With the rise of ultra-high-resolution CT (UHR-CT) and photon-counting CT (PCCT), focal spot size has become an increasingly important specification for manufacturers. While a smaller focal spot can greatly improve detail, each reduction in size multiplies the engineering challenge.

Designing tubes for UHR-CT and PCCT applications isn’t simply a matter of making the focal spot smaller while maintaining other specifications. An ultra-small focal-spot CT tube (typically ≤ 0.5 × 0.6 mm IEC) must concentrate tens to hundreds of kilowatts of electron-beam power into a needle-tip area. That strains electron optics, thermal management, materials, vacuum engineering and precision manufacturing. Before choosing an ultra-small focal spot tube, manufacturers should assess how the tubes address three design challenges: power capacity, stability and tube lifetime.

Reducing focal spot area increases heat flux dramatically. When the linear dimension is reduced to one quarter of that of a standard tube, the same power produces four times the heat density. Because local temperatures can exceed material limits, tube current must be reduced to prevent damage. However, low power increases image noise and hides fine structures. A well-designed tube must balance these competing needs, providing as much power as possible for the chosen focal spot size.

Micrometer-scale shifts in focal position can disturb geometric calibration and degrade images, making stability an important factor in image quality. Smaller focal spots are more susceptible to focal drift (worsened by very high gantry speeds ≥ 250 rpm and high anode rotational speeds) and focal blooming. Practical solutions to preserve focal performance under thermal and rotational stress include advanced flat-plate filaments, dual-end bearing supports, dual quadrupole electromagnetic lenses and mechanically robust tube assemblies.

Tube lifetime is an essential consideration when designing a CT system. When choosing a tube with an ultra-small focal spot, also consider bearing life, anode wear, thermal-fatigue life, vacuum stability and long-term consistency.

Ultra-small focal spot CT tubes are not merely a miniaturization exercise — they require breakthroughs across electron optics, thermal engineering, materials science, vacuum technology and precision manufacturing. Overcoming the conflicting demands of focal size, power, stability and lifetime is essential to unlocking the next generation of CT imaging detail. To learn more about how Dunlee tubes address these challenges, contact [email protected] or visit us at RSNA 2026, booth 3117.