Chronic kidney disease (CKD) continues to cause substantial health burden in terms of mortality and morbidity in India [7], and renal transplantation is the treatment of choice for CKD that offers several advantages [2]. All living renal donors should have a detailed medical evaluation to ensure donor safety, and CT Angiography is the imaging workhorse for their evaluation. CTA shows excellent delineation of renal anatomy, variations and other findings which play a key role in the selection of donors [3]. MDCT can detect accessory arteries, early branching of renal arteries, and renal vein anomalies, with an accuracy of 89–97%, 93–97% and 96–100%, respectively [8].
With the robust use of CTA, the knowledge regarding the risk of radiation and contrast induced nephropathy (CIN) is of prime importance. Though there is no direct evidence to link the radiation received from medical imaging with malignancies, some risk can be associated with even small doses of ionizing radiation. Hence, minimizing dose according to the ALARA principle becomes essential. And with the increased usage of iodinated CM in CTA, the apprehension of the risk of CIN is also increased [9]. The incidence of CIN is dependent on the volume of CM used in CECT examinations as shown by literature [9,10,11]. Therefore, while maintaining the diagnostic image quality, it is also essential to reduce the radiation dose and CM amount during the CTA evaluation of prospective donors.
Dual-energy and turbo flash modes were used in this study to acquire the images. In Third-generation dual-source CT (DSCT) scanners, two tubes operate at different kVp in dual-energy mode. The DECT images have been increasingly used in renal imaging for preoperative workups, evaluation of vascular pathology, and oncological evaluation [12].
Turbo flash mode is a high pitch mode in dual-source scanners, in which ultrafast acquisition of images is possible. In this, both sources operate at the same kVp, and the table accelerates up to 737 mm/s depending on the selected pitch (1.5–3). The gantry rotation time of 0.25 s is the additional factor that helps acquire the images faster in third-generation Dual-source CT.
Image quality analysis
The objective analysis of image quality in this study was based on the attenuation of AA and both renal arteries. The difference in mean attenuation of both renal arteries and AA among the two groups, as well as the differences in CNR and SNR was statistically significant, with higher values in group A. But the subjective analysis showed that there was no statistical significance between two groups, suggesting comparable imaging quality between two groups. Though a comparable CNR, SNR could not be achieved in group B, possibly due to increased noise in TurboFlash mode [13]. MIP, cMPR and VR images demonstrated a fairly good diagnostic assessment and helped in risk stratification of donors (Figs. 3, 4). Also, known drawbacks of high pitch CT scanners like helical artefacts were not seen in any of the cases.
Axial images of contrast enhanced CT renal angiography performed in Turbo Flash mode at renal level in patients with varying body mass index (BMI) show good image quality
VRT images of contrast enhanced CT renal angiography performed in Turbo Flash mode in patients with varying body mass index (BMI) show acceptable image quality
Radiation dose analysis
Third-generation dual-source CT (DSCT) scanners have different tools for radiation dose reduction [14]. An important technique is automated tube current modulation (Care dose 4D in Siemens) which utilizes scout image taken before the actual scan to estimate which region requires greater/lesser radiation doses; and based on the attenuation values acquired, the tube current can be modulated to deliver the appropriate doses to that particular region [15].
Few other methods include reduction in the tube voltage (kVp), tube current (mA), use of different noise filters to process the images during reconstruction, modifying the reconstruction algorithms, and shielding the patient. The ability to create virtual non-enhanced data sets and to minimize image acquisition in the classic triple phase protocol renders DECT a helpful tool in further decreasing the radiation dose [16]. Davarpanah et al. have shown by reducing tube voltage current from 120 to 80 kV there is a significant reduction in radiation that also improved the SNR and CNR [17]. We had also replaced excretory phase acquisition by conventional radiography to further reduce the dose to the patient.
Another important technique is using high pitch, which can be performed by Turbo Flash mode in a third-generation DSCT, which can also perform extremely fast scans.
Because of its improved temporal resolution and faster overall acquisition times, Turbo Flash can decrease cardiac and respiratory motion related artefacts [18, 19]. It can also result in lower radiation dose to patients, according to Sommer et al. [20].
Similar results were obtained in our study, with lower mean CTDIvol, DLP and ERD in Turbo Flash mode, and an overall radiation dose reduction of approx. 32%. These results are in accordance with the previous similar study by Pang et al. [21] where there was a dose reduction of 38%.
Contrast media volume analysis
The incidence of CIN is dependent on the volume of CM, hence the reduction in CM is vital to reduce CIN risk. Adjusting CM volume to the patient’s weight is a simple, robust, and widely used method for individually tailoring CM injection protocols [22].
According to Sodagari et al., 30 ml of iodinated contrast was effective in producing diagnostic quality images in 20 patients with chronic renal insufficiency who underwent high-pitch abdominopelvic (AP) CTA on a third-generation dual-source CT scanner [23]. In our study, with administration of 0.5 ml/kg of contrast media in the high pitch group, there was a reduction in contrast media by 47.5% when compared with conventional protocol using 1 mL/kg.
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