Feasibility of one-eighth time gated myocardial perfusion SPECT functional imaging using IQ-SPECT.

PURPOSE: IQ-SPECT, an add-on to general purpose cameras based on multifocal collimation, can reduce myocardial perfusion imaging (MPI) acquisition times to one-fourth that of standard procedures (to 12 s/view). In a phantom study, a reduction of the acquisition time to one-eighth of the standard time (to 6 s/view) was demonstrated as feasible. It remains unclear whether such a reduction could be extended to clinical practice. METHODS: Fifty patients with suspected or diagnosed CAD underwent a 2-day stress-rest (99m)Tc-sestamibi MPI protocol. Two consecutive SPECT acquisitions (6 and 12 s/view) were performed. Electrocardiogram-gated images were reconstructed with and without attenuation correction (AC). Polar maps were generated and visually scored by two blinded observers for image quality and perfusion in 17 segments. Global and regional summed stress score (SSS), summed rest score (SRS) and summed difference score (SDS) were determined. Left ventricular volumes and ejection fraction were calculated based on automated contour detection. RESULTS: Image quality was scored higher with the 12 s/view acquisition, both with and without AC. Summed scores were statistically comparable between the 6 s/view and the 12 s/view acquisition, both globally and in individual coronary territories (e.g. in images with AC, SSS were 6.6 ± 8.3 and 6.2 ± 8.2 with 6 s and 12 s/view, respectively, p = 0.10; SRS were 3.9 ± 5.6 and 3.5 ± 5.3, respectively, p = 0.19; and SDS were 2.8 ± 5.7 and 2.6 ± 5.7, respectively, p = 0.59). Both acquisitions allowed MPI-based diagnosis of CAD in 25 of the 50 patients (with AC). Calculated end-diastolic volume (EDV) and end-systolic volume (ESV) were modestly higher with the 6 s/view acquisition than with the 12 s/view acquisition (EDV +4.8 ml at rest and +3.7 ml after stress, p = 0.003; ESV +4.1 ml at rest and +2.6 ml after stress, p = 0.01), whereas the ejection fraction did not differ (-1.2 % at rest, p = 0.20, and -0.9 % after stress, p = 0.27). CONCLUSION: Image quality and LV functional parameters obtained with a one-eighth acquisition time were statistically comparable to the previously validated one-fourth time protocol using IQ-SPECT. Shorter acquisition times without loss of diagnostic accuracy provide improved patient comfort and streamlined departmental efficiency.

The importance of a correct positioning of the heart using IQ-SPECT system with multifocal collimators in myocardial perfusion imaging: a phantom study.

BACKGROUND: We have recently validated a quarter-time protocol in Myocardial Perfusion Imaging named IQ-SPECT, whose basic principle is to implement a multifocal collimator; However, in clinical practice, it may sometimes be difficult to center the heart in the region of highest magnification of the multifocal collimators (the so-called sweet spot). We therefore aimed to evaluate whether a heart mispositioning may affect results in MPI. METHODS: We simulated a rest study with an anthropomorphic phantom with an in vivo distribution of 400 MBq [(99m)Tc]tetrofosmin, with and without a transmural defect (TD). For each set of images, we performed 5 acquisitions, one with a correct centering and with other 4 degrees of mispositioning. Raw data and reconstructed images were evaluated qualitatively and quantitatively, including no corrections, correction for attenuation, for scatter or for both. We assessed polar plot uniformity, LV wall thickness, and TD and cavity contrast. RESULTS: Images obtained either with a correct heart centering or with mild misposition showed no differences, both qualitatively and quantitatively. Those obtained with major mispositioning differed in uniformity and TD contrast depending on correction parameters. CONCLUSION: This is the first study investigating how a heart mispositioning can affect diagnostic accuracy with IQ-SPECT system. Mild-to-moderate mispositioning (≤2.5 cm) is unlikely to significantly affect results.

IQ SPECT allows a significant reduction in administered dose and acquisition time for myocardial perfusion imaging: evidence from a phantom study.

