Radiation dose optimization is crucial in pediatric imaging.

Radiation dose optimization is crucial in pediatric imaging.

                                                            K.M Chapagain(RT)

Pediatric radiography is highly dedicated speciality.  For state-of-the-art pediatric radiology highest level of medical expertise and the newest imaging techniques are required for  limiting exposure to ionizing radiation. Child friendly environment is also very important for their proper  co-operation. Specialty education in field of pediatric radiography is essential in order to better understand pediatric diseases and pathologies and to develop advanced imaging techniques tailored to the specific needs of children. 
Plain film radiography ,fluoroscopy ,Computerized tomography ,magnetic resonance imaging and ultrasonography are  the radiological modalities of choice for pediatric imaging.Magnetic resonance imaging and ultrasonography uses non ionic EM radiation and sound wave respectively   for imaging . Plain film radiography and computerized tomography contribute most of pediatric examination and they uses ionizing radiation .Protection from ionizing radiation is more important for rapidly growing pediatric age group because they are in  the most sensitive stage of human life from radiation. So dose optimization is very- very important for imaging of children. Learning of suitable protection method and mechanism for pediatric examination is essential for imaging specialist. Here I am trying to explore some of possible mechanism to reduce radiation dose without significant compromising the image quality.
choices of modalities
We should try to use  modality with non ionizing radiation  whenever possible, for pediatric patient ultrasonography and magnetic resonance imaging are the first line of choice. Pediatric patient are firstly evaluated by such modalities. Doppler ultrasound can be used as vascular imaging modality.
Ultra low dose radiography.
Low dose high quality radiography is essential for pediatric radiography setting.Initially Calcium tungstate screen were used which are latter replaced by rare earth phosphor e.g Gd –oxysulphide which yield greater X-ray absorption and X-ray to light conversion efficiency than CaWo4.Cassette  front with carbon fiber attenuate very minimally and helpful for dose reduction,  but are quite expensive and brittle. Cassette with Du pont Kevlar front are durable and cost effective. Erbium rare elements with atomic number 68 can be used as effective filter to reduce low energy beam.( which only contribute for more entrance skin exposure).Portable and dedicated NICU machine are appropriate for such filter.
  Proper restraining of small and uncooperative child to minimize film retake due to patient motion and  malpositioning is very important. velcro strap are one of example .Radiation beam should be  tightly collimated. and shielding to gonadal region is important for high radiation exam and procedure with repeating exam. Use of  grid and phototiming is discouraged in pediatric radiology setting. Use of  digital radiography with direct image capture device like FPD are the latest modality of choice which have lower radiation dose than computer radiography system.
Ultra low dose fluoroscopy.
Routine fluoroscopy equipment has one of the site where highest radiation dose is exposed. Fluroscopy procedure should be restricted only for those having strong indication otherwise alternative modality should be used. For pediatric suite pulsed fluoroscopy is used to decrease radiation exposure rate. Digital fluoroscopy with low exposure rate is the modern choice for pediatric fluoroscopy.
D. Low dose computed tomaography .
Keeping radiation dose as low as reasonably achievable is important in computer tomography, it remains the most important strategy for decreasing radiation induced potential risk.Dose reduction in  pediatric CT examinations is of particular importance because the risk to children due to radiation exposure is two- to three-times greater than the risk to adults . This is because children’s organs are more sensitive to radiation exposure and they have a much longer life expectancy relative to adults, thereby allowing more time for a potential radiation-induced cancer to develop. To reduce radiation dose in pediatric CT, the most important first step is to carefully assess the risk and benefit of CT for each patient. When alternative imaging modalities with less or no radiation exposure are readily available and that can adequately answer the clinical question, these methods should be considered for use instead of the CT. Multiphase examinations should be avoided if the information obtained from a single-phase scan is already sufficient.When a CT examination is deemed necessary for a pediatric patient, scanning protocols specifically designed for children must be used. 
Adapting the dose level to different patient size is very important in pediatric cases. Patient size-dependent scanning techniques include the use of AEC, manual technique charts and size-dependent bowtie filters. In AEC, the tube current is automatically modulated according to the patient size. The adjustment is based on target noise levels for different patient sizes. For head CT, the mAs reduction from an adult to a newborn of approximately a factor of 2–2.5 is appropriate.
The use of lower tube potentials in pediatric patients to reduce radiation dose has been actively investigated. Pediatric patients are less attenuating than adults, so the lower tube potential settings usually give better iodine contrast without significantly increasing the noise for the same radiation dose. Conversely, we could reduce the radiation dose and achieve the same or improved iodine CNR relative to 120 kV.
Fast rotation time and a high helical pitch are desirable in pediatric CT in order to reduce motion artifacts. Because of tube current limitations, the maximum achievable dose level (determined by maximum mAs/pitch) can also be limited, especially for lower tube potential settings. Therefore, a higher tube potential may still be necessary for bigger children, which demands a weightor size-based kV/mAs technique chart. Third, lower tube potential tends to generate more artifacts than higher tube potential in the presence of high attenuating object such as bright iodine contrast and bone owing to the more significant beam-hardening effect. In addition, lower tube potential may lead to increased noise and deceased contrast of soft tissues and other structures without iodine uptake. Thus, lower tube potential may not be appropriate for every examination and has to be carefully evaluated before its use.

Conclusion-:
To sum up, medical  radiation protection is very important for pediatric imaging. Radiation exposure can be reduced by the help of TDS principle. Imaging expert in the field of pediatric radiology  knows all the principle of dose optimization and limitation in during imaging. Justification for the investigation is also important in such imaging. Dedicated pediatric imaging suite having different dose optimization option and dedicated digital radiography suite specially designed for pediatric imaging  are using widely nowdays.The specialization in pediatric radiography and computed tomography is essential. Due to dose consideration and technological advancement the future  of pediatric imaging will be surely shifted  towards non ionizing modality.
Refrences-
Thomas KE, Owens CM, Britto J, Nadel S, Habibi P, Nicholson R. Efficacy of chest CT in a pediatric ICU: a prospective study.
Kamel IR, Hernandez RJ, Martin JE, Schlesinger AE, Niklason LT, Guire KE. Radiation dose reduction in CT of the pediatric pelvis. Radiology 1994;
Bushberg JT, Seibert JA, Leidholdt EM, Boone JM. Essential physics of medical imaging 2nd ed Philadelphia, Pa: Lippincott, Williams & Wilkins.
American journal of  roentgenology.