Hybrid SPECT/CT Imaging in the Management of Differentiated Thyroid Carcinoma

Differentiated thyroid cancer (DTC) has a good prognosis overall; however, lifelong follow-up is required for many cases. Radioiodine planar imaging with iodine-123 (I-123) or radioiodine-131 (I-131) remains the standard in the follow-up after initial surgery and ablation of residual thyroid tissue using I-131 therapy. Radioiodine imaging is also used in risk-stratifying and for staging of thyroid cancer, and in long-term follow-up. Unfortunately, the lack of anatomical detail on planar gamma camera imaging and superimposition of areas presenting with increased radioiodine uptake can make accurate diagnosis and localization of radioiodine-avid metastatic disease challenging, leading to false positive results and potentially to over-treatment of patients. Hybrid SPECT/CT allows precise anatomical localization and superior characterization of foci of increased tracer uptake when compared to planar imaging. This, in turn, allows the differentiation of pathological and physiological uptake, increasing the accuracy of image interpretation and ultimately improving the accuracy of DTC staging and subsequent patient management. In this review, we look at the unique and emerging role that SPECT/CT plays in the management of DTC, illustrated by examples from our own clinical practice.

Prediction of cardiac events in patients having left bundle-branch block with/without chest pain using dipyridamole technetium-99m-sestamibi myocardial perfusion imaging

OBJECTIVE

To determine the prognostic value of myocardial perfusion scintigraphy with dipyridamole stress in patients with preexisting left bundle-branch block (LBBB) with or without chest pain.

SUBJECTS AND METHODS

Seventy-six patients, mean age 53 +/- 10 years, with preexisting LBBB underwent technetium-99m-sestamibi perfusion imaging with dipyridamole infusion protocol (0.56 mg/kg). Stress and rest single photon emission computed tomography (SPECT) images were interpreted by consensus of 2 experienced nuclear medicine physicians and classified as low-risk scans (normal myocardial perfusion scan, small reversible/small fixed defect) and high-risk scans (large, severe, fixed or reversible defect and dilated left ventricle cavity). The patients were followed up for 24 +/- 8 months and occurrences of hard cardiac events (infarction or cardiac death) were noted.

RESULTS

Of the 76 patients, 52 (68%) had low-risk scans and the remaining 24 (32%) had high-risk scans. In the low-risk group, 1 (1.9%) cardiac death and 2 (3.8%) cases of nonfatal myocardial infarction occurred, while in the high-risk group, 5 (20.8%) suffered cardiac death, and 3 (12.5%) nonfatal myocardial infarction. Overall survival rate was 98.1% in the low-risk group compared with 79.2% in the high-risk group with a significant difference of p = 0.034. Negative predictive value of normal myocardial perfusion scintigraphy for the occurrence of death was 100%. No significant difference in survival rate among patients with or without chest pain (p = 0.31) was observed.

CONCLUSIONS

Myocardial perfusion imaging with dipyridamole provided important prognostic information in patients with LBBB; it was useful in stratifying the patients according to cardiovascular morbidity and mortality, and would thus allow the clinician to provide early treatment especially in the high-risk category.

Chest wall recurrence of breast cancer demonstrated on 99mTc-MIBI scintimammography

BACKGROUND

The mastectomy site is usually assessed by clinical examination and ultrasonography for recurrence of breast cancer, although post-surgical and radiotherapy changes limit the accuracy of these methods. MRI has been used successfully but it remains an expensive modality and may not be readily available. Scintimammography is an alternative method which has the advantage of not being affected by post-operative morphological changes.

AIM

To evaluate the usefulness of planar Tc-MIBI scintimammography and supine Tc-MIBI SPECT in the detection of chest wall recurrence post-mastectomy.

METHODS

The study population comprised of 26 patients (mean age, 47.15 years; median age 47 years; age range, 22-77 years) with suspected chest wall recurrence of breast cancer on clinical examination. All patients received a 740-1000 MBq bolus i.v. injection of Tc-MIBI preferably in the pedal vein. At 5-10 min post-injection planar images were obtained in the prone lateral and supine anterior positions using a double-head gamma camera. After planar imaging supine SPECT was performed (64 projections, 64x64 matrix, 30 s.frame). MIBI uptake was scored as follows: 1 = normal uptake (compared with contralateral side); 2 = focal low uptake (equivocal); and 3 = focal high uptake (positive). All patients underwent excision biopsy or FNAC for tissue diagnosis. FNAC was considered sufficient if unequivocally positive.

