title: Evaluation of a CdTe semiconductor based compact γ camera for sentinel lymph node imaging.
abstract: OBJECTIVE
  The authors assembled a prototype compact gamma-ray imaging probe (MediPROBE) for sentinel lymph node (SLN) localization. This probe is based on a semiconductor pixel detector. Its basic performance was assessed in the laboratory and clinically in comparison with a conventional gamma camera.
  
  
  METHODS
  The room-temperature CdTe pixel detector (1 mm thick) has 256 x 256 square pixels arranged with a 55 microm pitch (sensitive area 14.08 x 14.08 mm2), coupled pixel-by-pixel via bump-bonding to the Medipix2 photon-counting readout CMOS integrated circuit. The imaging probe is equipped with a set of three interchangeable knife-edge pinhole collimators (0.94, 1.2, or 2.1 mm effective diameter at 140 keV) and its focal distance can be regulated in order to set a given field of view (FOV). A typical FOV of 70 mm at 50 mm skin-to-collimator distance corresponds to a minification factor 1:5. The detector is operated at a single low-energy threshold of about 20 keV.
  
  
  RESULTS
  For 99 mTc, at 50 mm distance, a background-subtracted sensitivity of 6.5 x 10(-3) cps/kBq and a system spatial resolution of 5.5 mm FWHM were obtained for the 0.94 mm pinhole; corresponding values for the 2.1 mm pinhole were 3.3 x 10(-2) cps/kBq and 12.6 mm. The dark count rate was 0.71 cps. Clinical images in three patients with melanoma indicate detection of the SLNs with acquisition times between 60 and 410 s with an injected activity of 26 MBq 99 mTc and prior localization with standard gamma camera lymphoscintigraphy.
  
  
  CONCLUSIONS
  The laboratory performance of this imaging probe is limited by the pinhole collimator performance and the necessity of working in minification due to the limited detector size. However, in clinical operative conditions, the CdTe imaging probe was effective in detecting SLNs with adequate resolution and an acceptable sensitivity. Sensitivity is expected to improve with the future availability of a larger CdTe detector permitting operation at shorter distances from the patient skin.
authors.affiliation: Dipartimento di Scienze Fisiche, Università di Napoli Federico II, I-80126 Napoli, Italy. russo@na.infn.it
authors.forename: Paolo
authors.initials: P
authors.lastname: Russo
authors.forename: Assunta S
authors.initials: AS
authors.lastname: Curion
authors.forename: Giovanni
authors.initials: G
authors.lastname: Mettivier
authors.forename: Michela
authors.initials: M
authors.lastname: Esposito
authors.forename: Michela
authors.initials: M
authors.lastname: Aurilio
authors.forename: Corradina
authors.initials: C
authors.lastname: Caracò
authors.forename: Luigi
authors.initials: L
authors.lastname: Aloj
authors.forename: Secondo
authors.initials: S
authors.lastname: Lastoria
mesh_terms: D019187:Cadmium Compounds; D016000:Cluster Analysis; D015902:Gamma Cameras; D006801:Humans; D008198:Lymph Nodes / Q000000981:diagnostic imaging*; D008545:Melanoma / Q000000981:diagnostic imaging; D015609:Organotechnetium Compounds; D011877:Radionuclide Imaging / Q000295:instrumentation*; D012666:Semiconductors; D012984:Software; D013691:Tellurium
chemical_list: D019187:Cadmium Compounds; D015609:Organotechnetium Compounds; D013691:Tellurium; C028337:cadmium telluride