Population: This retrospective study analyzed 78 patients (median age: 57 years, range: 32-81 years) who participated in a diagnostic protocol between September 2019 and July 2023. All patients underwent WB-MRI (Diagnostic Line 1, DL1) and one of the two reference diagnostic pathways: FDG-PET/CT (Diagnostic Line 2, DL2) or BS with CT-CAP (Diagnostic Line 3, DL3).

Study Design: The study evaluated four imaging modalities: WB-MRI, FDG-PET/CT, BS and CT-CAP,. The study was divided into three phases:

1. Study of the standard protocols of the proposed imaging modalities DL1, DL2 and DL3 and analysis of scan times.
2. Estimation of energy consumption and emissions of DL1, DL2 and DL3.
3. Collection of radiation dose data for imaging modalities (Dose Length Production – DLP) and recording of contrast agent administration data for CT-CAP and radioactive tracers for BS and FDG-PET/CT examinations.

Phase 1 - Scan Protocol:

1. WB-MRI (DL1): WB-MRI was performed without contrast agents using T1-weighted and T2-weighted sagittal sequences for the spine, as well as axial T1-weighted, T2-weighted, and DWI sequences from the head to mid-thigh. Images were acquired using a 1.5 Tesla scanner (Magnetom Avanto, Siemens) and processed both online and offline. Acquisition time was approximately 30 minutes, with the possibility of repeating suboptimal sequences due to motion artifacts or poor breathing control [table1]
2. FDG-PET/CT (DL2): Patients underwent preliminary evaluations, including blood glucose analysis, before the FDG-PET/CT scan. The scan covered the orbito-meatal line to the mid-femoral diaphysis using a PET/CT DMI DR scanner (General Electric) with a 3D technique. CT was performed using a spiral technique, low dose, and without contrast agents for attenuation correction and anatomical localization. The typical acquisition time was about 15 minutes, with additional scans required in cases of motion artifacts, bladder issues, or taller-than-average patients.[table2]
3. CT-CAP (DL3): This protocol involved multiple phases, including a baseline phase of the upper abdomen, an arterial phase of the upper abdomen, and a portal/venous phase covering the thorax, abdomen, and pelvis. Late-phase imaging could be performed when clinically indicated for liver or kidney conditions. Scans were conducted using two multi-detector CT systems (Somatom go.Top, Siemens).[table3]
4. BS (DL3): Bone scintigraphy included anterior and posterior planar acquisitions performed using an NM-CT8E860 scanner (General Electric). SPECT and low-dose CT scans could be added for areas with suspected radiopharmaceutical uptake.[table4]

Phase 2 - Energy Consumption and GHG Emissions: An analysis of the energy consumption and GHG emission per patient of all radiological equipment for diagnostic activities was carried out. To estimate the energy consumption per patient in active phase (image acquisition phase), of each diagnostic pathway, we estimated the scanner’s energy consumptions from the product of the average nominal power consumption declared by scanners manufacturers and the scan time. After determining the energy consumption of imaging modalities, the total GHG emissions in kgCO2e were calculated using emissions factors specific to the Italian power sector.

Phase 3 - Collection of dose and contrast agent data: Data on radiation doses and the administration of contrast agents or radiopharmaceuticals were retrospectively collected:

• CT-CAP: Included the injection of iodinated contrast agents (Ultravist 370 mg/ml), calculated based on body surface area (BSA).
• FDG-PET/CT: Involved intravenous administration of 18F-FDG (2.5 MBq/Kg) with imaging performed 60 minutes post-injection.
• BS: Required intravenous administration of 99mTc-HDP (8.0 MBq/Kg), adhering to Italian legislative regulations.
• No dose or contrast agent data were collected for WB-MRI, as it does not involve ionizing radiation or contrast agents.

Analysis: Total scan time (T-Total) was converted into hours to facilitate energy consumption and GHG emission calculations. Data were compared across individual imaging modalities and grouped diagnostic lines (DL1, DL2, DL3). Binary comparisons of scan times, energy consumption, and GHG emissions were conducted using T-test. Average dose values for CT-CAP, FDG-PET/CT, and BS, along with average contrast agent administration data, were calculated.