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Attenuation correction of PET cardiac data with low-dose average CT in PET/CT

We proposed a low-dose average computer tomography (ACT) for attenuation correction (AC) of the PET cardiac data in PET/CT. The ACT was obtained from a cine CT scan of over one breath cycle per couch position while the patient was free breathing. We applied this technique on four patients who underwent tumor imaging with F18-FDG in PET/CT, whose PET data showed high uptake of F18-FDG in the heart and whose CT and PET data had misregistration. All four patients did not have known myocardiac infarction or ischemia. The patients were injected with 555-740MBq of F18-FDG and scanned 1h after injection. The helical CT (HCT) data were acquired in 16s for the coverage of 100cm. The PET acquisition was 3min per bed of 15cm. The duration of cine CT acquisition per 2cm was 5.9s. We used a fast gantry rotation cycle time of 0.5s to minimize motion induced reconstruction artifacts in the cine CT images, which were averaged to become the ACT images for AC of the PET data. The radiation dose was about 5mGy for 5.9s cine duration. The selection of 5.9s was based on our analysis of the respiratory signals of 600 patients; 87% of the patients had average breath cycles of less than 6s and 90% had standard deviations of less than 1s in the period of breath cycle. In all four patient studies, registrations between the CT and the PET data were improved. An increase of average uptake in the anterior and the lateral walls up to 48% and a decrease of average uptake in the septal and the inferior walls up to 16% with ACT were observed. We also compared ACT and conventional slow scan CT (SSCT) of 4s duration in one patient study and found ACT was better than SSCT in depicting average respiratory motion and the SSCT images showed motion-induced reconstruction artifacts. In conclusion, low-dose ACT improved registration of the CT and the PET data in the heart region in our study of four patients. ACT was superior than SSCT for depicting average respiration motion in a patient study.

Sentinel node mapping in vulvovaginal melanoma using SPECT/CT lymphoscintigraphy

We report 2 cases of vulvovaginal melanoma in which sentinel node mapping, performed using Tc-99m filtered sulfur colloid SPECT/CT lymphoscintigraphy, added important information to that provided by planar imaging and played a critical role in surgical planning and subsequent management. In the first case, lymphoscintigraphy planar imaging showed only foci of tracer uptake in the right groin and an equivocal focus in the left groin. SPECT/CT precisely localized these radioactive foci to the right and left inguinal sentinel nodes. The patient then underwent bilateral inguinal sentinel node sampling. In the second case, F-18 FDG PET/CT performed prior to lymphoscintigraphy demonstrated a moderately FDG-avid right inguinal lymph node that was indeterminate in nature. SPECT/CT revealed this lymph node to be a radioactive sentinel lymph node that was seen in the right groin on planar imaging. The patient then underwent right inguinal sentinel node sampling. Because pathologic study showed metastasis to the sentinel node, a planned pelvic exenteration was canceled, and the patient was referred for systemic treatment. Preoperative SPECT/CT lymphoscintigraphy is ideal for mapping the unpredicted lymphatic drainage pathways within the complex pelvic anatomy and this technique may also be used in the preoperative workup of other gynecologic malignancies.

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

Lymphoscintigraphy is a nuclear medicine procedure that is used to detect sentinel lymph nodes (SLNs). This project sought to investigate fusion of planar scintigrams with CT topograms as a means of improving the anatomic reference for the SLN localization. Heretofore, the most common lymphoscintigraphy localization method has been backlighting with a 57Co sheet source. Currently, the most precise method of localization through hybrid SPECT/CT increases the patient absorbed dose by a factor of 34 to 585 (depending on the specific CT technique factors) over the conventional 57Co backlighting. The new approach described herein also uses a SPECT/CT scanner, which provides mechanically aligned planar scintigram and CT topogram data sets, but only increases the dose by a factor of two over that from 57Co backlighting. Planar nuclear medicine image fusion with CT topograms has been proven feasible and offers a clinically suitable compromise between improved anatomic details and minimally increased radiation dose.

Optimal 57Co flood source activity and acquisition time for lymphoscintigraphy localization images

