Case: Pediatric CT of the Chest with the FLASH Mode

Pediatric patients are far more sensitive to radiation and possible radiation induced risks. Although there are no prospective randomized studies providing data of radiation induced cancer in the population the 50 year follow-up of the A-Bomb showed a slight but significant increase in cancer incidence in the population and up to 15 times higher risk for children compared to adults. Therefore minimizing radiation exposure of children is one of the primary goals in our clinical routine. Every single examination of a child requires a risk-benefit calculation for the possible use of any modality. On one hand a possible radiation induced risk for cancer is sometimes balanced by the chance to get the important finding in a child who would be exposed to a greater risk if scanned with a MR scanner under sedation or even general anesthesia, or has a contraindication for MRI, e.g. pacemaker. In these cases CT is mostly the only alternative for a fast and accurate diagnose. If the radiation exposure could be reduced to a minimum, then the benefit for the child would be maximized.

Short scanning time at low dose

With the 2nd generation Dual Source CT scanner, the Somatom FLASH, we have the possibility to scan with a low dose protocol (e.g. 80 kV) combined with a high pitch (i.e. FLASH mode) which utilizes a table speed of approximately 43 cm/s resulting in a scan time of about 0,5 s for a pediatric chest CT. This enables us to perform a CT scan without the need for patient breath hold and minimizes possible motion artifacts.

First pediatric patient on a Flash scanner without sedation and in free breathing

We use the Somatom FLASH in our clinical routine since February 2009 for adults and since April 2009 for children. We scanned the first child in April 2009, which was in fact the World´s 1st pediatric patient to be scanned on a Somatom FLASH without sedation and in free breathing. The result is presented in the following case report.

Case report

A 27 month old boy with known Down Syndrome presented to the Emergency Room of the University Pediatric Hospital with breathing difficulties and fever. A search in our Radiology Information System revealed that this boy presented to the Emergency room 12 months ago with the same complaints and underwent CT scanning of the chest at that time. Since pediatricians didn´t want to sedate the child which could result in a need for continuous mechanic ventilation, the child underwent a chest CT without sedation and in free breathing which resulted in a non-diagnostic scan (Fig. 1). The radiology report stated a non-diagnostic CT scan and recommended a re-scan in sedation if necessary. Two days later the scan was repeated, the child was mildly sedated, but the scan was again non-diagnostic (Fig. 2).
At this time, this was a child who could benefit from a FLASH CT scan, since chest X-ray wasn´t expected to reveal relevant pathology, which was thought to be a broncho-pulmonary malformation and infectious focus. The boy´s father was instructed to stay at the head end of the patient table and simply hold both arms of the child elevated. The scan was performed within 0.5 seconds and resulted in highly diagnostic images, without any evidence of motion or respiratory artifact (Fig. 3). It was clearly visible that the right upper lobe was hypoplastic and the right upper lobe bronchus was early branching from the trachea, several pneumonic foci could be demonstrated throughout the lungs. The radiation exposure was the same as the scan 12 months ago and resulted in a DLP of 48 mGycm.

Conclusion

This case clearly demonstrates that children do benefit from FLASH scanning, since excellent images are obtained with a minimum of radiation exposure (in our case 0.8 mSv) enabling the patient to breath freely and without the need of sedation or general anesthesia. Patient protocols clearly demonstrate that there was no additional radiation exposure in the FLASH scan compared to the initial non-diagnostic scan; from the image quality it is understandable that even a lower dose would have been enough for diagnostic images (tables 1 + 2).
With this case our clinicians start to tend to low dose FLASH CT rather than MRI with sedation or general anesthesia.

Tables 1 + 2: Patient protocols of initial and FLASH scan shows that there was no additional radiation exposure in the FLASH scan even there are 12 months between both scans.

Fig. 1 15 month old boy who underwent chest CT without sedation in free breathing, which resulted in non-diagnostic images.

Fig. 2 Re-scan two days later in mild sedation resulted in mainly non-diagnostic scan.

Fig. 3 FLASH CT scan of the same patient 12 months later at the age of 27 months, in free breathing which highly diagnostic images enabling accurate diagnosis. Related/suggested readings: Mettler et al, J Radiol Prot. 2000;20:353-359
Brenner et al, AJR 2001; 176:289-296
Paterson et al, AJR 2001; 176:297-301
Donelly et al, AJR 2001; 176:303-306
Hall, Pediatr Radiol 2002; 32: 700-706, Neuhauser Lecture