RESULTS

For the 26 patients, planar scintimammography was found true positive in 14 and true negative in seven. The sensitivity, specificity, positive predictive value, negative predictive value and accuracy were 78%, 87.5%, 93%, 64% and 81%, respectively (P<0.001). SPECT showed a significantly higher overall sensitivity than planar imaging (89% vs. 78%; P<0.001). SPECT and planar imaging showed the same specificity (87.5%). SPECT showed a significantly higher negative predictive value and accuracy than planar imaging (78% vs. 64% and 88% vs. 81%, respectively; P<0.05).

CONCLUSION

Scintimammography is a reliable diagnostic tool and appears accurate in the detection of chest wall recurrence. SPECT shows high positive predictive value and aids in the diagnosis of the chest wall recurrence with greater confidence.

Role of 99mTc-MIBI scintimammography and X-ray mammography in the diagnosis of locoregional recurrence of breast cancer

OBJECTIVE

To evaluate the utility of Tc- MIBI scintimammography in the loco-regional recurrence of breast cancer and its comparison with mammography.

METHODS

The study population comprised of 33 subjects (mean age, 44.9 +/- 14.1 years); evaluated for suspected loco-regional recurrence of breast cancer on clinical examination. All subjects received a 740-1000 MBq bolus IV injection of 99mTc-MIBI preferably in pedal vein. At 5-10 min and 60-90 min post injection planar images were obtained in prone lateral and supine anterior position using double head gamma camera. MIBI uptake was scored as follows: 1: as normal uptake (compared with contralateral side); 2: focal low intense uptake (equivocal); 3: focal high intense uptake (positive). Mammography was performed by two standard views of cranio-caudal and mediolateral oblique in 26 patients. All patients had either excision biopsy or fine needle aspiration cytology (FNAC) for tissue diagnosis.

RESULTS

Out of 33 patients, 21 had confirmed as recurrence on hiostopathology/cytology. Scintimammography was found true positive in 18 and true negative in 11 patients. The sensitivity, specificity, positive predictive value, negative predictive value and accuracy were 85.7%, 91.7%, 94.7%, 78.6% and 87.8% respectively. In comparison, mammography was true positive in 9 and true negative in 6 patients with sensitivity of 52.9%, specificity, 66.7%, PPV 75%, NPV 42.9% and accuracy 57.7%.

CONCLUSION

Scintimammography has better diagnostic accuracy than mammography in the detection of loco-regional recurrence of breast cancer.

Assessment of viable myocardium by nitrate augmented 99mTc MIBI myocardial perfusion imaging

OBJECTIVE

To determine the efficacy of 99mTcMIBI with nitrate administration for the detection of viable myocardium in patients with MI.

METHODS

Thirty-five patients (31 men, 4 women; mean age 51.91 +/- 8.86 years, median = 50) with previous history of myocardial infarction (with mean duration of 11.50 +/- 11.4, median =4 months after MI) were included in the study. All patients underwent baseline rest and Nitroglycerine 99mTcMIBI myocardial perfusion imaging (2 day protocol). Fifteen out of 34 patients were also submitted for rest and redistribution TI-201 imaging (3 day protocol). The data were reconstructed in transaxial slices and then reoriented into short, vertical long and horizontal long axis slices. The images were divided into seven different segments for qualitative as well as semi quantitative analysis. The images were interpreted by two independent observers. The segments with tracer activity of more than 55% as compared to maximum, were considered as viable.

RESULTS

In the baseline study with 99mTcMIBI, 168/245 (68.57%) were viable segments and these were increased to 197 (80.40%) in the Nitrate MIBI study (p = 0.001 vs. baseline). Total 21 (60%) out of 35 patients demonstrated viable myocardium. The concordance for viable segments detection between Nitroglycerine MIBI and redistribution TI-201 imaging was found in 100 out of 105 segments (95.24%) for 15 patients, with significant kappa = 0.746 +/- 0.079 SE.

CONCLUSION

The data suggest that use of nitrate augmented 99mTcMIBI protocol in Cardiac SPECT imaging results in improved detection of viable but hypoperfused segments and achieves results similar to those from standard TI-201 rest and redistribution protocol.