Yuko Akashi

FDG-PET in infectious lesions: The detection and assessment of lesion activity

The usefulness of FDG-PET in the detection of infectious foci and the assessment of lesion activity was evaluated. The study covered 24 patients with 25 FDG-PET studies, including lesions of bacterial, tuberculous and fungal origins. The FDG uptake was determined by the lesion to muscle ratio (LMR) on the static images. The time activity curves (TACs) were classified into four patterns based on both the existence of an initial peak and a slope thereafter. A high FDG uptake was observed in 23 of 25 lesions (92%). Two lesions, in which no abnormal uptake was noted, included one in the healing stage and the other consisting of a cavity with a thin wall. The acute active lesions showed higher LMRs than the chronic active or healing lesions (mean ± SD: 9.8 ± 3.6, 3.6 ±1.8 and 4.3 ± 1.7, respectively, p < 0.05), and they could be approximately distinguished by an LMR of 6. The patterns of the TACs in acute or chronic active lesions were either an increase without an initial peak or a plateau, while those in the healing lesions demonstrated predominantly an increase with an initial sharp peak. Our results indicated that FDG-PET is clinically useful in the detection of the infection of miscellaneous microorganisms as well as in the assessment of lesion activity.

The usefulness of FDG positron emission tomography for the detection of mediastinal lymph node metastases in patients with non-small cell lung cancer : a comparative study with X-ray computed tomography

We evaluated the usefulness of fluorine-18-fluoro-2-deoxy-d-glucose positron emission tomography (FDG PET) in the detection of mediastinal lymph node metastases in patients with non-small cell lung cancer and then compared the findings with the results of X-ray CT by region based on the histological diagnoses. We examined 29 patients with non-small cell lung cancer. One hundred and thirty-two mediastinal lymph nodes were surgically removed and the histological diagnoses were confirmed. FDG PET images, including 146 mediastinal regions, were visually analysed and the mediastinal lymph nodes were scored as positive when the FDG uptake was higher than that in the other mediastinal structures. On the X-ray CT scans, any mediastinal lymph nodes with a diameter of 10 mm or larger were scored as positive. All three examinations were successfully performed on 71 regions. For FDG PET, we found a sensitivity of 76%, a specificity of 98% and an accuracy of 93%. On the other hand, for X-ray CT a sensitivity of 65%, a specificity of 87% and an accuracy of 82% were observed. A significant difference was observed in respect of both specificity and accuracy (P<0.05). Based on the above findings, FDG PET is suggested to be superior to X-ray CT when used for the detection of mediastinal lymph node metastases in patients with non-small cell lung cancer.

A clinical evaluation of FDG-PET to assess the response in radiation therapy for bronchogenic carcinoma

The clinical usefulness of FDG-PET in the prediction and assessment of response to radiation therapy in patients with bronchogenic carcinoma was evaluated. Thirty patients with untreated bronchogenic carcinoma were included in the study. All patients received FDG-PET before the initiation of radiation therapy, while 20 also received it after completing the therapy. The tumor to muscle ratio (TMR) was used as an index of the FDG uptake. The tumor response to therapy was classified as either a partial response (PR, n = 21) or no change (NC, n = 9) according to changes in the tumor size. Prognosis was made 6 months after the initiation of therapy, and was classified as either relapse (n = 19) or non-relapse (n = 9). The FDG uptakes both before and after therapy were compared with tumor response and prognosis. A high FDG uptake was noted in all 30 lesions before therapy. No significant differences in the uptake before therapy was observed according to the histological types nor T factors (UICC). The lesions with a higher uptake (TMR more than 7) responded better to therapy than those with a lower uptake (p < 0.05). The decrease in the uptake after therapy tended to be more prominent in the PR group than in the NC group. The rate of relapse was higher in lesions with a higher uptake before therapy (TMR more than 10) than in those with a lower uptake. The relapse group also showed a higher uptake after therapy than the non-relapse group. In addition, all 6 lesions showing a higher uptake (TMR more than 5) after therapy eventually relapsed (p < 0.05). Two lesions demonstrating a lower uptake both before and after therapy did not relapse, although no tumor regression due to the therapy was observed. These results indicate that FDG-PET plays a complementary role in both predicting and assessing the therapeutic response and prognosis in patients with bronchogenic carcinoma.

