Hybrid Modality Fusion of Planar Scintigrams and CT Topograms to Localize Sentinel Lymph Nodes in Breast Lymphoscintigraphy: Technical Description and Phantom Studies

Comparison of lymphoscintigraphy and single photon emission computed tomography with computed tomography (SPECT/CT) for sentinel lymph node detection in endometrial cancer

BACKGROUND

Endometrial cancer is the most common gynecologic cancer, and lymph node metastasis is one of the most important prognostic factors. Increasing evidence shows that sentinel lymph node (SLN) mapping is an effective alternative to comprehensive lymphadenectomy. Single photon emission CT with computed tomography (SPECT/CT) is associated with a high SLN detection rate.

OBJECTIVE

To compare the clinical efficacy of SPECT/CT with that of lymphoscintigraphy in detecting SLNs in patients with endometrial cancer.

METHODS

Between May 2014 and October 2018, 151 patients with endometrial cancer were enrolled in this study at the Department of Obstetrics and Gynecology of the Kagoshima University Hospital. Inclusion criteria were patients with endometrial cancer, older than 18 years, and with pre-operative International Federation of Gynecology and Obstetrics (FIGO) staging of I and II. All patients underwent pre-operative CT, and patients with suspected peritoneal dissemination and lymph node metastasis were excluded from this study. Pelvic SLNs were detected by injection of tecnetium-99m-labeled phytate into the uterine cervix. The number and locations of SLNs detected using lymphoscintigraphy and SPECT/CT were evaluated. JMP software (version 14, SAS Institute Inc., Cary, North Carolina, USA) was used for statistical analysis.

RESULTS

A total of 151 patients who underwent pre-operative lymphoscintigraphy and SPECT/CT were included in the study. The median age was 57 years (range 24-79), and the median body mass index was 24.3 kg/m² (range 16-40). The final pathology was as follows: 135 (89%) endometrioid carcinoma, 11 (7%) serous carcinoma, one (1%) clear cell carcinoma, and four (3%) other histotypes. Based on SPECT/CT, 204 pelvic SLNs were detected. The bilateral pelvic SLN detection rate was better for SPECT/CT (43% (65/151)) than for lymphoscintigraphy (32% (48/151)) (p<0.0001). The overall pelvic SLN detection rate (at least one pelvic SLN detected) was also better with SPECT/CT (77% (16/151)) vs lymphoscintigraphy (68% (102/151)) (p<0.0001). The distribution of SLN locations detected using SPECT/CT was as follows: external iliac, 91 (45%); obturator, 61 (30%); common iliac, 28 (14%); internal iliac, 19 (9%); para-aortic, 2 (1%); parametrium, 2 (1%), and presacral, 1 (1%). The SLN detection rate using SPECT/CT was significantly worse in patients of advanced age (p<0.0001).

DISCUSSION

Overall and bilateral SLN detection rate was better with SPECT/CT than with lymphoscintigraphy in patients with stage I/II endometrial cancer.

Estimation of radioactivity in single-photon emission computed tomography for sentinel lymph node biopsy in a torso phantom study

OBJECTIVE

The number of lymph nodes to be removed is determined from residual counts. Advance estimation of residual radioactivity in lymphatic nodes before a biopsy is useful for reducing surgical operation time. The purpose of this study was to estimate the total radioactivity of a small hotspot in single-photon emission computed tomography (SPECT) of a torso phantom.

METHODS

A cross-calibration study was performed to convert counts in SPECT images to radioactivity. A simulation study was performed to estimate the size of the volume of interest (VOI) covering a hotspot corrupted with full-width at half-maximum between 8 and 16 mm. The estimation of total radioactivity was validated in a torso phantom study using small sources.

RESULTS

True radioactivity was approximately equal to integrated values of hotspots using the VOI with a diameter of 40 mm in our simulation study. The difference was less than 18% in cases of more than 9.4 kBq.

CONCLUSION

The total radioactivity in small sources simulating a typical sentinel node was estimated from SPECT images using a VOI of 40 mm in a torso phantom study. Because the difference from actual values was less than 10% on average when radioactivities were more than 9.4 kBq, the total radioactivity of a lymph node can be estimated in a clinical examination.

