods

Subjects with F-18 florbetapir PET scans at baseline who were followed up for 4 years were selected. Clinical characteristics, imaging biomarkers, cognitive function, and rate of conversion to AD were compared in subjects with visually equivocal findings.

Results

Of 249 subjects who completed the follow-up, 153 (61.4%), 20 (8.0%), and 129 (30.5%) were F-18 florbetapir-negative, -equivocal, and -positive, respectively. The mean standardized uptake value ratios (SUVR) of F-18 florbetapir PET were 0.75 ± 0.04, 0.85 ± 0.10, and 1.00 ± 0.09 for each group (p <0.001 between groups), and 15.0%, 70.0%, and 98.7% of patients were quantitatively above the positive threshold. The change in the SUVR of F-18 florbetapir PET was higher in the equivocal (6.09 ± 3.61%, p <0.001) and positive (3.13 ± 4.38%, p <0.001) groups than the negative group (0.88 ± 4.28%). Among the subjects with normal or subjective memory impairment and mild cognitive impairment, 5.3% with negative amyloid PET and 37.5% with positive amyloid PET converted to AD over the 4-year period. None of the equivocal amyloid PET subjects converted to AD during this period.

Conclusion

Approximately 8% of subjects from the ADNI cohort showed visually equivocal amyloid PET scans with intermediate load and rapid accumulation of amyloid, but did not convert to AD during the 4-year follow-up.

Evaluation of a visual interpretation method for tau-PET with 18F-flortaucipir

INTRODUCTION

Positron emission tomography targeting tau (tau-PET) is a promising diagnostic tool for the identification of Alzheimer's disease (AD). Currently available data rely on quantitative measures, and a visual interpretation method, critical for clinical translation, is needed.

METHODS

We developed a visual interpretation method for 18F-flortaucipir tau-PET and tested it on 274 individuals (cognitively normal controls, patients with mild cognitive impairment [MCI], AD dementia, and non-AD diagnoses). Two readers interpreted 18F-flortaucipir PET using two complementary indices: a global visual score and a visual distribution pattern.

RESULTS

Global visual scores were reliable, correlated with global cortical 18F-flortaucipir standardized uptake value ratio (SUVR) and were associated with clinical diagnosis and amyloid status. The AD-like 18F-flortaucipir pattern had good sensitivity and specificity to identify amyloid-positive patients with AD dementia or MCI.

DISCUSSION

This 18F-flortaucipir visual rating scheme is associated with SUVR quantification, clinical diagnosis, and amyloid status, and constitutes a promising approach to tau measurement in clinical settings.

Artificial Intelligence for Optimization and Interpretation of PET/CT and PET/MR Images

Artificial intelligence (AI) has recently attracted much attention for its potential use in healthcare applications. The use of AI to improve and extract more information out of medical images, given their parallels with natural images and the immense progress in the area of computer vision, has been at the forefront of these advances. This is due to a convergence of factors, including the increasing numbers of scans performed, the availability of open source AI tools, and decreases in the costs of hardware required to implement these technologies. In this article, we review the progress in the use of AI toward optimizing PET/CT and PET/MRI studies. These two methods, which combine molecular information with structural and (in the case of MRI) functional imaging, are extremely valuable for a wide range of clinical indications. They are also tremendously data-rich modalities and as such are highly amenable to data-driven technologies such as AI. The first half of the article will focus on methods to improve PET reconstruction and image quality, which has multiple benefits including faster image acquisition, image reconstruction, and lower or even "zero" radiation dose imaging. It will also address the value of AI-driven methods to perform MR-based attenuation correction. The second half will address how some of these advances can be used to perform to optimize diagnosis from the acquired images, with examples given for whole-body oncology, cardiology, and neurology indications. Overall, it is likely that the use of AI will markedly improve both the quality and safety of PET/CT and PET/MRI as well as enhance our ability to interpret the scans and follow lesions over time. This will hopefully lead to expanded clinical use cases for these valuable technologies leading to better patient care.

Progressive amnestic cognitive impairment in a middle-aged patient with developmental language disorder: a case report

BACKGROUND

Developmental disorder and dementia in older adults have been considered unrelated clinical entities because their timing of diagnosis differs greatly; however, recent studies have suggested an association between them. This case describes a middle-aged patient with language disorder exhibiting progressive amnestic cognitive impairment.