Striatal 18F-Dopa uptake and brain glucose metabolism by PET in patients with syndrome of progressive ataxia

Striatal 18F-Dopa uptake and brain glucose metabolism were studied by PET with 6-L-[18F]flurodopa and [18F]fluorodeoxyglucose in 11 patients with syndrome of progressive ataxia. Five of the 11 patients were diagnosed as having cerebellar cortical degeneration (CCD), including 3 with late cerebellar cortical atrophy and 2 with Holmes type hereditary ataxia while 6 demonstrated olivopontocerebellar atrophy (OPCA). The caudate and putaminal 18F-Dopa uptake ratios to the occipital cortex in CCD showed no significant difference from those in the controls. On the other hand, those with OPCA decreased as compared to the controls. In addition, the cerebellar glucose metabolism in CCD decreased as compared to the controls, while that in the brainstem showed no significant decrease from the controls. The glucose metabolic rates both in the cerebellar hemisphere and in the brainstem in the OPCA patients decreased compared to the controls. The cerebral cortical, striatal and thalamic glucose metabolisms were normal in both the CCD and OPCA in groups. The appearance of a decreased glucose metabolism in the cerebellum is considered to be relevant in the genesis of cerebellar ataxia, even though their underlying diseases were different from each other. The differences in the glucose metabolism of the brainstem and in the nigrostriatal presynaptic dopaminergic function between CCD and OPCA as assessed by PET may be caused by differences in the pathophysiological mechanism between CCD and OPCA, and those differences appear to be useful when making a differential diagnosis of CCD and OPCA.

Cerebellar vascular response to acetazolamide in crossed cerebellar diaschisis: a comparison of99mTc-HMPAO single-photon emission tomography with15O-H2O positron emission tomography

Various observations on the cerebellar vasoreactivity in crossed cerebellar diaschisis (CCD) have previously been reported. The purpose of this study is to clarify the difference between oxygen-15 H2O positon emission tomographic (PET) and technetium-99m hexamethylpropylene amine oxime (HMPAO) single-photon emission tomograph (SPET) findings in CCD and to evaluate the effect of the absolute values of the cerebellar blood flow as measured by15O-H2O PET on the99mTc-HMPAO SPET findings. The subjects comprised 15 patients with a supratentorial infarct and CCD. The cerebellar blood flow increased by about 40% at 5 and 20 min after acetazolamide i.v. on both the CCD and the non-CCD side, as measured by 150-1120 PET. The percentage differences in cerebellar blood flow between the CCD and the non-CCD side were −22.3%±5.7% in the resting state, −19.6%±6.4% at 5 min after acetazolamide i.v. and 21.5%±6.7% at 20 min after acetazolamide i.v., as measured by15O-H2O PET, while they were −10.6%±5.5% in the resting state and −5.6%±5.1% at 5 min after acetazolamide i.v., as measured by99mTc-HMPAO SPET. After Lassens linearization correction, the latter two measurements were −16.2%±7.7% and −9.6%±8.9%, respectively. The effect of acetazolamide did not differ between the CCD and the non-CCD side in15O–H2O PET, while a greater response on the CCD side was observed in99mTc-HMPAO SPET, even after Lassens linearization correction. It is concluded that acetazolamide HMPAO SPET may overestimate the cerebellar vascular response on the CCD side (or underestimate it on the non-CCD side).

Evaluation of Clinical Usefullness of Myocardial Perfusion Imaging with Tetrofosmin in Patients with Ischemic Heart Disease. Comparison with 201Tl SPECT.

We evaluated the clinical usefulness of 99mTc-1, 2-bis [bis (2-ethoxyethyl) phosphino] ethane (tetrofosmin) and compared it with 201Tl. The subjects consisted of 12 patients including 8 patients with old myocardial infarction (OMI), 2 with effort angina, one with stable angina and one with myocarditis. The tetrofosmin SPECT images were obtained during exercise and at rest. The quality of tetrofosmin SPECT images was equal or slightly superior to that of 201Tl. And the sensitivity, specificity and accuracy of tetrofosmin for the detection of coronary stenosis and/or obstruction were equal to that of 201Tl. We conclude that tetrofosmin is useful in the diagnosis of ischemic heart disease.