A mobile friendly slideshow of this post about xSPECT bone can be found here. For those with a professional interest see our paper in the European Journal of Hybrid Imaging and visit Siemens healthineers.
Nuclear Imaging: The old v new
I have noted elsewhere about the dramatic transformation between “the old” and “the new” nuclear medicine that has taken place over the last decade (see my post Nuclear Medicine = New Clear Medicine). Fusing together nuclear medicine and CT scans was given the description SPECT-CT. This is a mouthful -the SPECT meaning “single photon emission computerised tomography” and representing cross sectional nuclear medicine. No one outside the field understand the acronym. The CT represents the much better know computerised tomography or “CAT” scan. In essence SPECT-CT brought anatomic x-ray together with functional nuclear medicine.
The limitation of SPECT-CT remained the poor spatial resolution of the SPECT component of the fused imaging. This limitation seemed fundamental as a gamma wave emanating inside a patient cannot provide the spatial resolution of an x-ray being fired in a parallel beam from outside. Siemens however came up with an ingenious solution by using the detailed spatial information about the tissues from the CT scan to reinterpret the gamma wave (SPECT) data arriving from within the patient.
How xSPECT bone works
Essentially the gamma wave data matrix is combined with the CT scan data matrix to re-engineer that gamma information at a fundamental level. I suggest skipping the next paragraph…
In their publications Siemens notes “Using CT-based segmentation in the reconstruction, xSPECT Bone achieves a sharper definition of bony margins and lesion boundaries. The resulting reconstructed SPECT images (xSPECT Bone) appear to truly reflect the distribution of metabolically active bone within the skeletal system with sharper differentiation between cortical and spongy bone in the vertebrae, as well as in flat bones like the pelvis, scapula and skull. This also provides fine detail which helps differentiate between the cortex and marrow cavity in long bones and improved separation of bone from joint spaces—both for large joints such as the knee and shoulder and for small bones such as carpals and tarsal bones.”
The end result is a high resolution bone scan rather than the limited resolution of standard SPECT.
The dramatic difference in the SPECT data can be appreciated even by the amateur. Fig 2 shows the xSPECT data on a single slice of the human pelvis and Fig 1 the exact same slice using conventional SPECT bone reconstruction (images courtesy of Garran Medical Imaging).
Figs 1-2 below.
This advance has side stepped the physical limitation of gamma-ray imaging by using x-ray data to “re-engineer” the raw data obtained from the gamma camera and redistribute the uptake according to the know properties of each tissue voxel obtained direct from the CT (x-ray) data. The bone uptake resolution is taken to a new level thus bypassing the previous bottleneck.
The images in Fig.3 are courtesy of Jason Tse1, Farshid Salehzahi1, and Nick Ingold2 and were part of a quantitative resolution study that shows the superior resolution and contrast of xSPECT. These were performed on our equipment at Garran Medical Imaging.
What does xSPECT bone mean for the patient and referring doctor?
The cases below all show bone isotope uptake in some very small locations that were previously rarely identified on SPECT-CT (again images courtesy Garran Medical Imaging).
Our first 200 cases have shown us that xSPECT imaging makes a BIG difference, giving additional information in in 71% of scans and changing the diagnosis in 20%, when compared to the current best SPECT scans. For the whole study see our research in the European Journal of Hybrid Imaging.
All of these xSPECT-CT scans (Figs 3-5 above) show abnormalities that could not be localised with conventional SPECT-CT alone.
Dr Iain Duncan has been a pioneer in the application of this technology and was recently invited to share his experience with others at a World Molecular Imaging Summit in Lausanne, Switzerland, May 2019 (sponsored by Siemens Healthineers).
For more about xSPECT bone see Dr Duncan’s research.
See our video with a 1minute UPDATE on Molecular Imaging without compromise.