It was experimentally discovered that addition of conductive material to lead insulation resulted in a reduction of radio frequency (RF) induced heating at the lead tip (hot spot) up to 60% [1]. In that experiment the leads were placed in a rectangular phantom so that the tangential electric field along the lead pathway (E_tan(z)) varied significantly. ISO/TS 10974 Tier 3 [2] requires the assessment of power deposited at a hot spot (p). Tier 3 separates analysis of clinically relevant E_tan(z) from calculations of the lead responses to these E_tan(z) using a lead (implant) model expressed as: $$$p = A \times\ |\int_{0}^{L}S(z)\cdot E_{tan}(z)\cdot dz|^2 $$$, where A is the calibration factor, L is lead length, complex S(z) is the transfer function (TF). TF for an insulated lead was published in [3] but electrical properties of the insulator were not provided. If |E_tan(z)| is constant the largest p (p__{WC_uf}) is generated, if phase distribution φ(E_tan(z))=-φ(S(z)) [4]. However clinically relevant E_tan(z) can be non-uniform. Thus p__{WC_uf} cannot be considered as the worst-case power deposition. Our goals in this study were: 1) to perform electromagnetic simulation of insulated leads, the insulation electrical properties of which varied, and to calculate p (EM_p); 2) to numerically obtain the lead models; 3) to calculate the largest p for uniform and non-uniform RF excitations using the lead models.The leads were insulated stainless steel wires of L={40:800:10} mm, ∅1.5 mm with insulation thickness of 0.5 mm. The wire was capped at one end and had a 10 mm long bare segment at the other end. A sensitivity study of insulator electrical properties was performed for a parameter matrix formed by ε_r={2.7,4}, and σ={0.007,0.000024} S/m. S(z) was calculated using the reciprocity approach [5]. The calibration factor was calculated from EM_p obtained for the leads excited from one side by an ideal 64 MHz uniform source. Hot spot integration volume (Fig. 1a) enveloped an area where the power deposition decayed more than 30 dB. For quantitative comparison all results were rescaled to E_tan(z) equal to 1 V/m (peak-to-peak). Non-uniform linearly decayed E_tan(z)=(-2/L)×z+2. p__{WC_lr} was calculated for φ(E_tan(z))=-φ(S(z)).Two highest VLD areas were observed: one near the lead tip and one near the insulator end face (Fig. 1b). They are considered as one hot spot because one continuous area was visible from the temperature rise (T_rise) profile (Fig. 1c). For L=400 mm there is significant discrepancy between the TF previously published [2] and TF calculated in our study (Fig. 2a). Taking into account TF for bare rod [3], it seems that the piece-wise excitation approach used in [2] is not robust at locations close to the lead tip. TF, EM_p (Fig. 3a), and p__{WC_uf} (Fig. 3b) depended significantly on electrical properties of insulation. The lead length, which resulted in the highest EM_p for plane wave excitation, was essentially shorter for ε_r=4. However for σ=0.000024 S/m, p__{WC_uf}(ε_r=4) was smaller than p__{WC_uf}(ε_r=2.7) only for L={360:600} mm and {760:800} mm. For a lead with L>200 mm located symmetrically about the Z axis in the ASTM phantom, p and T_rise are essentially smaller than respective values for plane wave excitation due to: a) E_tan(z) being essentially reduced at the lead ends in comparison with the value at the center, b) S(z) being significantly reduced along the lead pathway. For all L investigated non-uniform excitation resulted in higher power deposition than uniform excitation (Fig. 4a). The ratio p__{WC_lr}/p__{WC_uf} depended on lead length and the insulator conductivity (Fig. 4c). Thus even for electrically short implants, worst case analysis based on results obtained only for uniform E_tan(z) can lead to significant underestimation. Increased insulator conductivity from σ=0.000024 S/m to σ=0.007 S/m resulted in significant reduction of EM_p for L<500 mm, p__{WC_uf} and p__{WC_lr} for all L.Hot spot counting based on VLD or SAR data could result in an improper number of hot spots because thermal heating could merge several separated high-value VLD areas into one thermal hot spot. Electrical properties of lead insulator and clinically relevant E_tan(z) are important initial implant data for RF-induced heating analysis. However, the specific results of this study, e.g., increased insulator conductivity resulted in decreased power deposition, cannot be simply extrapolated to other leads. A further extensive analysis should be conducted to cover different lead constructions.