34 2011


IMAGING & ONCOLOGY


uptake can be more accurately localised when using SPECT/CT. Hybrid imaging has value when a SPECT acquisition fails to provide adequate anatomical detail. Lymphoscintigraphy is synonymous with this type of dilemma since the radionuclide uptake is highly specific. Precise registration of CT and SPECT data can overcome this where foci of uptake from SPECT data are superimposed upon the anatomical detail provided by CT. Acquiring CT data at a ‘diagnostic quality’ still permits a fused image; but the CT data are diagnostic in their own right and could be used to determine lesion/node position in isolation of SPECT data.


IMAGING THE SENTINEL NODE Preoperative localisation of the sentinel node(s) involves the injection of a radiopharmaceutical, followed by imaging. Imaging can be 2D planar ± SPECT or ± SPECT/CT with the intention of determining: • The number of lymph nodes • The sentinel node(s) • The location of the sentinel nodes(s)


Planar, SPECT and SPECT/CT imaging Despite the recent development of SPECT/CT, many papers have described the usefulness


of hybrid imaging for sentinel node detection. Warncke et al found that SPECT/CT better equipped surgeons to plan pre-surgical sentinel node identification, resulting in reduced operation times15


. Accurate determination of node positions by SPECT/CT


lymphoscintigraphy is highly valuable to the surgeon because it can facilitate a minimally invasive biopsy, thus reducing morbidity; it is also highly valuable for defining the involvement of supraclavicular lymph nodes, since this sub-group is associated with a poorer prognosis and may prompt an alternative treatment strategy16


. Non-identification


of the sentinel node, due to obesity and scattered radiation from the injection site, is a problem associated with planar imaging that SPECT/CT is able to resolve14,17


. Additional hot


nodes have been found in 13 per cent of patients compared to planar imaging, where the quality of planar imaging was reduced due to scattered radiation or the nodes had been on a less common drainage pathway18


cancer; Even-Sapir et al report improved detection rates in cases of trunk melanoma17


. The success of SPECT/CT is not limited to breast .


Sentinel node technique – nuclear medicine Many different combinations of injection and imaging technique exist for sentinel node


identification and, despite a lack of consensus on the optimal method, there appears to be a robustness of these techniques, yielding a high success rate (>96%) for breast cancer19


justification and explanation20 Tcm


. Somasundaram et al outline a well considered technique, providing good .


Radiopharmaceutical administration 99


-colloid is injected intradermally over the tumour or at the peri-areolar margin.


The precise site is dependent on the nature of the primary cancer and which path of lymphatic drainage is the focus (internal mammary, extra-axillary or axillary). The


identifiCation and evaluation of the sentinel node is


highly valuable


Figure 3. Static Planar image of axillary and internal mammary sentinel nodes. Planar scan of axillary (left) and internal mammary (right) sentinel nodes. Reprinted with permission from Aarsvold and Alazraki. Semin Nucl Med. 2005;35:116-128.19


Acquisition parameters Static planar imaging


High-resolution, low energy collimator 256 x 256 matrix 140keV energy peak, suitable window Acquired for set counts or set time


SPECT imaging


Low-energy, all purpose collimator 64 x 64 or 128 x 128 matrix 140keV energy peak, suitable window 360° rotation Step and shoot (20-30 seconds per frame)


Table 1. Example of static planar imaging and SPECT acquisition parameters.


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