UNLABELLED: We recently demonstrated in a clinical trial the ability of a new protocol, IQ SPECT, to acquire myocardial perfusion imaging (MPI) studies in a quarter of the time (12 s/view) of the standard protocol, with preserved diagnostic accuracy. We now aim to establish the lower limit of radioactivity that can be administered to patients and the minimum acquisition time in SPECT MPI using an IQ SPECT protocol, while preserving diagnostic accuracy. METHODS: An anthropomorphic cardiac phantom was used to acquire clinical rest scans with a simulated in vivo distribution of (99m)Tc-tetrofosmin at full dose (740 MBq) and at doses equal to 50%, 25%, and 18%. For each dose, 2 sets of images were acquired, with and without a transmural defect (TD). Variable acquisition times were also used for each dose. We analyzed raw data and reconstructed images, including no correction and correction for attenuation (AC), for scatter (SC), or for both (ACSC). Images were evaluated qualitatively and quantitatively in order to assess left ventricle (LV) wall thickness (full width at half maximum of the medial sections), TD, and cavity contrast in the LV wall. Data were compared across different acquisition times within the same dose and across doses with the same acquisition time. RESULTS: Images were visually scored as very-good quality except those acquired with 4 s/view or less at 100% dose and 6 s/view or less with 50%, 25%, or 18% dose, due to false-positive defects. LV wall thickness was not significantly different among all acquisitions. Cavity contrast remained unchanged within the same dose for all images and tended to be higher in AC and ACSC images. TD contrast remained unchanged within the same dose for all images. In SC and no-correction images, contrast was constant for all doses. AC images had significantly higher TD contrast values, and ACSC images showed a drop in TD contrast for a 50% dose. CONCLUSION: IQ SPECT effectively preserved both image quality and quantitative measurements with reduced acquisition time or administered dose in a phantom study. These findings suggest that approximately one eighth of the time, compared with standard protocols with a full dose, or a lower dose at an acquisition time of 12 s/view can be applied in MPI without the loss of diagnostic accuracy.

Deep Inspiration Breath Hold [(18)F]FDG PET-CT on 4-rings scanners in evaluating lung lesions: evidences from a phantom and a clinical study.

OBJECTIVE: To investigate the clinical feasibility of a Deep Inspiration Breath Hold (DIBH) (18)F-FDG PET-CT acquisition in apnea and compare the results obtained between these acts of acquisition in apnea and in Free Breathing in the evaluation of lung lesions. MATERIAL AND METHODS: A pre-clinical phantom study was performed to evaluate the shortest simulated DIBH time according to the minimum detectable lesion that can be detected by our ultrasound scanner. This study was conducted by changing acquisition time and sphere-to-background activity ratio values and by using radioactivity densities similar to those generally found in clinical examinations. In the clinical study, 25 patients with pulmonary lesions underwent a standard whole body (18)F-FDG PET-CT scan in free breathing followed by a 20s single thorax acquisition PET/CT in DIBH acquisition. RESULTS: The phantom study indicated that a 20-s acquisition time provides an accurate evaluation of smallest sphere shaped lesions. In the clinical study, PET-CT scans obtained in DIBH studies showed a significant reduction of misalignment between the PET and CT scan images and an increase of SUVmax compared to free breathing acquisitions. A correlation between the %BH-index and lesion displacement between PET and CT images in FB acquisition was demonstrated, significantly higher for lesions with a displacement>8mm. CONCLUSION: The single 20s acquisition of DIBH PET-CT is a feasible technique for lung lesion detection in the clinical setting. It only requires a minor increase in examination time without special patient training. 20s DIBH scan provided a more precise measurement of SUVmax, especially for lesions in the lower lung lobes which usually show greater displacement between PET and CT scan images in FB acquisition.

Unsuspected Active Sarcoidosis Diagnosed by 18F-FDG PET/CT During the Search for a Primary Tumour in a Patient with Bone Lesions.

Sarcoidosis is a systemic chronic inflammatory disease of unknown aetiology, characterised by granulomatous lesions with heterogeneous clinical manifestations affecting multiple organs and tissues. Although the respiratory system is most commonly affected, the disease may also present with bone lesions. We report the case of a 31-year-old woman who presented with low back pain and no history of cancer and who was found to have suspicious lesions involving the entire spine on magnetic resonance imaging (MRI). The patient underwent 18F-fluorodeoxyglucose (FDG) PET/CT to search for a primary tumour and for staging purposes. 18F-FDG PET/CT revealed a pattern of hypermetabolic activity in widespread skeletal lesions and in a single left cervical lymph node. The primary tumour was not found, thus suggesting a haematologic disorder. Subsequent biopsies of a cervical lymph node and of bone tissue from L4 revealed active sarcoidosis with no evidence of cancer. This underlines the importance of considering all alternatives when hypermetabolic lesions are found on 18F-FDG PET/CT. Furthermore, 18F-FDG PET can be very useful to indicate accessible sites for guiding fine-needle aspiration cytology (FNAC).