CASE PRESENTATION

A 44-year-old Japanese man with long-term language dysfunction presented for his first-ever medical evaluation at age 36 years. Although his conversational ability had been impaired since childhood, he was able to graduate from secondary school and gain unskilled employment. At age 36 years, however, his workplace environment became more stressful, which led to behavioral problems that necessitated medical consultation. He consulted two psychiatrists in vain. At age 44 years, the third attending psychiatrist examined him in detail. The major component of his language disorder was amnestic cognitive impairment in the language domain as shown by logical memory subtests of the Wechsler Memory Scale-Revised. Magnetic resonance imaging showed normal findings for his age and no small vessel disease. Global cerebral hypoperfusion versus cerebellar blood flow was shown on (¹²³I) iodoamphetamine single-photon emission computed tomography, and amyloid-β deposition was negative on positron emission tomography with ¹¹C-Pittsburgh compound B. Pathologic tau accumulation was negative on ¹⁸F-THK5351 positron emission tomography imaging. Laboratory tests show no infections, no vitamin deficiencies, and no other diseases that may cause dementia. Clinical features, results of neurocognitive tests and neuroimaging studies showed no well-known neurodegenerative diseases. Collectively, he was diagnosed with language disorder based on the Diagnostic and Statistical Manual of Mental Disorders, Fifth Edition criteria. Over a 2-year follow-up period, amnestic cognitive impairment in visual and language domains progressed in parallel with global cerebral hypoperfusion.

CONCLUSION

This case suggests a possible link between language disorder as defined by Diagnostic and Statistical Manual of Mental Disorders, Fifth Edition criteria and progressive amnestic cognitive impairment in middle age, which may ultimately lead to dementia, derived from a neurodegenerative disease.

What to make of equivocal amyloid imaging results

INTRODUCTION

Six patients with equivocal amyloid-PET results are discussed.

METHODS

Patients underwent clinical/neuropsychological assessment, MRI, and amyloid-PET. Equivocal amyloid-PET was defined as cortical ligand binding with SUVR < 1.40. Follow-up for up to 5 years is presented.

RESULTS

6 patients (4 males, 2 females, mean age 71.8 +/- 2.5 years) with equivocal amyloid-PET were included from 136 patients who underwent amyloid-PET (4.4% of cases). Patients had variable language, behavioral, and cognitive deficits. Progression varied from no deterioration to residential care within 3 years.

DISCUSSION

Equivocal amyloid-PET should be interpreted cautiously. Improved biomarkers of AD and other neurodegenerative diseases are needed.

The clinical feasibility of deep learning-based classification of amyloid PET images in visually equivocal cases

PURPOSE

Although most deep learning (DL) studies have reported excellent classification accuracy, these studies usually target typical Alzheimer's disease (AD) and normal cognition (NC) for which conventional visual assessment performs well. A clinically relevant issue is the selection of high-risk subjects who need active surveillance among equivocal cases. We validated the clinical feasibility of DL compared with visual rating or quantitative measurement for assessing the diagnosis and prognosis of subjects with equivocal amyloid scans.

METHODS

¹⁸F-florbetaben scans of 430 cases (85 NC, 233 mild cognitive impairment, and 112 AD) were assessed through visual rating-based, quantification-based, and DL-based methods. DL was trained using 280 two-dimensional PET images (80%) and tested by randomly assigning the remaining (70 cases, 20%) cases and a clinical validation set of 54 equivocal cases. In the equivocal cases, we assessed the agreement among the visual rating, quantification, and DL and compared the clinical outcome according to each modality-based amyloid status.

RESULTS

The visual reading was positive in 175 cases, equivocal in 54 cases, and negative in 201 cases. The composite SUVR cutoff value was 1.32 (AUC 0.99). The subject-level performance of DL using the test set was 100%. Among the 54 equivocal cases, 37 cases were classified as positive (Eq(deep+)) by DL, 40 cases were classified by a second-round visual assessment, and 40 cases were classified by quantification. The DL- and quantification-based classifications showed good agreement (83%, κ = 0.59). The composite SUVRs differed between Eq(deep+) (1.47 [0.13]) and Eq(deep-) (1.29 [0.10]; P < 0.001). DL, but not the visual rating, showed a significant difference in the Mini-Mental Status Examination score change during the follow-up between Eq(deep+) (- 4.21 [0.57]) and Eq(deep-) (- 1.74 [0.76]; P = 0.023) (mean duration, 1.76 years).

CONCLUSIONS

In visually equivocal scans, DL was more related to quantification than to visual assessment, and the negative cases selected by DL showed no decline in cognitive outcome. DL is useful for clinical diagnosis and prognosis assessment in subjects with visually equivocal amyloid scans.

Evaluation of PiB visual interpretation with CSF Aβ and longitudinal SUVR in J-ADNI study

Objective

The objectives of the present study were to investigate (1) whether trinary visual interpretation of amyloid positron emission tomography (PET) imaging (negative/equivocal/positive) reflects quantitative amyloid measurements and the time course of ¹¹C-Pittsburgh compound B (PiB) amyloid accumulation, and (2) whether visually equivocal scans represent an early stage of the Alzheimer’s disease (AD) continuum in terms of an intermediate state of quantitative amyloid measurements and the changes in amyloid accumulation over time.

