Fifty-three untreated patients with histologically confirmed Hashimoto's thyroiditis were divided into two groups according to the echogenicity of the thyroid. In 25 cases, the echogenicity of the thyroid was almost the same as or less than that of the adjacent muscles. Such cases were classified as group A. The other 28 cases were classified as group B. Mean T4 levels in group A were significantly lower than those in group B. In addition, the cases in group A had abnormally low T4 and abnormally high TSH more frequently than those in group B. In all cases in group A, there was severe degeneration and disappearance of thyroid follicles, whereas in most of the cases in group B, follicles of normal size were generally seen. Hypoechogenicity of the thyroid is a sign suggesting hypothyroidism and severe follicular degeneration.

Dynamic susceptibility-contrast MR imaging can provide useful hemodynamic information about intraaxial brain tumors that is not provided by standard MR imaging and therefore contributes to the differential diagnosis.

No abstract

To reduce the variability of the standardized uptake value (SUV) which is widely used to evaluate 2-[18F]fluoro-2-deoxy-d-glucose (FDG) uptake by neoplasms, net influx constant (Ki) was derived from SUV. The relationship Ki=SUV.kp.V0, where kp is the plasma clearance rate and V0 is the initial distribution volume of FDG, was utilized. A total of 71 plasma input functions were measured up to 60 min after intravenous injection of FDG in 55 patients and were analysed to obtain kp and V0. SUV and V0 were calculated based on either body weight or body surface area. To validate the Ki estimation, another group of eight patients with squamous cell carcinoma of the head and neck was included. Parametric images of the net influx constant were obtained by Patlak graphical analysis of dynamic positron emission tomography (PET) data and measured plasma input function. V0 based on body weight was 0.1627+/-0.0329 (ml/g) and showed a weak negative correlation with body weight (y=0.23356-0.00138x, r=0.591). V0 based on body surface area was 5540+/-871 (ml/m2) and had no significant correlation with body weight. kp at 50 min post injection was 0. 03272+/-0.00243 (1/min), and had no correlation with the plasma glucose concentration. A highly significant positive correlation was noted between true Ki and estimated Ki based on both body weight (y=0.0033+1.0371x, r2=0.897), and body surface area (y=0.0033+1. 0351x, r2=0.926). Ki, a better indicator of FDG uptake by tumour than SUV, is derivable non-invasively. Quantification of FDG uptake by Ki will aid standardization of diagnostic criteria of FDG PET oncology.

Double-echo dynamic magnetic resonance (MR) imaging was used to evaluate both vascularity and permeability of tissues simultaneously. Vascularity was evaluated on the basis of the T2*-shortening effect due to the intravascular fraction of the contrast agent and permeability on the basis of the T1-shortening effect due to the extravascular fraction. Meningioma was characterized on the basis of higher vascularity and neurinoma on the basis of higher permeability. The proposed method enables better tissue characterization.