Intraoperative 3-D mapping of parathyroid adenoma using freehand SPECT
© Rahbar et al.; licensee Springer. 2012
Received: 20 May 2012
Accepted: 18 September 2012
Published: 27 September 2012
Freehand single photon emission computed tomography (fSPECT) is a three-dimensional (3-D) tomographic imaging modality based on data acquisition with a handheld detector that is moved freely, in contrast to conventional, gantry-mounted gamma camera systems. In this pilot study, we evaluated the feasibility of fSPECT for intraoperative 3-D mapping in patients with parathyroid adenomas.
Three patients (range 30 to 45 years) diagnosed with hyperparathyroidism (one primary and two tertiary) underwent parathyroid scintigraphy with technetium-99m sestamibi (99mTc-MIBI) to localize parathyroid adenomas. Two patients were referred with persistent hyperparathyroidism after conventional parathyroidectomy. In all three patients, a planar scintigraphy of the neck was performed 10 min after injection (p.i.) followed by SPECT/CT (Symbia T2, Siemens Healthcare) and a correlative ultrasound 2 h p.i. 99mTc-MIBI scan was performed the day before surgery in two patients and at the same day in one patient. fSPECT images were acquired intraoperatively using declipse SPECT (SurgicEyeTM).
A total of five parathyroid adenomas were successfully located with SPECT/CT. fSPECT allowed intraoperative detection of all adenomas, and successful parathyroidectomy was accomplished. Parathyroid hormone level decreased intraoperatively in all three patients, on average, by 79% (range 72% to 91%).
In this preliminary study, we could demonstrate that intraoperative localization of parathyroid adenomas is feasible using the freehand SPECT technology, thus allowing an image-guided parathyroidectomy.
A total of three consecutive patients (age range 30 to 45 years) undergoing conventional 99mTc-MIBI whole-body scan to localize parathyroid adenomas before surgical procedure were additionally scanned intraoperatively using fSPECT. One patient suffered from primary hyperparathyroidism and two patients suffered from tertiary hyperparathyroidism. Preoperative SPECT/CT was performed routinely in all patients and served as reference imaging modality.
In all patients, a mean of 746 ± 12 MBq 99mTc-MIBI was injected intravenously according to the German guideline for parathyroid scintigraphy. The injection of the radiopharmaceutical and the fSPECT were performed in the clinical setting. The data were analyzed retrospectively. Patients attending the University Hospital signed an informed consent for such anonymized data analysis. In one patient (#3), we used a 1-day protocol. To achieve a better lesion-to-background ratio, a 2-day protocol was performed in the other two patients. No re-injection before surgery was performed in all cases. Time to surgery was about 4 h in the 1-day protocol and about 24 h in the 2-day protocol.
Parathyroid hormone (PTH) levels were measured preoperatively before draping, followed by further samples at the time of extirpation and 10 min thereafter. fSPECT images were generated under sterile conditions shortly before the skin incision and when extirpating each parathyroid adenoma in order to control parathyroidectomy.
The SPECT protocol consisted of 32 projections (180° using two opposing heads) of 10 s, each using a Symbia T2 hybrid scanner and low-energy high-resolution collimators (Siemens Healthcare, Erlangen, Germany). Low-dose CT was performed using a voltage of 130 kV with a tube current of 2.5 mA (20 mAs). SPECT/CT images were acquired with a reference marker to allow for navigation in the operating room.
The fSPECT protocol consisted of a 2- to 3-min scan (1,200 to 1,800 measurements, i.e., 20 measurements/second), covering one side of the neck and the corresponding periclavicular area using a declipse SPECT (SurgicEye, Munich, Germany) connected to a Crystal Probe (Crystal Photonics, Berlin, Germany) with a 40° collimator. The large number of measurements was achieved by continuously moving the probe. The device itself then decided which intervals are to be summarized as a complete projection. The scan was divided in a 1- to 2-min scan with the gamma probe pointing at a dorsal direction and a 1- to 2-min scan with the gamma probe pointing at a medial direction. Reconstruction was done using a modified ML-EM algorithm to take into account limited-angle acquisition. fSPECT images and preoperative SPECT/CT images were visualized as overlay on the live video of the patient or in a virtual reality view from the perspective of the tip of the gamma probe.
Pre OP PTH (pg/ml)
Post OP PTH (pg/ml)
A total of five parathyroid adenomas were successfully located in SPECT/CT. SPECT/CT shows the lesion in the anatomical context, thus helping the experienced surgeon in finding the lesions. It is however not easy to mentally transfer transsectional images on the patient's body surface. fSPECT allowed precise intraoperative detection of all adenomas, and successful parathyroidectomy was accomplished. The clinical utility of fSPECT in the operating room still has to be evaluated in further studies.
The 3-D overlay visualization of the adenomas on the live video of the patient can help to reduce invasiveness of parathyroidectomy and also improve accuracy. However, to maintain accurate localization of parathyroid adenomas, which depends on exact intraoperative superimposition of images onto the operative field, the situs has to remain rather static. This can only be reliably accomplished by using a retractor system which warrants minimal changes of the operative anatomy during surgical manipulation. A higher impact is expected from localizing ectopic parathyroid adenomas in the mediastinum, but this has still to be evaluated.
Since the scan must be repeated each time the patient is moved, several scans can extend the operation time.
In this preliminary study, we could demonstrate that localization of parathyroid adenoma is feasible using freehand SPECT technology. This approach has high potential to allow image-guided extirpation of parathyroid adenomas, thus bringing imaging into the operation room. Larger comparative studies are needed to evaluate the additional value.
We acknowledge the support from the Deutsche Forschungsgemeinschaft and the Open Access Publication Fund of the University of Muenster.
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