Clinical Application of PET/CT Fusion Imaging for Three-Dimensional Myocardial Scar and Left Ventricular Anatomy during Ventricular Tachycardia Ablation

Background: Image integration has the potential to display three-dimensional (3D) scar anatomy and facilitate substrate characterization for ventricular tachycardia (VT) ablation. However, the current generation of clinical mapping systems cannot display 3D left ventricle (LV) anatomy with embedded 3D scar reconstructions or allow display of border zone and high-resolution anatomic scar features.
Objective: This study reports the first clinical experience with a mapping system allowing an integrated display of 3D LV anatomy with detailed 2D/3D scar and border zone reconstruction.
Methods: Ten patients scheduled for VT ablation underwent contrast-enhanced computed tomography (CT) and Rubidium-82 perfusion/F-18 Fluorodeoxyglucose metabolic Positron Emission Tomography (PET) imaging to reconstruct 3D LV and scar anatomy. LV and scar models were co-registered using a 3D mapping system and analyzed with a 17-segment model. Metabolic thresholding was used to reconstruct the 3D border zone. Real-time display of CT images was performed during ablation.
Results: Co-registration (error 4.3 ± 0.7 mm) allowed simultaneous visualization of 3D LV anatomy and embedded scar and guided additional voltage mapping. Segments containing homogenous or partial scar correlated in 94.4% and 85.7% between voltage maps and 3D PET scar reconstructions, respectively. Voltage-defined scar and normal myocardium had relative FDG uptakes of 40 ± 13% and 89 ± 30% (P < 0.05). The 3D border zone correlated best with a 46% metabolic threshold. Real-time display of registered high-resolution CT images allowed the simultaneous characterization of scar-related anatomic changes.
Conclusion: Integration of PET/CT reconstruction allows simultaneous 3D display of myocardial scar and border zone embedded into the LV anatomy as well as the display of detailed scar anatomy. Multimodality imaging may enable a new image-guided approach to substrate-guided VT ablation.     

Association of Thyroid Carcinoma with Malignant Lymphoma

Radiation-associated thyroid carcinoma is of clinical importancein modern radiation therapy of both Hodgkin's disease (HD) andnon-Hodgkin's lymphoma (NHL), because anatomically the thyroidis often in the radiation field. We have reviewed the recordsof HD and NHL patients seen at Roswell Park Memorial Institute(RPMI) between 1910 and 1960 to determine associated occurrenceof thyroid cancer. Radiation therapy was the major therapeuticmodality with the occasional use of single agent chemotherapywith nitrogen mustard, triethylene melamine (TEM), chlorambuciland prednisone. There were 519 patients with HD and 863 withNHL. The thyroid glands of 439 (84%) HD and 544 (63%) NHL patientswere included in the field of radiation. The mean age of patientswith HD was 39 yr while for those with NHL, it was 53 yr. Themean survival in HD was 4.2 yr and in NHL 3.8 yr. There werethree cases of thyroid cancer among the HD patients occurring31, 44 and 48 yr, respectively, after radiation therapy. Whencompared with the number of thyroid cancers expected to develop,the incidence was significantly greater (p < 0.005). In contrast,three NHL patients were found to have thyroid cancer at thetime of surgery or postmortem examination. This number is againgreater than expected in such a population (p < 0.005); however,in only two cases could the cancer be considered as a sequelato NHL treatment. In all three cases the cancer turned out tobe subclinical thyroid carcinoma, incidentally found at surgeryor autopsy. One of the patients is still alive without evidenceof either disease. The reason for this difference between patientswith HD and NHL treated with a similar principle is unclear.Some of the factors contributing to this difference may include:the younger age of HD patients at diagnosis; the longer survivalof patients with HD as compared with those with NHL; differencesin the sites of radiation and type of treatment given; and possibledifferences in immunological status between the two groups. ²Present addresses: 211 Owen Drive, Fayetteville, North Carolina,28304, U.S.A. ⁴Present addresses: 212 West 18th Street, Hopkinsville, Kentucky,42240, U.S.A. ⁵Present addresses: St. Francis Hospital, Park Avenue, Memphis,Tennessee, 38119, U.S.A ⁷Present addresses: Vassar Brothers Hospital, Poughkeepsie,NewYork, 12601, U.S.A.