Double-injection method for sequentially measuring cerebral blood flow with N-isopropyl-(123I)p-iodoamphetamine

Quantitative assessment of cerebral hemodynamics using single photon emission computed tomography with venous blood sampling

OBJECTIVE

Quantitative cerebral blood flow (CBF) measured by single photon emission computed tomography (SPECT) with arterial blood sampling is one of the most reliable methods to assess the hemodynamics in individual patients. SPECT with venous blood sampling is less invasive. The present study compared the measurement of CBF using N-isopropyl-p-(iodine-123)-iodoamphetamine SPECT with venous blood sampling and with arterial blood sampling in patients with major cerebral artery occlusive disease.

METHODS

Two normal subjects and 14 patients with major cerebral artery occlusive disease underwent SPECT with arterial and venous blood sampling. The microsphere method was used for quantitative SPECT imaging. Whole brain radioactivity was corrected when the detectors rotated in the forward direction (F1-F7). Venous sampling was performed 30min after radiotracer injection. Arterial blood radioactivity was estimated by multiple regression analysis from these parameters. The cerebrovascular reactivity to acetazolamide was also measured.

RESULTS

Multiple regression analysis established the following formula:(where Ca10 is the arterial blood radioactivity at 10min, F1-F7 are the whole brain radioactivity in the forward direction, Cv30 is the venous blood radioactivity at 30min). Mean CBF values were 32.2±6.6ml/100g/min for measured arterial radioactivity and 42.2±7.8ml/100g/min for calculated arterial radioactivity based on venous radioactivity.

CONCLUSIONS

The present modified method of calculating quantitative CBF from whole brain and venous blood radioactivities correlated well with values determined with arterial blood radioactivity.

Measurement of regional cerebral blood flow with123I-IMP using one-point venous blood sampling and causality analysis: Evaluation by comparison with conventional continuous arterial blood sampling

OBJECTIVE

Arterial input function represents the delivery of intravascular tracer to the brain. The optimal setting of this function is essential for measuring regional cerebral blood flow (rCBF) based on the microsphere model using N-isopropyl-4-[123I]iodoamphetamine (123I-IMP), in which the arterial 123I-IMP concentration (integral value) during the initial 5 min is usually applied. We developed a novel method in which the arterial 123I-IMP concentration is estimated from that in venous blood samples.

METHODS

Brain perfusion SPECT with 123I-IMP was performed in 110 patients with disorders of the central nervous system. A causality analysis determined the relationship between various SPECT parameters and the ratio of the octanol-extracted arterial radioactivity concentration during the first 5 min (Caoct) to the octanol-extracted venous radioactivity concentration at 27 min after an intravenous injection of 123I-IMP (Cvoct). The Caoct/Cvoct value was estimated using various SPECT parameters and compared with the directly measured value.

RESULTS

The measured and estimated values of Caoct/ Cvoct (r = 0.856, n = 50) closely correlated when the following 7 parameters were included in the regression formula: radioactivity concentration in venous blood sampled at 27 min (Cv), Cvoct, Cvoct/Cv, and 4 parameters related to cerebral tissue accumulation that were measured using a four-head gamma camera 5 and 28 min after 123I-IMP injection. Furthermore, the rCBF values obtained using the input function estimated by this method also closely correlated with the rCBF values measured using the continuous arterial blood sampling (r = 0.912, n = 180).

CONCLUSION

These results suggest that this method would serve as a convenient and less invasive method of rCBF measurement in the clinical setting.

A simplified double-injection method to quantify cerebral blood flow and vascular reserve using iodine-123 IMP-SPECT

We developed and evaluated a simplified double-injection method for iodine-123 N-isopropyl-p-iodoamphetamine (IMP) to quantify regional cerebral blood flow (rCBF) twice in a single SPECT session. The method enabled rapid calculations of rCBF with five 10-minute SPECT scans, a fixed distribution volume (Vd), and one-point arterial blood sampling to calibrate a standard input function (SIF).

METHODS

Sixty neurological patients were examined to measure rCBF twice in a single session of IMP-SPECT. Patients underwent frequent arterial blood sampling with two injections of IMP and acetazolamide challenge. We generated the SIF and determined the optimal Vd and calibration time (t(cal)) for the SIF in 30 patients. Validities of the fixed t(cal) and Vd were assessed in the remaining 30 patients. Simulation studies were also performed to evaluate the error sensitivity of the method.

RESULTS

The optimal t(cal) and Vd were 34 min and 30 ml/ml, respectively. The method was robust in rCBF calculation with noisy SPECT data and yielded rCBF with negligible bias and acceptable errors compared with those obtained by the double-injection method previously reported.

CONCLUSION

The method can be applied to measure rCBF twice in a single SPECT session more easily and less invasively.