Noninvasive Characterization of Myocardial Molecular Interventions by Integrated Positron Emission Tomography and Computed Tomography
Bettina Wagner, DVM*,
Martina Anton, PhD ,
Stephan G. Nekolla, PhD*,
Sybille Reder, MT*,
Julia Henke, DVM,
Stefan Seidl, MD ,
Renate Hegenloh, MT ,
Masao Miyagawa, MD*,
Roland Haubner, PhD*,
Markus Schwaiger, MD* and
Frank M. Bengel, MD*,||,*
* Nuklearmedizinische Klinik und Poliklinik
Institut für Experimentelle Onkologie und Therapieforschung
Institut für Allgemeine Pathologie und Pathologische Anatomie
Abteilung für Gefäßchirurgie, Technische Universität München, Germany
|| Division of Nuclear Medicine, Johns Hopkins University, Baltimore, Maryland
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Figure 1 Assessment of morphology and contractile function. (A) Contrast-enhanced multislice computed tomographic (CT) images obtained during positron emission tomography–CT in an animal (animal 5; Table 1) after adenoviral gene transfer (top) and a control animal (animal 10; Table 1) after saline injection (bottom). Surface-rendered images (left, anterior view) allow for accurate identification of clip-marked injection sites in basal anterior and distal anterolateral wall (arrows). Ventricular function is determined from end-diastolic (middle right) and end-systolic short-axis images (right). (B and C) Mean ± SD of regional end-diastolic wall thickness and thickening.
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Figure 2 Uptake of tracers of myocardial reporter gene expression and perfusion in regions of adenoviral gene transfer (AdTk-VEGF [n = 8]; AdVEGF [n = 4]; Adsr39tk [n = 4]; remote [n = 8]). (A) Regional uptake of the reporter probe [18F]fluoro-hydroxymethylbutyl-guanine (FHBG). *p < 0.01 vs. AdVEGF and remote. (B) Regional uptake of the perfusion tracer [13N]ammonia at rest. *p < 0.01 vs. Adsr39tk and remote. (C) [13N]ammonia uptake during adenosine vasodilation. *p < 0.01 vs. Adsr39tk and remote). Bars indicate mean ± SD.
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Figure 3 Positron emission tomography (PET)–computed tomographic (CT) imaging of morphology and biology. Representative short-axis tomographic images are shown. (A) Study animal (animal 1; Table 1) after regional injection of adenovirus carrying HSV1-sr39tk reporter gene together with VEGF121 gene (AdTk-VEGF, top row), or HSV1-sr39tk reporter gene only (Adsr39tk, bottom row). (B) Another study animal (animal 3; Table 1) after regional injection of AdTk-VEGF
(top row). This time, virus expressing VEGF121 only was used as internal control (AdVEGF, bottom row). (C) Control animal (animal 9; Table 1) after regional injection of saline at both sites. Columns from left to right: on the left, a schematic display of individual location and orientation of short-axis slices, along with injection sites (yellow) is shown; next, contrast-enhanced multislice CT depicts location of titanium clip markings (yellow arrows), along with circumferential wall thickness; next, PET-CT fusion of morphologic CT with PET images of the reporter probe [18F]fluoro-hydroxymethylbutyl-guanine (FHBG) show significant accumulation of FHBG, colocalizing with clip markings in areas expressing the HSV1-sr39tk reporter gene (animal A, both rows; animal B, top row); on the right, PET perfusion images at rest and during adenosine-induced vasodilation show significantly elevated [13N]ammonia uptake at sites where VEGF121 is overexpressed (animal A, top row; animal B, both rows), whereas it is regionally homogeneous after Adsr39tk injection (animal A, bottom row) or saline injection (animal C).
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Figure 4 Ex vivo immunohistochemical staining of transgene products. Shown are microscopic images of a representative sample from a myocardial area injected with adenovirus carrying HSV1-sr39tk reporter gene together with the VEGF121 gene (AdTk-VEGF). Immunostaining for HSV1-tk (A and C) and VEGF (B and D) was performed in adjacent slices. Dark brown color indicates presence of the respective gene product. Low magnification (A and B) shows corresponding expression of both transgene products in the same tissue region. High magnification (C and D) identifies HSV1-tk reporter gene product in cytosol and nuclei, whereas VEGF is found in cytosol only, partly in a vesicle-like pattern. Subtle differences in strength and cellular localization of the immunostaining signal are explained by gene product characteristics (HSV1-TK is an intracellular enzyme, VEGF is a secretable substance).
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Figure 5 Ex vivo immunohistochemical staining of microvessels. Pink color indicates presence of smooth muscle actin (small vessels indicated by arrows). Shown are microscopic images of samples from a myocardial area injected with adenovirus carrying HSV1-sr39tk only (Adsr39tk) (A), and of another area of the same animal injected with adenovirus carrying HSV1-sr39tk reporter gene together with the VEGF121 gene (AdTk-VEGF) (B). Higher microvascular density is present in the VEGF-exposed area.
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Figure 6 Positron emission tomography (PET)–computed tomographic (CT) imaging of integrin expression. Shown are representative short-axis slices through injection sites receiving adenovirus carrying the HSV1-sr39tk reporter gene together with the VEGF121 gene (AdTk-VEGF) in 2 different animals which underwent a repeat PET-CT session at 3 (top, animal 5; Table 1) or 9 (bottom, animal 7; Table 1) days after adenovirus injection. CT images (multislice computed tomography [MSCT], left) depict location of titanium clip markings of injection sites (yellow arrows). Middle left shows fusion of MSCT with PET images of the perfusion tracer [13N]ammonia at rest. PET perfusion images (middle right) show significant accumulation of [13N]ammonia at the site of AdTk-VEGF injection. PET images of [18F]-galacto-RGD (right) show no accumulation at vector injection sites.
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