We evaluated different 57Co flood source activities and acquisition times to obtain an optimal localization image for breast lymphoscintigraphy that would adequately outline the body and allow detection of nodes seen on the emission scan while minimizing unnecessary radiation exposure to the patient. Methods: An anthropomorphic thorax breast phantom representing an average-size patient was used to simulate nodes on a breast lymphoscintigraphy scan. The activities in the nodes at the time of acquisition ranged from 37 to 185 kBq (1–5 μCi). Four experiments were performed, consisting of 10-min emission and 3-min localization images. Anterior, posterior, and right and left lateral views of the thorax phantom were acquired, using each of 5 different 57Co flood sources with activities ranging from 37 to 269 MBq (1.0–7.26 mCi). Ten 1-min localization images for each source were acquired and compared for quality. Three-minute localization images for 2 phantom thicknesses of 10 and 20 cm were acquired to determine the contrast-to-noise ratio for each 57Co source. The total exposure was measured using an ion chamber survey meter. Results: All sources allowed visualization of the lymphatic nodes in acquisitions as short as 3 min. Images using the 126-MBq (3.41-mCi) source demonstrated an adequate body outline along with visualization of all nodes seen on the emission image. The 37-MBq (1.0-mCi) source did not provide sufficient definition of the body outline, whereas the hotter sources decreased node visualization by increasing the background around the nodes at the same time that they increased the patient exposure. Node activity of 37 kBq (1 μCi) became undetectable on the anterior localization images yet was still visible on the lateral image because of greater attenuation of 57Co photons. The estimated dose rate from the 57Co sheet sources was 0.641 μSv/MBq/h. Conclusion: Acquiring a 3-min localization scan using a 126-MBq (3.41-mCi) source provided the best combination of clear-body outline and visualization of all nodes seen on the emission image. The estimated dose to the patient from the 126-MBq (3.41-mCi) sheet source was very low (8.7 μSv for unilateral and 13.1 μSv for bilateral). Node detectability decreased in localization images acquired using 57Co sources of higher activity. This effect would be more pronounced in lymphoscintigrams of thin patients compared with those of patients of average thickness.

Qualitative and quantitative comparison of gated blood pool single photon emission computed tomography using low-energy high-resolution and SMARTZOOM collimation.

Objective The aim of this study was to assess the feasibility of IQ-SPECT gated blood pool (MUGA) under conditions of decreased scan time (ST). Patients and methods Ten patients underwent routine 26-min, two-view planar, followed by LEHR and IQ-SPECT MUGA, on a Siemens dual-head Symbia scanner. Six ‘back and forth’ 4-min SPECT scans were summed into 4-, 8-, 12-, 16-, 20-, and 24-min equivalent scans, and reconstructed iteratively (IQ-SPECT and LEHR) and with FBP (LEHR). Uniformity, contrast, and wall motion were scored on a five-point scale. Linear regressions of left ventricular (LV) ejection fraction (EF) were performed between FBP, Flash 3D, and IQ-SPECT versus planar and Flash 3D and IQ-SPECT versus FBP. Agreement tables between Flash 3D and IQ-SPECT versus FBP LV EF were generated using a normal versus cardiotoxicity threshold of 50%. Results IQ-SPECT had the best scores for all STs, and 4, 8, and 16 min IQ-SPECT were judged to be similar to 24-min LEHR FBP, Flash 3D, and planar, respectively. The average LV EF correlation coefficients were 0.69, 0.71, and 0.63 between IQ-SPECT, Flash 3D, and FBP versus planar, respectively; 0.70 between IQ-SPECT and FBP; and 0.88 between Flash 3D and FBP, and all were statistically significant (P<0.05), except for 16-min FBP LEHR versus planar. Agreement tables showed diagnostic equivalence of IQ-SPECT, Flash 3D, and FBP. Conclusion These preliminary results suggest that IQ-SPECT is equivalent to LEHR Flash 3D and FBP for MUGA SPECT, and better at reduced ST. A larger patient population study is necessary for a more definitive assessment.

False-positive pericardial effusion due to breast attenuation on equilibrium radionuclide angiocardiography.

Equilibrium radionuclide angiocardiography (ERNA) scans are used to evaluate left ventricular function and pericardial anatomy. A photopenic “U-halo” around the cardiac blood pool in the left anterior oblique (LAO) view is commonly seen with pericardial effusion. We describe findings of false-positive pericardial effusion due to breast attenuation in cancer patients. Methods: Several cases that demonstrated the photopenic U-halo in the LAO view did not have true pericardial effusion. The patients’ breast size and how far the breast sagged in reference to the heart silhouette were visually observed in topograms. The oblique tilt position was evaluated to determine the effect it may have in creating the photopenic U-halo. A unique ERNA case demonstrating collateral vessels bilaterally in the breasts was used as a reference marker image to determine the effect of a slightly more anterior versus left lateral oblique tilt in the LAO view. Results: Large breasts can overlie the heart in the LAO projection. The overlying breast can cause the appearance of pericardial effusion in the resulting image by attenuating tissues surrounding the heart. The positioning of the breast also affected the appearance of the photopenic halo. A patient with breast implants who had more upright breasts demonstrated a photopenic area anterior to the left ventricle, whereas a large breast that sagged more laterally demonstrated no photopenic area. Conclusion: Patients with large breasts may show a photopenic U-halo in the LAO view dependent on how far the breast sags in reference to the heart silhouette and on the positioning of the oblique tilt. The anterior image should be used to distinguish breast attenuation from a photopenic area surrounding the heart. If both the anterior view and the LAO view demonstrate the U-halo, acquiring another view with a slightly more anterior or lateral oblique position will demonstrate any inconsistency in the photopenic area, thereby excluding a diagnosis of pericardial effusion.