Radio-guided sentinel lymph node identification by lymphoscintigraphy fused with an anatomical vector profile: clinical applications

OBJECTIVE

To develop a method to fuse lymphoscintigraphic images with an adaptable anatomical vector profile and to evaluate its role in the clinical practice.

METHODS

We used Adobe Illustrator CS6 to create different vector profiles, we fused those profiles, using Adobe Photoshop CS6, with lymphoscintigraphic images of the patient. We processed 197 lymphoscintigraphies performed in patients with cutaneous melanomas, breast cancer or delayed lymph drainage.

RESULTS

Our models can be adapted to every patient attitude or position and contain different levels of anatomical details ranging from external body profiles to the internal anatomical structures like bones, muscles, vessels, and lymph nodes. If needed, more new anatomical details can be added and embedded in the profile without redrawing them, saving a lot of time. Details can also be easily hidden, allowing the physician to view only relevant information and structures. Fusion times are about 85 s. The diagnostic confidence of the observers increased significantly. The validation process showed a slight shift (mean 4.9 mm).

CONCLUSIONS

We have created a new, practical, inexpensive digital technique based on commercial software for fusing lymphoscintigraphic images with built-in anatomical reference profiles. It is easily reproducible and does not alter the original scintigraphic image. Our method allows a more meaningful interpretation of lymphoscintigraphies, an easier recognition of the anatomical site and better lymph node dissection planning.

Detection of Sentinel Lymph Nodes in Gynecologic Tumours by Planar Scintigraphy and SPECT/CT

Objective: Assess the role of planar lymphoscintigraphy and fusion imaging of SPECT/CT in sentinel lymph node (SLN) detection in patients with gynecologic tumours.

Material and Methods: Planar scintigraphy and hybrid modality SPECT/CT were performed in 64 consecutive women with gynecologic tumours (mean age 53.6 with range 30-77 years): 36 pts with cervical cancer (Group A), 21 pts with endometrial cancer (Group B), 7 pts with vulvar carcinoma (Group C). Planar and SPECT/CT images were interpreted separately by two nuclear medicine physicians. Efficacy of these two techniques to image SLN were compared.

Results: Planar scintigraphy did not image SLN in 7 patients (10.9%), SPECT/CT was negative in 4 patients (6.3%). In 35 (54.7%) patients the number of SLNs captured on SPECT/CT was higher than on planar imaging. Differences in detection of SLN between planar and SPECT/CT imaging in the group of all 64 patients are statistically significant (p<0.05). Three foci of uptake (1.7% from totally visible 177 foci on planar images) in 2 patients interpreted on planar images as hot LNs were found to be false positive non-nodal sites of uptake when further assessed on SPECT/CT. SPECT/CT showed the exact anatomical location of all visualised sentinel nodes.

Conclusion: In some patients with gynecologic cancers SPECT/CT improves detection of sentinel lymph nodes. It can image nodes not visible on planar scintigrams, exclude false positive uptake and exactly localise pelvic and paraaortal SLNs. It improves anatomic localization of SLNs.

Conflict of interest:None declared.

Hybrid imaging in planar scintigraphy: new implementations and historical precedents

Fusion of tomographic radionuclide studies with anatomical examinations has become standard practice in positron emission tomography (PET) and single photon emission computed tomography (SPECT) imaging. Nonetheless, fusion of planar scintigraphic images with an anatomical modality remains distinctly uncommon, although methods to do so have appeared sporadically in the literature during the past 2 decades. In this article we review several techniques that have been used to combine planar scintigraphic images with radiographs and visual (photographic) images. Rigid or affine transformations have been performed to co-register the planar images with each other using custom, commercial, or public domain software. Display of the hybrid images has been achieved primarily with nonselective color-fusion methods. Promising efforts are underway to develop a technique of fusing planar lymphoscintigraphic images with CT topograms (scout images) obtained on the SPECT-CT camera in a manner that compensates for position-dependent variation in magnification that affects the CT scout. An advantage of this approach is that both of the component images are acquired on the same gantry, without need for repositioning of the patient. It is instructive to note that techniques of fusing rectilinear scans with radiographic and visual images were first developed more than 50 years ago. The revisiting of these methods after many decades reflects a fundamental need for spatial orientation in nuclear medicine that fusion imaging can also bring to planar scintigraphic studies.