| dc.description.abstract | The bone scan is a common nuclear medicine imaging procedure that is mainly used for
evaluating several oncological patient groups. A radioactive tracer, 99mTc -labelled
diphosphonate, is injected intravenously and accumulates in the skeleton. The distribution of
the tracer in the body is measured with a gamma camera 3 hours post-injection. Conventional
gamma cameras used in nuclear medicine are based on scintillation detectors made of
thallium-doped sodium iodine (NaI(Tl)). During recent years, progress has been made
regarding the production of direct conversion room temperature semiconductor-detectors. One
such detector is made of cadmium zinc telluride (CZT), and in comparison to NaI(Tl), CZT
has better energy resolution. In the spring of 2020, a NM/CT 870 CZT gamma camera
manufactured by GE Healthcare was installed at Sahlgrenska university hospital. The primary
aim of this study was to evaluate planar whole-body bone scans on a NM/CT 870 CZT
gamma camera by comparing the image quality with a conventional gamma camera.
Additional aims were to, for the NM/CT 870 CZT gamma camera, evaluate the effect that
reduced scan time/activity level and the use of the post-processing Clarity 2D has on the
image quality and to determine the effect that different Clarity 2D blending has on the spatial
resolution.
Two different patient groups were used for the retrospective visual grading study. The first
group consisted of 16 patients with advanced disease who had been scanned on both the
NM/CT 870 CZT and a conventional gamma camera at separate occasions. The second group
consisted of 32 patients who underwent their first bone scan, where 16 patients were scanned
on the NM/CT 870 CZT, while the other 16 were scanned on a conventional gamma camera.
For all examinations, the administered activity and scan time were approximately the same.
For the examinations performed on the NM/CT 870 CZT, the original images were used to
simulate 3 different scan times/activity levels (25 %, 50 % and 75 % of the original 100 %).
Additionally, 5 different Clarity 2D blendings were used for each level. The evaluation was
accomplished by performing a visual grading characteristics (VGC) analysis in a beta-version
of the software ViewDEX 3.0, with two physicians participating as observers. Seven image
criteria were rated with a five-step ordinal scale, where the observers stated their confidence
on the fulfilment of each criterion. The software VGC Analyzer 1.0.2 was used to perform
statistical analysis of the observer ratings. The effect of Clarity 2D on the spatial resolution
was evaluated using a Triple Line Insert-phantom, model ECT/TRI/I. The images were also
evaluated quantitatively, the bone-to-soft tissue relationship was calculated by dividing the
average counts in the sinister sacroiliac joint with the standard deviation of counts in adjacent
soft tissue
The results showed that the original CZT images with no post-processing were graded equal
to or significantly higher than the images from the conventional gamma cameras for all image
quality criteria in both patient groups. For the CZT images with a simulated scan time/activity
level of 75 % of the original settings, no significant differences were found. The CZT images
with a simulated scan time/activity level of 50 % of the original settings were graded equal to
or significantly lower than the images from the conventional gamma cameras. The CZT
images with a simulated scan time/activity level of 25 % were graded significantly lower for
IV
most of the criteria. This indicated that the scan time/activity level for whole-body bone scans
on the NM/CT 870 CZT could be lowered to 75 % of the original setting without decreasing
the image quality compared to a conventional gamma camera. The results also showed that
the positive effect of Clarity 2D post-processing was more prominent in the simulated images
with reduced scan time/activity level. The quantitative measurements showed that the spatial
resolution as well as the bone-to-soft tissue relationship improved with increasing Clarity 2D
blendings. | sv |