Methods

From the National Bioscience Database Center Human Database of the Japanese Alzheimer’s Disease Neuroimaging Initiative, we selected 133 individuals for this study including 33 with Alzheimer’s disease dementia (ADD), 52 with late mild cognitive impairment (LMCI), and 48 cognitively normal (CN) subjects who underwent clinical assessment, PiB PET, and structural magnetic resonance imaging (MRI) with 2 or 3-years of follow-up. Sixty-eight of the 133 individuals underwent cerebrospinal fluid amyloid-β_1-42 (CSF-Ab₄₂) analysis at baseline. The standard uptake value ratio (SUVR) of PiB PET was calculated with a method using MRI at each visit. The cross-sectional values, longitudinal changes in SUVR, and baseline CSF-Ab₄₂ were compared among groups, which were categorized based on trinary visual reads of amyloid PET (negative/equivocal/positive).

Results

From the trinary visual interpretation of the PiB PET images, 55 subjects were negative, 8 were equivocal, and 70 were positive. Negative interpretation was most frequent in the CN group (70.8/10.4/18.8%: negative/equivocal/positive), and positive was most frequent in the LMCI group (34.6/1.9/63.5%) and in the ADD group (9.1/6.1/84.8%). The baseline SUVRs were 1.08 ± 0.06 in the negative group, 1.23 ± 0.15 in the equivocal group, and 1.86 ± 0.31 in the positive group (F = 174.9, p < 0.001). The baseline CSF-Ab₄₂ level was 463 ± 112 pg/mL in the negative group, 383 ± 125 pg/mL in the equivocal group, and 264 ± 69 pg/mL in the positive group (F = 37, p < 0.001). Over the 3-year follow-up, annual changes in SUVR were − 0.00 ± 0.02 in the negative group, 0.02 ± 0.02 in the equivocal group, and 0.04 ± 0.07 in the positive group (F = 8.4, p < 0.001).

Conclusions

Trinary visual interpretation (negative/equivocal/positive) of amyloid PET imaging reflects quantitative amyloid measurements evaluated with PET and the CSF amyloid test as well as the amyloid accumulation over time evaluated with PET over 3 years. Subjects in the early stage of the AD continuum could be identified with an equivocal scan, because they showed intermediate quantitative amyloid PET, CSF measurements, and the amyloid accumulation over time.

Electronic supplementary material

The online version of this article (10.1007/s12149-019-01420-2) contains supplementary material, which is available to authorized users.

Clinical significance of visually equivocal amyloid PET findings from the Alzheimer's Disease Neuroimaging Initiative cohort

To evaluate the clinical and imaging characteristics of patients with visually equivocal amyloid PET images, patients from the Alzheimer's Disease Neuroimaging Initiative cohort who had fluorine-18-florbetapir PET scans both at baseline and 24 months were selected. Five nuclear medicine physicians visually assessed the PET images and classified them as either positive or negative. Images not reaching a majority agreement were classified as equivocal. Among a total of 379 patients, the number of patients in each fluorine-18-florbetapir PET negative/equivocal/positive categories was 218 (57.5%), 32 (8.4%), and 129 (34.0%). Eight to 9% of patients with normal cognition (N=12/141), mild cognitive impairment (N=20/214), and no Alzheimer's disease (N=0/24) showed equivocal PET finding for each. In negative/equivocal/positive groups, positive cerebrospinal fluid Aβ1-42 was observed in 25.7, 81.5, and 98.3%, respectively. Baseline standardized uptake value ratios of fluorine-18-florbetapir PET were 0.75±0.05, 0.86±0.09, and 1.01±0.09, respectively [F(2, 376)=603.547; P<0.001]. After 24 months of follow-up, the standardized uptake value ratios increased by 0.81±2.62, 2.81±2.90, and 2.17±3.66%, respectively [F(2, 376)=7.905, P<0.05 vs. the negative group]. Among mild cognitive impairment patients, the equivocal group showed a more rapid decline in glucose metabolism than the negative group [5.52±5.36 vs. 0.67±4.45; F(2, 122)=9.028, P<0.01]. 8.4% of the patients in this study showed a visually equivocal result of amyloid PET. These patients showed a moderate amount of amyloid accumulation and a rapid rate of accumulation.

Topography of 11C-Pittsburgh compound B uptake in Alzheimer's disease: a voxel-based investigation of cortical and white matter regions

Objective:

To compare results of positron emission tomography (PET) with carbon-11-labeled Pittsburgh compound B (¹¹C-PIB) obtained with cerebellar or global brain uptake for voxel intensity normalization, describe the cortical sites with highest tracer uptake in subjects with mild Alzheimer’s disease (AD), and explore possible group differences in ¹¹C-PIB binding to white matter.

