A kinetics-based approach to amyloid PET semi-quantification

Abstract

Purpose To develop and validate a semi-quantification method (time-delayed ratio, TDr) applied to amyloid PET scans, based on tracer kinetics information. Methods The TDr method requires two static scans per subject: one early (~0-10 min after the injection) and one late (typically 50-70 min or 90-100 min after the injection, depending on the tracer). High perfusion regions are delineated on the early scan and applied onto the late scan. A SUVr-like ratio is calculated between the average intensities in the high perfusion regions and the late scan hotspot. TDr was applied to a naturalistic multicenter dataset of 143 subjects acquired with [ 18 F]florbetapir. TDr values are compared to visual evaluation, cortical-cerebellar SUVr, and to the geometrical semi-quantification method ELBA. All three methods are gauged versus the heterogeneity of the dataset.Results TDr shows excellent agreement with respect to the binary visual assessment (AUC = 0.99) and significantly correlates with both validated semi-quantification methods, reaching a Pearson correlation coefficient of 0.86 with respect to ELBA. Conclusions TDr is an alternative approach to previously validated ones (SUVr and ELBA). It requires minimal image processing; it is independent on predefined regions of interest and does not require MR registration. Besides, it takes advantage on the availability of early scans which are becoming common practice while imposing a negligible added patient discomfort.

A comparison of advanced semi-quantitative amyloid PET analysis methods

“…Each amy-PET was semi-quantitatively assessed by means of five independent approaches (hereinafter referred to as quantifiers ): SUVr [ 19 ], ELBA [ 20 ], TDr [ 22 ], WMR [ 23 ], and SI [ 23 ]. Details of each quantifier can be found in their respective papers.…”

“…TDr is defined in [ 22 ] and is the ratio of counts exploiting the information on tracer kinetics provided by dual time-point acquisition to adapt both the target and the reference ROIs of each individual.…”

“…Besides SUVr, the most widely used [ 19 ] method, various alternatives using different sources of information are available. Analysis can be based on standard late acquisition alone, as with methods like ELBA or Aβ L [ 20 , 21 ], or can include tracer kinetic information obtained by adding early acquisition, as with TDr [ 22 ]. Our group proposed a more sophisticated procedure, called the Slope Index (SI), which also takes into consideration atrophy and spillover by including MRI data [ 23 ].…”

Amyloid PET in the diagnostic workup of neurodegenerative disease

“…Although visual reading is clinically adequate in clearly positive or negative cases, it is in a non-negligible fraction of cases the presence of a positive or negative amy-PET cannot be easily captured using only visual evaluation [9]. Semiquantitative assessment can better identify borderline cases and support the nuclear medicine physician in the informed writing of the clinical report.…”

“…Thus, the adoption of validated and standardized quantification methods of amy-PET to accurately define the presence of brain amyloidosis in research and clinical settings has become essential. Different approaches have been proposed for semi-quantitative analysis of amy-PET imaging [9][10][11].…”