Methods:

¹¹C-PIB PET scans were acquired from subjects with AD (n=17) and healthy elderly controls (n=19). Voxel-based analysis was performed with statistical parametric mapping (SPM).

Results:

Cerebellar normalization showed higher ¹¹C-PIB uptake in the AD group relative to controls throughout the cerebral cortex, involving the lateral temporal, orbitofrontal, and superior parietal cortices. With global uptake normalization, greatest cortical binding was detected in the orbitofrontal cortex; decreased ¹¹C-PIB uptake in white matter was found in the posterior hippocampal region, corpus callosum, pons, and internal capsule.

Conclusion:

The present case-control voxelwise ¹¹C-PIB PET comparison highlighted the regional distribution of amyloid deposition in the cerebral cortex of mildly demented AD patients. Tracer uptake was highest in the orbitofrontal cortex. Decreased ¹¹C-PIB uptake in white-matter regions in this patient population may be a marker of white-matter damage in AD.

The correlation between striatal and cortical binding ratio of 11C-PiB-PET in amyloid-uptake-positive patients

PURPOSE

In subjects with amyloid deposition, striatal accumulation of ¹¹C-Pittsburgh compound B (PiB) demonstrated by positron emission tomography (PET) is related to the stage of Alzheimer's disease (AD). In this study, we investigated the correlation between striatal and cortical non-displaceable binding potential (BP_ND).

METHODS

Seventy-three subjects who complained of cognitive disturbance underwent dynamic PiB-PET studies and showed positive PiB accumulation were retrospectively selected. These subjects included 34 AD, 26 mild cognitive impairment, 2 frontotemporal lobar degeneration, 2 Parkinson's disease, 5 dementia with Lewy bodies, and 4 undefined diagnosis patients. Individual BP_ND images were produced from the dynamic data of the PiB-PET study, and voxel-based analyses were performed to estimate the correlations between striatal and other regional cortical BP_ND measures.

RESULTS

There were highly significant correlations between striatal and prefrontal BP_ND, with the highest correlation being demonstrated in left Brodmann area 11. We found that almost all of the high cortical BP_ND values correlated with striatal BP_ND values, with the exception of the occipital cortex with low correlation.

CONCLUSION

Our study demonstrated positive correlations in amyloid deposits between the striatum and other cortical areas with functional and anatomical links. The amyloid distribution in the brain is not random, but spreads following the functional and anatomical connections.

Tau accumulation in two patients with frontotemporal lobe degeneration showing different types of aphasia using 18F-THK-5351 positron emission tomography: a case report

ABSTRACTTau deposits in Alzheimer's disease and corticobasal syndrome have been reported using 18F-THK-5351 positron emission tomography (PET). To our knowledge, our study is the first to demonstrate tau deposits in patients with frontotemporal lobe degeneration (FTLD), using 18F-THK-5351 PET. This case report presents two patients, both of whom showed positive Tau deposition using 18F-THK-5351 PET. One patient was diagnosed with semantic variant primary progressive aphasia (PPA) and the other diagnosed with logopenic variant PPA. Our results suggest an association in the pathology of Alzheimer's disease, corticobasal syndrome, and FTLD, and could plan more effective clinical care in advance.

Impact of spillover from white matter by partial volume effect on quantification of amyloid deposition with [11C]PiB PET

High non-specific uptake of [¹¹C]Pittsburgh compound B ([¹¹C]PiB) in white matter and signal spillover from white matter, due to partial volume effects, confound radioactivity measured in positron emission tomography (PET) with [¹¹C]PiB. We aimed to reveal the partial volume effect in absolute values of kinetic parameters for [¹¹C]PiB, in terms of spillover from white matter. Dynamic data acquired in [¹¹C]PiB PET scans with five healthy volunteers and eight patients with Alzheimer's disease were corrected with region-based and voxel-based partial volume corrections. Binding potential (BP_ND) was estimated using the two-tissue compartment model analysis with a plasma input function. Partial volume corrections significantly decreased cortical BP_ND values. The degree of decrease in healthy volunteers (-52.7±5.8%) was larger than that in Alzheimer's disease patients (-11.9±4.2%). The simulation demonstrated that white matter spillover signals due to the partial volume effect resulted in an overestimation of cortical BP_ND, with a greater degree of overestimation for lower BP_ND values. Thus, an overestimation due to partial volume effects is more severe in healthy volunteers than in Alzheimer's disease patients. Partial volume corrections may be useful for accurately quantifying Aβ deposition in cortical regions.